The present invention relates to a method and a system for composing a map of a water body. The invention also relates to the use of such a map.

Weather forecast maps as such are known. Shown on these maps are the wind direction and strength for large areas, wherein high and low pressure areas are taken into account. Via whether computers (in Reading, Southern England) the different weather characteristics are determined every six hours at so- called nodes. The Netherlands for instance has about 49 nodes.

Water maps are moreover available for many inland waterways, such as lakes and pools, popular for sailing. Such maps are therefore used for instance to chart the ideal course in the prevailing wind conditions during a sailing race. These nautical maps come in different gradations. The maps may thus indicate which water is navigable, the path of coastlines, what the depth is at different locations, what buoyage is present and what the satellite maps for instance look like. Although water maps already comprise more information than for instance traditional land maps, it is found that such maps are still not always sufficient.

Particularly during regattas it is found that participants who are very familiar with the water on which a race is being held have an advantage over participants less familiar therewith.

It is therefore an object of the present invention to provide in simple and/or efficient manner a more detailed map of a water body. Provided for this purpose according to the invention is a method for composing a map of a water body for the sailing sport, comprising the following steps of:

providing cartographic information of the water body;

determining a generally prevailing wind direction in the area of the water body;

determining wind speeds and wind directions at a plurality of locations in the area of the water body, wherein a dataset is obtained with a wind vector value and the determined generally prevailing wind direction per

location, wherein the wind vector value describes the local wind direction and wind speed;

subdividing the area of the water body into a relatively large number of sub-areas;

selecting wind vector values from the dataset with a predetermined generally prevailing wind direction, and determining from the selection an average wind vector value per sub-area; and

merging the cartographic information and the average wind vector values to form the map with local variations in wind speed and wind direction relative to the predetermined generally prevailing wind direction.

According to the invention it is possible to project wind direction, and preferably wind strength, in more detail on existing maps. Areas with transition from land to water and vice versa are particularly interesting here. The influence of woods, towns, buildings, hills, mountains and so forth on the wind direction and strength on the water is visualized here. Changes in the wind direction, and preferably wind strength, at the transition from land to water thus become visible.

Where convergence occurs and where divergence occurs is for instance visible, as well as how the wind direction and strength vary in detail at average prevailing wind direction and strength for a larger area.

As a result of Coriolis forces and difference in surface roughness of land and water different wind speeds will also occur, with different direction and strength as a consequence, as will be discussed in more detail below.

The dataset, for instance in the form of a database, comprises values representative of the local wind situation, in

particular the local wind direction and/or the local wind speed, in the form of a vector. To each of these values is moreover linked a location, for instance in the form of coordinates, so that the local wind conditions are known at a plurality of locations on or around the water body.

The generally prevailing wind direction, and preferably the generally prevailing wind speed are also linked to these values. The generally prevailing wind can in this latter case therefore also be described in a vector value. This generally prevailing wind direction, and speed, can for instance be derived from a local measurement or can be retrieved from a meteorological service. It may however also be possible to determine the average wind direction and/or speed from the values during a predetermined period. This generally

prevailing wind relates to the generally prevailing wind direction over a larger area, preferably the whole water body, and is used in the selection step to select a plurality of vector values from the dataset.

It is for instance possible for the dataset to comprise vector values determined in the case of different generally

prevailing wind directions. In order to produce a map which shows variations relative to a predetermined, generally prevailing wind direction, vector values are selected which correspond to this predetermined, generally prevailing wind direction or at least correspond thereto. It is also possible, instead of or in addition to selecting on the basis of the generally prevailing wind direction, to select on the basis of the generally prevailing wind speed. The predetermined, generally prevailing wind direction and/or speed can for instance be inputted by the user.

The water body, and preferably the surrounding coastal areas, are subdivided into a number of preferably self-selected sub- areas, and the average local wind direction and/or the average local wind speed is determined in a sub-area. From a plurality of measurements made in a sub-area an average vector value is determined here for the wind speed and the wind direction from the dataset . It is possible here for the average values to be stored separately in the dataset. Each of the average values is preferably associated with a location, wherein the location is representative of the location of the sub-area. The location can for instance designate the centre of the sub- area .

These average values are then merged with the cartographic information so that a map is obtained on which the local wind conditions can be read. It is possible in this way to

visualize where on the water body the wind direction for instance varies from the general wind direction and where for instance local increases in wind speed occur.

Although the variations in the wind directions and the wind speeds relative to the general or average wind direction or wind speed may be small, such variations can be significant for a sailor. A sailor can gain advantage from a locally more favourable direction and/or an increased wind speed. Although the dataset comprises vector values representative of the wind situation which have been determined earlier, these values still give a good indication of how the wind will behave at the time the map is consulted, assuming that the map is relatively up-to-date.

It should be noted that it is also possible to create a dataset having therein only the local wind direction or the local wind speed. In this case only one of these values need be determined. It is however recommended to determine both values, since both the data, in particular local variations therein, are relevant for a water sportsman.

The sub-areas preferably have a size of less than 250,000 m ² , more preferably less than 40,000 m ² , and the sub-areas are still more preferably smaller than 22, 500 m ² . The subdivision of the water body preferably comprises of subdividing the water body using a grid. The sub-areas are substantially rectangular here. The local average wind direction and/or wind speed are preferably determined here every 500 m, preferably every 200 m, more preferably every 150 m and more preferably every 100 m.

According to a further preferred embodiment, it is also possible for the method to comprise a step of determining a size of a sub-area. The size can for instance be entered by a user when retrieving a map. It may also be possible to have the size of the sub-areas depend on the form of the water body. It is moreover possible to vary the sizes of the sub- areas. Use can for instance be made of smaller sub-areas close to land, while larger sub-areas are used in areas further away from land. The variations in the wind close to the coast/shore are in this way represented in greater detail. The cartographic information comprises at least the information for producing a map of the water body. For this purpose the information comprises for instance information on the locations of the shores and possible islands in the water body. The cartographic information preferably comprises the information as it is also available in a water map. It is also possible for the cartographic information to comprise digital maps, for instance with satellite images, which are received from internet. Such online map systems are known.

The map according to the invention is not limited to a determined type of map. The map can thus be composed and consulted digitally, but it is also possible to provide a physical map, for instance of paper and/or plastic. Use is preferably made of a vector as representation of the local wind situation on the map. A map is then provided with a plurality of vectors, each indicating the wind direction and/or the wind speed locally. The density of the number of representations on the map can be made dependent on the scale of the map and the availability of local values.

The invention relates particularly to the production of maps of water bodies accessible to boats, in particular sailboats. The invention relates particularly to maps produced for use in water sports, in particular competitive sailing. The maps are preferably produced so that a user can determine a course on the basis of the local wind directions and/or wind speeds. A water body preferably comprises an inland waterway or a water body in the locality of a coast. An inland waterway must in this context be understood to mean for instance a pool, a river or a lake.

According to a further preferred embodiment, determining the wind direction and the wind speed at the plurality of locations comprises of measuring the local wind direction and the wind speed with a travelling boat, and determining the location of the boat. A plurality of values are in this way provided in efficient manner, each being associated with a location since the location of the measurement of the wind direction and the wind speed is known. The wind direction and the wind speed are preferably measured over the whole surface area of the water body. The measurements are more preferably performed at locations a predetermined distance from each other .

Determining of the location can for instance take place by making use of GPS or a similar system. Measuring of the wind speed can take place by making use of a known anemometer. The wind direction can for instance be measured using an

electronic wind vane.

Measuring of the local wind direction preferably comprises of measuring the local true wind. The true wind can be determined on the basis of correcting the measured wind, the apparent wind, with the course over ground. When determining the true wind, small oscillations of the wind direction and/or wind speed are preferably excluded by filtering. The course can be determined on the basis of multiple determined locations.

Determining of the course preferably comprises of determining the course at a minimal speed. Determining of the true wind from measured wind is known as such.

It can however also be possible to measure the local wind speed and the local wind direction with a stationary measuring station, the location of which is known. Such a measurement can take place both on the water surface, for instance on a buoy, and adjacently thereto, for instance on the shore. Is also possible that determining of the wind direction and the wind speed at the plurality of locations comprises of determining course information of a travelling boat, wherein on the basis of the course information, in particular on the basis of a course of a boat sailing high on the wind, the wind direction and the wind speed are determined locally. The course information can for instance be derived from a

plurality of location determinations of a travelling boat. A course on the wind can for instance be identified by making use of pattern recognition in the course information. A tacking boat can be identified particularly from a zigzag course. Such a course can also be identified on the basis of a known, generally prevailing wind direction. This generally prevailing wind direction can for instance be retrieved from a public database. By assuming that a boat is sailing high on the wind, it is assumed that the local course lies at an angle of ± 45° to the local wind direction.

A further preferred embodiment of the method also comprises of determining oscillations in the wind direction and/or the wind speed, preferably determining oscillations in local wind direction and/or wind speed. The wind direction in particular, and to lesser extent also the wind speed, tend to change periodically. By measuring these oscillations a change in the wind direction and/or wind speed can be predicted. The oscillations are preferably determined on the basis of Fourier analysis. The periodicity of the oscillations can in this way be calculated efficiently. Just as the values of the wind speed and/or the wind direction, the oscillations can be inputted in the dataset, and then for instance averaged for a sub-area. It is however also possible to determine and display the oscillations of the generally prevailing wind. According to a further preferred embodiment of the method according to the invention, determining the wind direction and the wind speed at the plurality of locations comprises of extrapolating a value of a first location to a second

location, wherein the value for the second location is also determined on the basis of geographical information close to the first and second locations. The landscape around a water body, in particular an inland waterway, influences the

behaviour of the wind close to this landscape. Local

variations in wind speed and wind direction occur particularly close to the shores and islands. The geographical information, for instance originating from the cartographic information, preferably comprises information about the relief, i.e. the height of the landscape, in the locality of the water body. If the second location is for instance situated closer to a shore than the first location as seen in a direction into the wind, and it is known that the shore is provided there with relief, for instance in the form of building structures or vegetation, the wind speed will accordingly be adjusted downward. The wind direction close to shores, in particular close to shores with relief, can also vary due to the wind being deflected by the relief.

It is therefore possible according to the invention using fewer local measurements to nevertheless obtain a realistic picture of the local variations in wind conditions by making use of local factors, in particular the relief and the form of the locality. It may moreover be possible to interpolate and/or extrapolate the values of a plurality of locations to a second location, wherein the value at the second location is taken as average of the extrapolations.

The second value is preferably also determined on the basis of the influence of the Coriolis effect. In accordance with the Coriolis effect, wind tends to deflect when it flows from an area of high pressure to an area of low pressure. This deflection is stronger above a water body than above the land surface. Variations therefore occur in the local wind

direction and wind speed at the transition between a land surface and the water body.

A second value can also be determined taking into account the temperature difference between the land, in particular the shore/coast, and the water body. A water body needs more time to cool or heat compared to land surface. If the air

temperature above the land surface is for instance higher, the air pressure there will then be slightly lower than on the water body. A deflection of the wind direction or a change in the wind speed relative to the generally prevailing wind can occur under the influence of this difference in air pressure.

A second value can also be determined taking into account the difference in resistance of the land and the water body. Air generally encounters more resistance above land than above a water body, whereby the wind speed above the water body is greater. At the transition from land to a water body

^refraction' therefore occurs when the air moves at an angle, i.e. an angle differing from parallel or perpendicular, from water to land, and vice versa.

According to a further preferred embodiment, determining the local wind direction and wind speed comprises of determining the location, and preferably the local wind direction and wind speed, in a travelling boat using a mobile unit such as a smart phone, and sending the data to a central unit for the purpose of forming the dataset. The central unit can for instance comprise a computer, for instance in the form of a server. The mobile unit can then send data to the central unit, for instance by making use of wireless communication. The central unit is preferably connected to internet to enable efficient communication between the mobile and central units. The central unit preferably receives data from a plurality of mobile units. Collection of information relating to the local variations in wind conditions can then take place for instance on a plurality of (travelling) boats.

A further preferred embodiment of the method according to the invention also comprises the step of sending the map to the mobile unit. The map with local variations in wind can then for instance be consulted on a boat.

The invention further relates to the use of a map as obtained from the method according to the invention for determining a route of a sailboat over a water body, comprising the steps of:

receiving a starting point and a finishing point of the route; and

determining an optimum route between the starting point a the finishing point on the basis of the local variation i wind direction and/or wind speed.

Such a route can preferably be inputted using a mobile unit as discussed above. The starting point can for instance be determined at the location of the mobile unit. Furthermore, multiple intermediate points can more preferably be set, wherein the central unit preferably calculates the quickest and/or most efficient route between the points on the basis of the map with local variations in wind. The use more preferably also comprises of determining the optimum route on the basis of a polar diagram of a sailboat. The invention also relates to a mobile unit adapted for use of the map. Such a device can for instance comprise a mobile phone. Such a mobile unit can for instance then be used during training for sailing races or for determining the location of a start-line for a sailing race.

The invention also relates to a system for composing a map of a water body for water sports according to the invention, comprising:

a measuring device adapted to determine the local wind speed and the wind direction at a plurality of locations in the water body;

a memory adapted to hold the dataset and to hold

cartographic information of the water body; and

a processing unit adapted to form the dataset from the measurements of the measuring device and to merge the cartographic information and the average wind vector values for the purpose of forming the map.

The processing unit and the memory can for instance form part of a computer, laptop or a mobile phone or other portable computer, optionally adapted as a server connected to internet or another network.

The system preferably comprises a mobile unit such as a smart phone which is provided with or is associated with the

measuring device, wherein the measuring device is also adapted to determine the location. Many of the commercially available mobile phones are provided with a GPS module, whereby such a mobile phone or smart phone can serve as measuring device in the system according to the invention. The measuring device is preferably adapted to make a plurality of location

determinations, more preferably to determine a course of a travelling sailboat as already discussed above. It is possible for the processing device and the memory to also form part of the mobile unit, wherein the mobile unit itself produces a map with local wind variations. According to a further preferred embodiment however, the system also comprises a central unit, wherein the central unit is adapted to receive data from a plurality of mobile units, and wherein the central unit comprises at least the memory for holding the dataset. At least the dataset is stored centrally here and supplemented with data from mobile units.

The invention further relates to a central unit, a measuring device and a mobile unit according to the invention.

The present invention is further illustrated on the basis of the following figures which show a preferred embodiment of the method according to the invention and are not intended to limit the scope of the invention in any way, wherein:

Figure 1 shows a schematic view of a lake;

Figure 2 shows schematically the deriving of the local wind direction from course information;

Figure 3 shows a schematic view of the system according to the invention;

Figure 4 shows a schematic view of the system of figure 3 in more detail;

Figure 5 shows a simplified map according to the invention; Figure 6 shows the stepwise compiling of a database according to the invention;

Figure 7 shows the stepwise production of a map; and

Figure 8 shows schematically the deriving of the true wind direction and speed.

Figure 1 shows a schematic top view of a lake 1. As indicated with numeral 100, the wind comes from the north-west, as also measured by weather stations 4 arranged on shore 3 around lake 1. This figure is oriented with north at the top. The wind direction with speed measured at the position of weather stations 4 is shown in vector form, wherein the direction of the arrow indicates the wind direction and the length the measured wind speed.

As can be seen, the lake is subdivided into sectors. The sectors in this example have a size of 100 metres by 100 metres. Arranged in the sectors are vectors which indicate the average local wind direction and average wind speed in a sector. As shown in figure 1, both the wind speed and the wind direction can vary locally over the surface of lake 1.

In order to chart the variation in the wind direction and the wind speed a sailboat 2 is provided with a measuring station which measures the wind speed as well as wind direction. The sailboat is also provided with a GPS module so that the exact location at the time of the measurements is determined. On the basis of the course over ground the measuring station is adapted to determine the true wind on the basis of the measured apparent wind.

According to this example the boat has already performed five measurements along route 21, these being indicated with the crosses on route 21. Using boat 2 the local wind directions and the local wind speed can be charted by sailing

systematically over lake 1.

From the measurements of a plurality of boats 2 an average wind speed and wind direction are then determined per sector. The measurements as indicated on route 21 are therefore averaged with other measurements taken earlier for the purpose of determining the local wind direction and wind speed. In addition to the direct measurement of the wind speed and the wind direction using for instance a boat 2 or weather stations 4, it is moreover possible according to the invention to derive the wind at a location on the basis of a wind characteristic determined earlier elsewhere, for instance by measurement. A detailed wind map can thus be produced by extrapolation and interpolation. These values for the wind can also be included when determining an average wind per sector.

The locality of lake 1 is taken into account in the

extrapolation, and in particular the relief on shore 3.

Situated upwind of lake 1 are for instance trees 5a, so that it can be determined for a region d that the wind speed there will be lower compared to the location to the south thereof. The same effect will occur downwind of apartment building 6.

Also shown is that the wind direction on lake 1 varies to some extent from the wind direction as for instance measured by weather stations 4. This variation can be attributed to the Coriolis effect, wherein wind is deflected due to the rotation of the Earth. Owing to the reduced resistance above a water surface this effect is greater above lake 1, so that the wind direction above lake 1 is more northerly. Compare for instance the directions of the wind as indicated in region c.

Such an effect also occurs in regions a and b, with the difference that in region a the wind direction at waterside and the wind direction on lake 1 converge, so the wind spee here is higher. In region b the directions are on the other hand divergent, so the wind speed there is lower. The effect of the vegetation 5b on the lee shore can be seen in region e. The wind direction tends here to follow the contours of shore 3.

Is moreover also possible to derive the wind while taking into account the current in the lake. It is also possible to take into account temperature differences between the air above land 3 and water.

In addition to determining the wind direction and wind speed by direct measurement and interpolation and extrapolation, it is moreover possible to determine the local wind direction on the basis of the course of a tacking boat 2 as shown in figure 2.

Boat 2 is provided with a GPS module so that the course of the boat, indicated by 21a and 21b, can be determined. A zigzag structure can clearly be identified in course 21a and 21b and, subject to the wind direction measured with weather station 4, it is possible to determine that boat 2 is tacking. By assuming that boat 2 is sailing as closely as possible to the wind, the local wind direction 100a and 100b can be determined by assuming that courses 21a and 21b are at an angle 22 of 45° to the local wind directions. Figure 2 also shows for instance a change in wind direction around the point indicated by 101.

Figure 3 shows schematically the system 200 for producing a wind chart according to the invention. System 200 is provided with a server 15 connected to the internet which is designated schematically with 14. Server 15 is embodied in this

embodiment as computer and is, as known, provided for instance with a central processing unit, storage means, memory means and input and output means. Server 15 forms and stores a database 16 in which a plurality of data relating to the local wind conditions is stored. In this example the data are stored in a table, wherein each row comprises data associated with a determined location which is defined by coordinates, indicated with the columns 8 for degrees longitude and v for degrees latitude. A wind speed V and a wind direction d are included for each location. Also included per location is an average wind direction dn measured by a fixed weather station 4 at the time of the measurement at the location. It is possible that not every row of all the columns of the table are filled. It is thus possible that only the wind speed or only the wind direction is determined for some rows .

Server 15 is also provided with data 17 from the locality of lake 1. Data 17 are standard water maps supplied by an agency which offers such maps online. Further connected to server 15 is a printer 18 which can print out the produced maps 201.

System 200 is moreover provided with a number of mobile phones 10a and 10b. Mobile phones 10a and 10b communicate via the GSM network and the internet 14 with server 15. Telephones 10a and 10b are provided with a GPS module and transmit their location every 10 seconds to server 15.

In this example telephone 10a is on board boat 2 as shown in figure 2. On the basis of the course information the server can calculate and store in database 16 the local wind

directions 100a and 100b. In this example telephone 10a transmits only location data to server 15, wherein server 15 determines the local wind direction from the location data.

The device 10b, which in this example is on board boat 2 as shown in figure 1, is connected to an anemometer 11. The connection between anemometer 11 and device 10b can for instance be a Bluetooth connection. Anemometer 11 is provided with a velocity meter 12 and a wind direction meter 13. With each transmission of the location data the mobile phone 10b also sends the measured wind speed and wind direction to server 15. These data can therefore be directly inputted into database 16, optionally after addition of the average wind direction dn and conversion of the measured values. It is possible here, on the basis of the measured wind speed, for the true wind to be determined on the basis of a course which can be determined on the basis of the GPS data.

It is also possible to use a more advanced version of an anemometer 11. Such a measuring device is for instance then adapted to determine a compass course, to determine the local water depth, to determine the speed over the water and the air pressure. All these data can then be transmitted to server 15 for further processing.

Also shown is an anemometer 11 which is embodied as a fixed weather station 4 as for instance shown in figure 1. Station 4 can for instance be used to determine the average wind direction dn. It is however also possible, using the

measurements with station 4, to calculate the wind direction and wind speed at other locations using extrapolation taking account of the locality of lake 1. The location of the weather station is then for instance determined in server 15, although it is also possible for weather station 4 to be provided with a GPS module.

As already noted above, server 15 is adapted to receive the measured values from devices 10a, 10b and stations 4, and to calculate the wind direction and the wind speed at locations for which no measurement is for instance available. By means of interpolation and extrapolation and averaging of measurements close to this unknown location an assumption can then be made as to the wind speed and the wind direction at this location. These data are therefore also inputted into database 16.

On the basis of database 16 and map data 17 a wind map can now be composed and optionally printed. At predetermined distances on a map, such as for instance in the middle of a sector as shown in figure 1, vectors can be arranged which are

representative of the wind speed and wind direction. The values from locations falling within a sector are averaged here. It is also possible to merge maps wherein only data from database 16 are used with an average wind direction dn which are roughly similar. It is thus possible to produce different wind maps for wind from different directions.

It is moreover possible for the calculated values to be used in determining the average wind speed and wind direction in a sector. It is also possible to provide two different maps. One map can here comprise data of measured values only, while the other map comprises indications of the wind direction and wind speed calculated by interpolation and extrapolation.

The produced wind maps 201 are sent via the internet 14 to the devices 10a so that they can be retrieved on boats 2. Using devices 10a and 10b and map 201 it is moreover possible to determine a route, for instance along a race route inputted beforehand. On the basis of the data in database 16 and map data 17 the server 15 can then calculate the quickest route. Devices 10a and 10b can then serve as navigation systems on the water and then constantly indicate for instance the ideal course. It is particularly advantageous that devices 10a and 10b, or for instance server 15, take account of the polar diagram of boat 2 when determining the ideal course. Such a diagram can for instance be derived using a device 10b and anemometer 11.

Figure 4 shows the system of figure 3 in more detail. Block 200 is representative here of the raw data received from devices 10 and 11. The data are received here using NMEA 0183 protocol. The raw data 200 comprise, among other information, the wind speed, the wind direction, GPS position, compass direction, water depth, the speed relative to the water, the air pressure and date and time data. These data are processed, indicated with 204, to data 201 which comprise the location, in the form of coordinates, the true wind, the wind speed and a date and time designation. A generally prevailing wind is also determined per unit time. In this example data 201 are stored in the KML format.

On the basis of data 201 the position and orientation of a start-line for a sailing race can for instance be determined, indicated with step 202. It is also possible to analyse the data 201, indicated with step 203. It is for instance possible to analyse a route of a sailed race from these data 201.

In order to compose a map according to the invention from data 201, cartographic data of the locality are downloaded in step 207 from a provider of digital maps 17a. In step 208

cartographic data are merged with data 201. The locality, for instance the lake as shown in figure 1, is subdivided here into sectors of 100 metres by 100 metres. The values of the measured wind speed and wind direction measured in a sector are averaged here. These averaged values are then displayed in a map in the form of vectors which originate at the centres of the sectors. The data of a sailed route, i.e. the positions and the wind speed and wind direction measured at these positions, are also displayed on the map. In step 206 such a map is outputted, for instance by providing the map digitally via internet or printing the map with a printer 18.

Is also possible for the size of the sectors to be input into a device 10 or 11 in step 208. The user can input the degree of detail of the local wind direction and wind speed. On the basis of the entered size of the sectors, the information is then merged in step 208 and sent to devices 10,11.

In a step 205 a polar diagram is produced from data 201 on the basis of the measured speeds and the courses sailed by a boat. These data can also be outputted.

Figure 5 shows a simplified map according to the invention. It can be seen that the area is subdivided into sectors, wherein the average wind speed and wind direction are indicated using a vector in each sector where measured values are available, i.e. the sectors where sailing has taken place.

Figure 6 shows the stepwise filling of a database which can be used to produce a map according to the invention. When a start is made with collecting data, the user defines a number of labels which can be used to identify the collected data. Use is made in this example of the following seven labels:

Labels :

1 Country

2 Year

3 Regatta

4 Race

5 Boat type

6 Activity type (Racing, Touring, Training, )

7 Notes (free text) These labels enable easy retrieval of the data from the database, for instance on the basis of a single race of a regatta. It is of course also possible to change the labels or add new labels. After input and optional amendment to or addition of the labels, the collection of data can begin.

In this example a sailboat is used which is provided with measuring instruments for measuring a plurality of parameters. These measuring instruments are connected with a suitable interface to a central unit which is moreover able, on the basis of the measured parameters, to determine a further number of other parameters. The measured and determined parameters are summarized in table 1:

Table 1

14 Longitude Longitude GLL 438.717

E or W (East or E or W (East or

15 West) West) GLL E

16 Depth Depth, meters DBT

Depth unit

17 Depth Units meters DBT

Knots (speed of

vessel relative

18 water Speed to the water) VHW

19 Water Speed Units Units N = Knots VHW

20 Temperature Degrees MTW

Unit of

Measurement,

21 Temperature Unit Celcius MTW

New data are generated once per second which are moreover associated with the defined labels and a unique boat

identification number. It is possible here for the collected data to be stored locally in a so-called log file, although it is also possible for the collected data to be stored directly in a central database DB.

Prior to storage of the collected data in the database, four further parameters are calculated from the collected data as included in table 2 below.

Table 2

Although as stated some commercially available instruments for use in sailboats are able to derive for instance the true wind direction and speed, it is recommended to derive these parameters as shown schematically in figure 8. The True Wind Direction (TWD) and True Wind Speed can then be calculated on the basis of the following formulae:

T = -JS' + A ² -{2xSxAx. coste)}

A ² - T ² -S ²

fi=

2 x T x S

Θ - arccos(?J

TWD = H ±9 wherein :

H = boat heading

T = True Wind Speed

TWD = True Wind Direction

S = Boat speed

Ά = Apparent wind speed

! = Apparent wind angle

2 = True wind angle

As discussed above, it is also possible for the measuring instruments on the sailboat to first store the data in an offline log file which can subsequently be imported into the database. Determining the true wind direction and speed then takes place during import.

For each track or dataset, which for instance corresponds to a single race or journey, an average true wind speed and direction are moreover determined which are associated with each measurement of this track. This average true wind direction and speed are then indicative of the generally prevailing wind speed and direction. When the data are stored directly into the database, the average true wind speed and direction can be determined later, for instance when no further data are received from the boat. When a log file is imported, the average true wind speed and direction can be determined during import.

Once collection of the data has ended, the database comprises for each measurement the data as stated in tables 1 and 2, a unique boat identification number, the labels and the average true wind direction and speed.

Producing a map from the data of the database is shown

stepwise in figure 7 . In a first step a number of selection criteria are entered here by the user. The selection criteria are used to retrieve measurements from the database. These selection criteria can for instance comprise the above stated labels. It is for instance possible to opt to display only the data from a specific race of a regatta.

It is however also possible to select measurements from the database on the basis of the location, for instance on the basis of the GPS coordinates, and a generally prevailing wind direction and/or speed. Measurements from for instance different races and even from different days can in this case be merged to produce a map. If the forecast is known on a day for prevailing wind direction and strength for the whole area, is then possible to select these measurements which are most suitable for the average wind direction and speed in the sub- areas to be selected. The results hereof can then be projected onto a nautical chart to be selected.

On the basis of the selection criteria the first step the data which meet the selection criteria selected from the database in step 2.

The user can then set the size of the sectors in the grid. It is optionally also possible to specify whether the path or track covered, the wind indicators on the track and/or the grid itself must be visible on the map. It is also possible for the system to automatically define a grid, for instance on the basis of minima and maxima in the GPS coordinates of the data selected from the database.

An average true wind direction and an average true wind speed are then calculated for each sector on the basis of the measurement data in the database falling within the range of this sector. The average true wind speed and direction determined per sector are moreover written to the database. This makes reproduction of the same map more efficient.

In a final step the average wind speed and direction per sector are then displayed on a map in vector form, and the thus produced map is thus written to a file and/or displayed.

A map is thus created which visualizes the local wind speed and wind direction relative to a generally prevailing wind. This knowledge is extremely important, for instance for' sailing races. Local sailors often know which coastlines are or are not favourable to approach in a prevailing wind. A small structural rotation of the wind of several degrees can already make the difference here between winning and losing.

The present invention is not limited to the shown embodiments but extends to other embodiments falling within the scope of the appended claims.