Map overlays

Map overlays are images that are visible in the Browse map screen on your navigation device at a certain zoom level.  An example of this is the preinstalled satellite imagery that is visible when zoomed out.

You can create your own custom map overlays for areas such as large exhibition halls, amusement parks, walking routes, or coastal maps.

For example, CeBIT is one of the world’s largest trade shows and it can therefore be quite a challenge to find your way around.  Wouldn’t it be useful to add a map overlay of the CeBIT exhibition grounds to your navigation device?

Here is a map of CeBIT:

mapoverlay

 

And here is the same area shown on a TomTom navigation device:

mapoverlay2

 

Let’s see how these maps could be combined.

Creating a map overlay

A map overlay consists of an image file with an accompanying .SAT file containing some basic information.  You will need to know the GPS coordinates of the top left corner and bottom right corner of your image file (in degrees) and the size of your image (in pixels).

1.Save your image as a .JPG, .BMP or .GIF file (for example, cebit2.gif).  The maximum size of the image is 2040 x 2040 pixels.

Note: You cannot name your file with the same prefix as any existing pre-installed map overlays eg. eux, eur or usa. To see which prefixes are already in use, look in the .ver files in the raster folder on your device.

2.Create the .SAT file.  Open a text editor such as Notepad (Windows) or TextEdit (Mac). You will need to enter 9 lines of text. 
 
Line 1 - filename of the image file.
Line 2 - GPS coordinate of the top left corner of the image (longitude).
Line 3 - GPS coordinate of the top left corner of the image (latitude).
Line 4 - GPS coordinate of the bottom right corner of the image (longitude).
Line 5 - GPS coordinate of the bottom right corner of the image (latitude).
Line 6 - Minimum zoom level for image to be visible (min = 0).
Line 7 - Maximum zoom level for image to be visible (max = 65,535).
Line 8 - Width of image file in pixels.
Line 9 - Height of image file in pixels.
3. Using our example, these 9 lines would be:

cebit2.gif

9.79775

52.33136

9.81312

52.31763

0        

30

304                

440

               

Tip: It is best to limit the zoom range to a range within which the overlay is useful.  In this example the zoom range 0-30 has been selected, as the image is quite small.  This will make the image visible for approximately the bottom third of the zoom bar.  When using a large image, for example satellite imagery of several countries, a zoom range of 2000–65535 might work well and will make the image visible for approximately the top third of the zoom bar.

4.Save the file with the same filename as your image file and with the extension .SAT (for example, cebit2.sat).

Note: You cannot name your file with the same prefix as any existing pre-installed map overlays eg. eux, eur or usa. To see which prefixes are already in use, look in the .ver files in the raster folder on your device.

5.Copy both files (in our example, cebit2.gif and cebit2.sat) to the raster folder on your device.
6.Go to the Browse map screen on your device, tap Options and make sure that the Images box is selected. 

That’s it!  In our example, the end result would be a map of CeBIT visible on your TomTom device:

mapoverlay3