Contents - Index


Country & State boundary data

Why would I want this data?

Adding the Country & State boundary data allows boundaries to be drawn on the generated ground path image and, more importantly, allows the creation of overlay bitmaps which you can subsequently use to add grid lines and country boundaries to satellite images, allowing much easier interpretation when cloud is present.

Where do I obtain this data?

Because this data is static, and quite large, it is not included in the main download archive.  You can download a 426KB zip file containing the data from www.satsignal.eu --> Satellite Tools, WXtrack, Downloads.  After downloading, extract the file Countries.dat from the Zip archive to the folder containing WXtrack.exe.  You should not need to download the data more than once.

How does WXtrack use this data?

WXtrack uses this data in two ways, to create country boundaries on a background picture (in certain modes) if you request this, and indirectly in the generation of overlays.  You can control how overlay maps are presented by downloading a program Make Overlay from www.satsignal.eu --> Mapping Tools which will allow you to make a master overlay background 30MB file called Overlay.bmp in the executable folder.  You can edit this image if you wish, but note that the palette indices must be preserved for subsequent use with SatSignal.  If you don't wish to generate the data, fortunately it compresses down into about 0.5MB and can be downloaded from the WXtrack Web page --> Satellite Tools, WXtrack, Downloads.

If the Save Pass Details option is checked, each time a ground map is generated a new overlay bitmap named according the standard file naming conventions will be generated and saved in the executable folder.  Each overlay bitmap will occupy some 2MB of disk space.  It is your responsibility to clear out these files occasionally.

My PC says it doesn't have enough memory to generate Overlay.bmp

Generating the large bitmap requires more memory than using the bitmap, as all of the bitmap needs to be in memory at once.  On PCs with very limited memory (less than the 32MB recommended for WXtrack) the generation process may therefore take many minutes.  Alternatively, you can download the ready-built bitmap from the Web, where the 31MB bitmap has compressed nicely into a 404KB zip file.  You can download the zip file from my Web site at: www.satsignal.eu --> Satellite Tools, WXtrack, Downloads.  

Why did you use a large bitmap saved on disk?

It would have been possible to generate the overlay bitmap every time the program is run - it would only add a few seconds to the launch time - at least on those PCs with adequate memory.  However, holding the bitmap in memory would take up 30MB of memory allocation, which could impact either WXtrack or other programs in use at the same time.  By using a disk bitmap, together with Windows system functions that allow a file to be mapped into memory, the very minimum physical memory is used by the overlay bitmap, and all the access is handled directly by the operating system so it is fast and efficient.  Using a run-length coded format would have been more efficient on storage,  but is not supported for writing by Delphi and would require more CPU at run time.

The file attributes are set to read-only to make deleting the file a little more difficult, but the program will run quite happily without the file.  It will automatically try and recreate the file if it does not exist.

How is the overlay data saved?

The overlay data is saved in a standard Windows bitmap (.BMP) file allowing its use in either an image processing program or with SatSignal.  The overlay image must in 256-colour format.  The palette in the overlay image is assumed to be a standard Windows palette and the following palette index values are used:

  0 - black (timing marker)
  2 - dark green (land)
  4 - dark blue (sea)
12 - mid grey (timing marker)
19 - white (timing marker)
13 - red (grid lines)
15 - yellow (country or state border)
18 - cyan (graphic overlay)

Disclaimer

I obtained this data a little while ago.  It is intended purely to aid the interpretation of satellite images, and there is no intention to make any political statement or cause offence by any information contained in this data.  I do not vouch for its accuracy.  Please accept this data in the spirit which it is offered.