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PICTURE pocketAPRS

pocketAPRS map making

Some people ask me which program I use to make these maps. This is how it is done (if you are not interested in this click here to go back to the homepage):

I use several home made C-programs which I wrote specifically for this task. First of all I have two programs which can to convert WinAPRS maps to an ASCII format file and back. This ASCII format is the base format I use for the maps. To make PocketAPRS maps I manually extract the vectors from this ASCII file by removing the header and label parts using 'vi', a Unix text editor.

Unix (and Linux) has many tools to manipulate ASCII files. My personal favorit is 'gawk' the GNU implementation of 'nawk'. I still want to learn 'perl' but I never got round to do it as 'gawk', 'sed', 'grep', 'cut' etc. always managed to do the job for me up to now.

Using a gawk-script I now split out the vectors by type (roads, borders, railways etc.). To reduce storage space the vectors need to be concatinated as much as possible. I use 3 small C-programs to group vectors together and a gawk-script to concatinate the vector chains. This must be repeated until nothing can be concatinated anymore, this is done by a shell script. Also a script is used to remove the lattitude and longitude lines that are present in the WinAPRS maps, I don't like them on the PocketAPRS map.

Now that I have the optimized vectors I can concatinate them to get one file with all the vectors. Of course this is another script. Finally I have a C-program that can generate a PocketAPRS .pdb file. Offsets between vectorpoints shall not be too big as these are stored in only 2 bytes. So now it is time to determine the maximum granularity and to manually fix the vector file if needed. Sometimes stray points are left over which can be deleted, sometimes new points have to be inserted half way in a vector. The C-program which creates the map also needs to be changed to contain the map name. Also the colors used in the original map need to be mapped to the PocketAprs types for roads, borders, railways etc have to be determined. Finally I need to program at what zoom level things should show up. Lucky enough the WinAPRS maps all use the same colors so for maps based on those its easy.

Then its time to test the resulting map and if something is not okay fix it (especially at which zoom level features should become visible).

As you see that there are quite a number of steps and its not all obvious. This is the reason why I don't send this tooling into the world for public use - I would get too much mail to support this and I don't want that.

On the homepage you can view screendumps and download the maps produced so far using the described method.


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©Henk de Groot - pe1dnn@nospam.amsat.org (via eMail, remove "nospam.").