Hi Gerd
first see http://www.mkgmap.org.uk/pipermail/mkgmap-dev/2012q1/014145.html
I see two different interpretations: 1) mkgmap encodes the initial heading (A-B) and the final heading (C-D), always using one byte "curve data " for the final heading. 2) display tool displays the initial heading as "direction", and one or two bytes curve data
My theory is that the two byte curve data is used when we have a road where initial heading AND final heading are (very) different from the direction (A-D). Question is: what value is stored in the different fields?
Does anybody already know more details?
Not me :)
If not, what is the best way to find out?
Even though I only ever worked with a map consisting of 3 roads I found it very difficult to keep track of all the data. For the global index I eventually decided that a program that checked theories about how the format worked rather than just displaying the data was very useful. So I would calculate the actual angles and distances for a road segment and compare with the route data. Only print things that don't fit with what is known. Concentrate on one test at a time. I'd be interested in helping out it if possible. A visual program to see large scale layout would probably be useful too, but that is a lot of work. I might try writing as an OSM file or SVG.
I could either try to write a program that displays the data in real maps, or I could simply use try and error in the mkgmap write routine to find out how MapSource reacts one different codings. I played a little bit with the latter and I see differences in the calculated times.
Of course that is all interesting information too. ..Steve