[mkgmap-dev] [PATCH] Creating contour lines from DEM data

Sat Jul 4 08:59:51 BST 2009

Hi!

I am very much interested in your work as I used srtm2osm, which is no 
longer working, and now I am looking for alternate techniques.

Christian Gawron schrieb:
> Nop schrieb:
>> Sounds interesting. Does it also distinguish minor and major elevation 
>> lines? 
> Currently the types are still hard-coded as follows:
> multiples of 200m: 0x22
> multiples of 50m: 0x21
> 0x20 for all others
 > This should of course be configurable (as well as a "feet" mode).

Should not be too difficult to make this configurable and also turn off 
  the elevation texts for each level. No need to label each 10m-line.

>> What determines the area in which the contour lines are calculated? 
> The bounding box of the tile.

So each map tile must have a bounding box? What happens if there is 
none? Currently I am not generating  them, but that's no problem.

>> Is there a way to avoid an overload with contours e.g. when processing 
>> the whole of Germany inclduing very flat country as well as the the alps?
> You may split the map and use diffeent settings for each tile.

This is still a problem. When creating a map of Germany, I have 440 
tiles, but I cannot tell in advance which of them are too mountaineous 
too show with all altitude lines. Even if nothing crashes, if you show 
10m lines for the whole of the alps, the map size will explode and the 
map consists mostly of altitude lines.

In the past, I have handled it by first creating the contour line .osm 
with srtm2osm and 10m lines. When the size of the output .osm was too 
large, I doubled the base distance to 20m lines and tried again, until 
the output size was within limits. Can you think of a way to integrate 
an upper limit for elevation lines and a try-and-error fitting against 
this limit to your calculations? Or even better, is there a way to 
predict the outcome without doing all calculations first?

bye
	Nop