[mkgmap-dev] [PATCH v4] contours

Thu Jul 9 20:10:52 BST 2009

Nop schrieb:
> But now the real problem starts: How do I use the contour functions?
>
> You say: "- Now the OSM styling engine is used to set labels, types & 
> resolution of the contour lines. "
>
> How does this work? What rules are required? How can I distinguish 
> between minor and major lines, I did find some code that adds some 
> tags and then does some conversion, but there is nothing there for 
> minor/medium/major contour lines.
The code just sets "contour=elevation" and "ele=<level in meter>", so 
you can do the rest with the style, e.g. like this:

# Contours take their name from the elevation setting.
contour=elevation & ele ~ '\d*[02468]00'
        { name '${ele|conv:m=>ft}'; }
        [0x22 resolution 18]
contour=elevation & ele ~ '\d+00'
        { name '${ele|conv:m=>ft}'; }
        [0x21 resolution 20]
contour=elevation
        { name '${ele|conv:m=>ft}'; }
        [0x20 resolution 22]

> How would I apply styles with --dem-maxlevels? When the levels 
> increase, so must the major contour distances, otherwise more and more 
> lines will be major while minor lines disappear from the map.
Ok, that's a valid point - I have no answer yet.

> I also do not want all minor contour lines to be tagged with an 
> elevation, that clutters up the map. But I see no way to suppress this.
I think there is a special character (like the one for the highway 
symbols) which "hides" the label unless you point on the line. I will 
have a look.
Actually, with the styles above I have no problem with the labels 
cluttering the display.
> And eventually, how do I get the proper input data from CGIAR and 
> ASTER? What does a proper input file look like that the contours 
> function can process? I am only familiar with .hgt.
The CGIAR files are GeoTIFF files which cover 5x5 degrees. You can get 
them from http://srtm.csi.cgiar.org/. The ASTER data 
(http://asterweb.jpl.nasa.gov/gdem.asp) also comes as GeoTIFF files 
(each covering 1x1 degrees as the SRTM HGT files).

Best wishes
Christian