[mkgmap-dev] Process for Creating Contour Maps?

Mon Feb 22 07:10:02 GMT 2010

Jeffrey Ollie schrieb:
> Does someone have wiki pages describing the best procedure to create
> contour maps for Garmins?  It seems like a number of people are having
> some success but it doesn't seem to be very well documented.  I'm
> working though trying to get groundtruth to generate .osm files with
> contours in them and then using mkgmap to create an .img file but
> mkgmap is segfaulting.   In any case though, I'd like to get contour
> maps using better data than the STRM that groundtruth uses. My
> ultimate goal is to generate contour maps for a trip out to the Grand
> Canyon this summer.
Dear Jeffrey,

there are two different approaches:
- Using srtm2osm to generate contour lines as osm files.
- Using mkgmap to generate the contour lines directly.

In both cases you'll need appropriate entries in your style file to 
determine which contour lines are mapped to major/medium/minor contours 
(0x22, 0x21, 0x20).
I use
# Contours take their name from the elevation setting.
contour=elevation & ele ~ '\d*[02468]00'
    { name '${ele|conv:m=>ft}'; }
    [0x22 resolution 18]
contour=elevation & ele ~ '\d+[05]0'
    { name '${ele|conv:m=>ft}'; }
    [0x21 resolution 21]
contour=elevation
    { name '${ele|conv:m=>ft}'; }
    [0x20 resolution 23]
for this purpose.

Currently, the internal generation of contour lines can only cope with 
maps fitting into a single data tile. It can read SRTM geotiffs, ASTER 
geotiffs and HGT files. I use the following options:
--contours
--dem-type=ASTER
--dem-increment=20
--dem-maxlevels=200
--dem-path=ASTER


Hope that helps
Christian