[gdal-dev] How to add labels to DEM contour lines

[Open Land LLC]

Hi everyone, this is my first post. I've also posted this to
https://stackoverflow.com/questions/78751101/labelling-contour-lines-with-ogr-style

I'm trying to add labels to DEM contour lines.

I'm working with GDAL 3.6.2. , which I installed using Anaconda . I have
some DEM data from USGS which I wrote as a contour map to a KML file using:

    gdal_contour small.tif /home/ubuntu/node/geotools/contour.kml -i 3.0 -f
KML -a ELEVATION

When I open contour.kml in vim, I can see that its made up of features like:

<Placemark>
<Style><LineStyle><color>ff0000ff</color></LineStyle><PolyStyle><fill>0</fill></PolyStyle></Style>
<ExtendedData><SchemaData schemaUrl="#contour">
<SimpleData name="ID">39</SimpleData>
<SimpleData name="ELEVATION">525</SimpleData>
</SchemaData></ExtendedData>
<LineString><coordinates>-89.2626638689733,46.1525006611575
-89.262663868958,46.1525469572921 -89.2627325352002,46.152622208059
-89.2628251277396,46.1526266807347 -89.2629177202847,46.1526141000471
-89.2629982621728,46.1525469573863
-89.2629982621882,46.1525006612516</coordinates></LineString>
</Placemark>

Clearly there is a style component available , but I'm not sure how to work
with it to add elevation labels or custom colours. My suspicion is that
OGR_STYLE is used to do things like this (
https://github.com/OSGeo/gdal/issues/835)(https://gdal.org/user/ogr_sql_dialect.html#ogr-style
), but I can't find any examples. How can this be done?

Thank you very much,

KC
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