The terrain on self-hosted map differs from that on OpenTopoMap

[AlexBlack772]

Could you please tell me which settings and DEM data sources are used for rendering OpenTopoMap?

I have deployed my own rendering server using SRTM data, but my terrain turns out very smooth and flat. Mountain ridges are much better defined on your map.

I used:

gdalwarp -co BIGTIFF=YES -co TILED=YES -co COMPRESS=LZW -co PREDICTOR=2 -t_srs "+proj=merc +ellps=sphere +R=6378137 +a=6378137 +units=m" -r bilinear -tr 90 90 raw.tif warp-90.tif

gdaldem hillshade -z 2 -co compress=lzw -co predictor=2 -co bigtiff=yes -compute_edges warp-90.tif hillshade-90.tif

[krusty82]

Hi,
Top-O-Map.com and therefore OpenTopoMap does not use SRTM anymore, but Copernicus glo30 data with a resolution of 30m and for Europe Lidar data from Sonny, also with 30m resolution.
The gdal settings are the same, but because the data is muh bigger, the hillshade is computed in chunks.

[AlexBlack772]

Thank you for reply, I’m more interested in Kyrgyzstan—what dataset is used there?

[AlexBlack772]

For example, here is a comparison of three images; the lateral ridges (marked with red arrows) are more clearly visible on OpenTopoMap. I tried using SRTM30 and ALOS30, but the result was still inferior.

[krusty82]

Thank you for reply, I’m more interested in Kyrgyzstan—what dataset is used there?

The entire planet, except Europe is Copernicus GLO-30 Digital Elevation Model https://portal.opentopography.org/raster?opentopoID=OTSDEM.032021.4326.3

[AlexBlack772]

Thank you,

Using Copernicus data with the current settings yields roughly the same terrain appearance; those lateral ridges did not appear.

However, changing

gdalwarp ... -r bilinear -tr 90 90 raw.tif warp-90.tif

to

gdalwarp ... -r bilinear -tr 30 30 raw.tif warp-90.tif

did affect the image - a lateral ridge became slightly visible, but opentopomap looks much better than my map.

So, it seems the difference lies not in the data used (SRTM vs. Copernicus), but in exactly how that data was processed.

[krusty82]

Sorry, I forgot to mention, that when using data with 30m resolution you have to build the hillshade with -tr 30 30 to make full use of the resolution.