[WPS] SRTM topography not properly recognized in geo_em after geogrid – help with .index or workflow?

[aba0327]

Hello,

I'm currently trying to use custom SRTM-based topography data in WPS (v4.x), but encountering issues where terrain height (HGT_M) in the generated geo_em.d0*.nc files appears flat or incorrect.

Process:​

1. I downloaded SRTM data using QGIS and exported it as GeoTIFF (.tif).
2. I used GDAL to convert the .tif to ENVI BIL (.bil) format, applying vertical flipping and converting to Int16:

   • gdal_translate -of ENVI -a_ullr 124.9998611 32.9998611 128.0001389 35.0001389 -a_srs EPSG:4326 -ot Int16 -a_nodata 0 srtm.tif srtm.bil
     gdalinfo srtm.bil

3. I got the following .hdr file (shortened):

   • ENVI
     description = {
     srtm.bil}
     samples = 10801
     lines   = 7201
     bands   = 1
     header offset = 0
     file type = ENVI Standard
     data type = 2
     interleave = bsq
     byte order = 0
     map info = {Geographic Lat/Lon, 1, 1, 124.9998611, 32.9998611, 0.0002777777798352, 0.00027777778086377,WGS-84, rotation=180}
     coordinate system string = {GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137.0,298.257223563]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]]}
     band names = {
     Band 1}
     data ignore value = 0
     default bands = {1}

4. I wrote the following .index file for WPS:

   • type = continuous
     signed = yes
     projection = regular_ll
     dx = 0.0002777777
     dy = 0.0002777777
     known_x = 1.0
     known_y = 1.0
     known_lat = 33.
     known_lon = 125.
     wordsize = 2
     tile_x = 10801
     tile_y = 7201
     tile_z = 1
     tile_bdr = 1
     units="meters MSL"
     description = "SRTM 3-sec Topography height"
     endian = little

5. I added this to GEOGRID.TBL:

   • interp_option = SRTM:four_pt
     rel_path = SRTM:SRTM

6. I successfully ran geogrid.exe, but when I open geo_em.d01.nc, the HGT_M field does not reflect the SRTM terrain correctly — it's either flat, zero, or unchanged from default. Below are two screenshots comparing the terrain field (HGT_M) from the resulting geo_em.d01.nc:
   • Figure 1: geo_em using default topography (working correctly)
     • 
   • Figure 2: geo_em using my SRTM-based topography (not working properly)
     • 

Questions:​

• Is there anything wrong with the .index file above?
• Is any additional processing required for WPS to correctly use SRTM .bil data?
• Do I need to include border pixels (tile_bdr), or preprocess with smoothing or reprojection?

Thank you in advance for any suggestions or clarification. I would really appreciate help verifying whether my .index file is valid, or if I’ve missed any critical steps.

Best regards,
aba0327

 

[kwerner]

Apologies for the delay in response and thank you for your patience. It looks like you had some other posts similar to this and those issues were resolved. Are you still struggling with this issue?

 

[aba0327]

Dear kwerner,

Thank you for your response.
This issue has been resolved.