How to use multiple data sources(srtm_3s+default) to perform geogrid on topography data?

L

lyg

New member
Hello, WRF Forum!
The problem I encountered is the same as the post ( SRTM_3S), but this problem seems not to have been resolved. Therefore, to facilitate my direct adoption of his statement, I proceeded accordingly.
I have successfully imported the srtm 3s data as static topography data and used it in my setup.
Since the srtm 3s data does not cover the entire model area, when I used namelist.wps and set "geog_data_res = 'srtm_3s+default'", the following occurred:
The output of HGT_M was displayed as 0 in all other places in the model area where the srtm_3s data did not exist. I originally thought that in the case of a single or multiple sources in the geographic grid not covering the entire area, it would fill the remaining area with the "default" source. However, it seems that the geogrid checks whether the specified source has any data in the model area and then only uses that source.

Please refer to the following attached figure:


My WPS version is 4.6.0.

The relevant entries for srtm_3s in my "GEOGRID.TBL" file:
interp_option = srtm_3s:average_gcell(4.0)+four_pt+average_4pt rel_path = srtm_3s:srtm_3s/
rel_path = topo_srtm_3s:topo_srtm_3s/

Please refer to the following namelist.wps:
&share
wrf_core = 'ARW'
max_dom = 3
start_date = '2025-07-26_00:00:00', '2025-07-26_00:00:00', '2025-07-26_00:00:00'
end_date = '2025-07-27_00:00:00', '2025-07-27_00:00:00', '2025-07-27_00:00:00'
interval_seconds = 3600
io_form_geogrid = 2
debug_level = 0
/

&geogrid
parent_id = 1, 1, 2
parent_grid_ratio = 1, 3, 3
i_parent_start = 1, 330, 260
j_parent_start = 1, 125, 520
e_we = 901, 922, 922
e_sn = 601, 982, 982
geog_data_res = 'srtm_3s+default', srtm_3s+default', srtm_3s+default'
dx = 9000
dy = 9000
map_proj = 'lambert'
ref_lat = 35
ref_lon = 115
truelat1 = 30
truelat2 = 60
pole_lat = 90
pole_lon = 0
stand_lon = 115
geog_data_path = '/public/home/gly/wrf/GEOG/WPS_GEOG'
opt_geogrid_tbl_path = './geogrid/'
/

&ungrib
out_format = 'WPS'
prefix = 'PRE'
/

&metgrid
fg_name = 'PRE', 'SUF'
io_form_metgrid = 2
opt_metgrid_tbl_path = './metgrid'
/
 
Hi, Many apologies for the delay in response to your question. Have you managed to solve the problem yet, or are you still experiencing the issue?
 
Hi, thank you for following up. Unfortunately, the problem has not been solved yet, and for the time being I have given up on using high-resolution terrain data.

The core of the issue is that I tried to fill the nested domains d02 and d03 with high-resolution topography, but the terrain height is only correct where the high-resolution data is available. In areas where I do not have high-resolution data, I expected geogrid to fall back to the default terrain data and fill those regions automatically — but it doesn't seem to do that.

Could you help clarify whether this behavior can be fixed, or whether it is simply a fixed limitation that only one set of terrain height data can be used? I've attached a reference image below.

domain.png
Thank you for your help.
 
Hello !
I came across your post ,,,, the SRTM_3S data coverage and the "zero-filling" issue in geogrid. I think I might have identified why the fallback to "default" data isn't working as expected in your setup.

In your GEOGRID.TBL, check the HGT_M section for the following line:
fill_missing = 0.

If this line is present, geogrid will treat any missing high-resolution tile as a fixed elevation of 0 meters instead of looking for the next available source in your geog_data_res list. Try to :

1)Comment out or remove fill_missing = 0. from the HGT_M section in your GEOGRID.TBL.

2=Ensure your index file (inside your srtm_3s data folder) correctly defines a missing_value (e.g., -32768.) that is not 0.
This should force geogrid to properly trigger the fallback to the default GMTED2010/GTOPO data where SRTM tiles are missing.

Hope this helps you get those nested domains working!
 
Thank you for your thoughts and reply. However, your speculation seems to be incorrect, because I have tested this before. To avoid any misjudgment due to memory confusion, I re‑ran the tests, and the results are consistent with my memory: this treatment leads to extremely abnormal terrain height values.

Below are the results with fill_missing = 0. and geog_data_res = 'default':
Min/Max: 0.00 / 6312.71
Click to expand...
The maximum terrain height in d01 seems problematic, considering that the highest point of the Tibetan Plateau is around 8000 m.
domain.png

Below are the results with fill_missing = 0. and geog_data_res = 'srtm+default':

Min/Max: 0.00 / 6314.73
Click to expand...
The maximum terrain height still appears problematic.
domain.png

Below are the results with # fill_missing = 0. and geog_data_res = 'srtm_code+default' (note: missing_value = -32768 was already set in the index file; fill_missing = 0. was commented out):
Plotting fails.
Min/Max: 0.00 / 108547517437488136192.00
Click to expand...
The maximum terrain height is extremely abnormal.
Code error:
shapely.errors.GEOSException: TopologyException: side location conflict at 134.92306518554688 33.535152435302734. This can occur if the input geometry is invalid.

One more issue worth noting:
When fill_missing = 0. and geog_data_res = 'srtm_code+default' are set in namelist.wps, and the default file for LANDUSEF (the 1 default) is replaced with new land use data, a series of similar errors appear during geogrid. One of them is:
point (10001, 11131) has an invalid category of 0.
 
@lyg
Can you attach your modified GEOGRID.TBL and your index file for the SRTM data so I can take a look? Thanks!
 
Thank you for your reply! As you requested, below are my modified GEOGRID.TBL and the index file for the SRTM data. Please note that I have since downloaded a larger‑area SRTM dataset, so the current data extent is somewhat larger than the domain shown in my previous plots. I would greatly appreciate any further guidance you can offer. Thank you!
 

Attachments

Thanks for sharing those. There are a few things I noticed that may be causing issues.

1. The namelist.wps printout your provided in your initial message, uses the following setting:

Code: 
geog_data_res = 'srtm_3s+default', srtm_3s+default', srtm_3s+default'

However, in the GEOGRID.TBL, you use the path "srtm," without the "_3s." Whatever name is used in the GEOGRID.TBL is the one you need to specify in the namelist. Can you verify that you are actually using geog_data_res = 'srtm+default' and not 'srtm_3s+default?'

2. In the namelist, the settings for geog_data_res are missing quotes (') for d02 and d03. Each entry should have an opening and closing quote mark, so that it reads:

Code: 
geog_data_res = 'srtm+default', 'srtm+default', 'srtm+default'

3. Please make the following modifications to your GEOGRID.TBL. Instead of simply adding a couple of lines for SRTM under the existing HGT_M section, add a separate section for SRTM and then remove those lines from the existing section. So it should look like this:

Code: 
===============================
name = HGT_M
        priority = 2
        dest_type = continuous
        smooth_option = smth-desmth_special; smooth_passes=1
        fill_missing=0.
        interp_option =       srtm:average_gcell(4.0)+four_pt+average_4pt
        rel_path =       srtm:srtm/
===============================
name = HGT_M
        priority = 1
        dest_type = continuous
        smooth_option = smth-desmth_special; smooth_passes=1
        fill_missing=0.
        interp_option = gmted2010_30s:average_gcell(4.0)+four_pt+average_4pt
        interp_option =     gtopo_30s:average_gcell(4.0)+four_pt+average_4pt
        interp_option =      gtopo_2m:four_pt
        interp_option =      gtopo_5m:four_pt
        interp_option =     gtopo_10m:four_pt
        interp_option =        lowres:average_gcell(4.0)+four_pt
        interp_option =       default:average_gcell(4.0)+four_pt+average_4pt
        rel_path = gmted2010_30s:topo_gmted2010_30s/
        rel_path =     gtopo_30s:topo_30s/
        rel_path =      gtopo_2m:topo_2m/
        rel_path =      gtopo_5m:topo_5m/
        rel_path =     gtopo_10m:topo_10m/
        rel_path =        lowres:topo_gmted2010_5m/
        rel_path =       default:topo_gmted2010_30s/

After making these modifications, please run it again and let me know if that makes any difference. If you are still experiencing the issue, I'd like to try to repeat the problem. I do have SRTM data available, but it covers a much larger area. If possible, can you share your SRTM files with me so I can use exactly what you have? I'm sure the files are too large to attach here, so see the forum's home page for instructions on sharing large data files.
 
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