For >4 years we have wanted to create Sentinel-1 products for areas around the antimeridian. Specifically Fiji and areas of Chukotka Russia. @jun_lu reported the issue fixed in releases after Oct '20. @marpet suggests subsetting to only one hemisphere. This has not worked for our Sentinel-1 processing.
Using SNAP 8.0.8/S1TBX 8.0.5 results in ~600 GB memory used, >10 hours to produce, and >400 hours of CPU, as the process circumnavigates the globe. gpt.vmoptions Xmx was set to most of our large server’s available memory for these tests. The subset is defined entirely in one hemisphere, 0.1 degrees away from the antimeridian. Processing and results are the ~same for both an External DEM just covering the subset, and Auto-Download DEMs. When using Auto-Download the process reports SRTM downloads of the ~entire circumference of the globe.
The results are in the wrong hemisphere. This image shows a ~geometrically correct, ~correctly terrain flattened, ~correctly subset product, but shifted ~1.2 degrees into the western hemisphere. The antimeridian is the left side of the screenshot below from the western hemisphere, with land polygons superimposed. The subset defined in the processing graph is the eastern hemisphere geocell S17E179 (S16-17, E179-179.9), but the product is located from W179.66 to W178.66 in the screenshot.
I recall implementing other processing across the antimeridian by changing all references to radians. I had also created DEM files at E180 and W181 which are duplicates of W180 and E179 respectively, but with coordinates in the opposite hemisphere. This approach solved some of these issues in other software we developed.
Antimeridian is an odd case, and we maybe one of a very few attempting to use Sentinel-1 to map antimeridian areas. This is definitely not something we want placed at the top of the development/fix list, but should be kept on developer radar.
This graph using 3arcsec SRTM Auto Download uses less memory ~300GB.
1slice_e180.xml (6.6 KB)
S1A_IW_GRDH_1SDV_20170719T173155_20170719T173224_017543_01D56F_DCD0.zip
“POLYGON(( 178.9729607 -15.9729607, 179.90 -15.9729607, 179.90 -17.0272235, 178.9729607 -17.0272235, 178.9729607 -15.9729607))”