I am attempting to automate the processing of Sentinel-1 data using SNAP’s ‘gpt’ on high-performance computing facilities. I’ve run into the main issue that the nodes used to execute the jobs do not have access to the internet, and thus, cannot automatically download the DEM files required for the data processing.
Various previous posts have alluded to this issue but without providing a solution. So this post is to try and work out where the developments are at currently regarding this issue.
My problem would be easily fixed by simply pre-downloading the DEM .zip files to the .snap/auxdata/dem folder, and then letting ‘gpt’ access these local files during the processing. This approach doesn’t work however as the .xml graph parameters expect an ‘externalDEMFile’ rather than an ‘externalDEMFolder’. As indicated in this post, using a folder for an external DEM was on the developers’ to-do list as at Jan. 2017. So Question nr. 1 is: has there been any progress regarding this feature over the last 1.5 year or so?
In addition, this post indicates that even if the DEM tiles are pre-downloaded, ‘gpt’ will apparently still attempt to connect to the tile server to checksum the local files (thereby sending it into an infinite loop of error messages if the connection fails). This would obviously make the solution of pre-downloading DEM data rather useless. So Question nr. 2 is: Can someone confirm that processing the S1 data with pre-downloaded DEM tiles still requires a connection to the server, and can this behaviour be overridden?
I am also facing this issue. I have downloaded STRM 3SEC (which is a folder filled with zip files) and put it in the auxdata/dem folder. GPT still tries to download it from server, which blocks the process when working offline.
Yes, I am pretty sure it is the right folder because when I delete it, it gets automatically created by snap when I relaunch my graph. I indeed have this name format.
Actually, I noticed that I get this error before the attempted download of the strm : “Unable to download http://step.esa.int/auxdata/dem/egm96/ to null”. Could it play a role in not retrieving the dem files?
My dem/egm96 folder is indeed empty. But I got it running on Snap v6.0 with the exact same auxdata/dem folder, and not on Snap v7.0
I added the files manually to .snap/auxdata/, this step was looking for and then it worked.
cp dem/SRTM\ 3Sec/srtm* ~/.snap/auxdata/dem/SRTM\ 3Sec/
cp dem/ww15mgh_b.zip ~/.snap/auxdata/dem/egm96/