Request for Comments-35: Evolutions to the DownloadSRTMTiles application

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[Request for Comments - 35] Evolutions to the DownloadSRTMTiles application


  • Author: Jordi Inglada
  • Submitted on 22.07.2016
  • Open for comments


What changes will be made and why they would make a better Orfeo ToolBox?

Tiles not found on the USGS server

The DownloadSRTMTiles applicationthrows an exception if a tile is not found. Althoug this is an intended behaviour, I don't think it is appropriate when a long list of tiles is to be downloaded, since a missing tile implies that the download procedure is stopped.

The list of tiles to be downloaded is computed from the envelope of the images given as input. Sometimes, the images cover a fraction of an ocean or other type of area where no tile is available. The application should not fail in these cases.

Several solutions can be proposed:

  1. Have a list of existing tiles in the application. I don't think that the SRTM grid will change in the future, so this option would allow knowing what tiles are expected to be missing in the USGS server. This would also allow to speed up the section of the code which checks every continent to find every tile.
  1. Display a warning using the application log mechanism instead of throwing an exception.
Cached tiles

The application downloads tiles even if they are already present in the output directory. This can be useful to make sure that we have the most recent version, but an option allowing not to download existing tiles would be useful.

List tiles without downloading

The download mode could provide the possibility to list the tiles to be downloaded without effectively performing the download. This can be useful to estimate volumes and downloading times or for many other purposes.

Tile decompression

The downloaded files are zipped, but the OrthoRectification application needs them to be unzipped. An option in the application could allow to unzip the files on the fly. Mickaël also suggested using GDAL capabilities to read inside zip files over the net through vsizip and vsicurl drivers.

When will those changes be available (target release or date)?

Who will be developing the proposed changes?

Anyone willing to do it.


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