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I want to be able to download high resolution 3 arc degree resolution (90 meters) from NASA's earthexplorer.gov site. However it is a bit confusing for a beginner like myself. I want to be able to do this for my country i.e. India. I go here http://earthexplorer.usgs.gov/ and by pressing shift I zoom into the area of interest by creating a rectangle. Then it displays 4 coordinates and then I ask for datasets. I get so many options and each are of very small sizes. Am I supposed to download all of it or just any one of it ? If I am supposed to download all of it is there a way to do it all in one download ? I presume then I will have to use progamming code to concatenate these separate .hgt files together.

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You will find explanation on the SRTM datasets here:

https://lta.cr.usgs.gov/SRTM2

The download site offers ASTER DEM, GTOPO, and SRTM with and without corrections. I assume you want the last one.

The 3 arc dataset cover 1 degree x 1 degree areas. depending on the size of your bounding box, that can be one or several files.

Once downloaded, you can stitch them all (they align, but don't overlap), or build a vritual raster with gdalbuildvrt to avoid large files.

  • Technically, they do overlap, by exactly one pixel. This is by design. Furthermore, the overlapping pixel is guaranteed to have the same value (to aid in stitching them together). – Vince Sep 13 '14 at 11:43
  • Thanks for your prompt response Andre. If I want to do a bulk download for my country (i.e. gather all the tiles) is this the best link to grab it from dds.cr.usgs.gov/srtm/version2_1/SRTM3 i.e go under Eurasia and grab the relevant lat/lon files ? – gansub Sep 13 '14 at 11:56
  • I would favour that method. I'm not sure about other download locations. I downloaded the SRTM3 files of my interest a long time ago with maperitive, and saved them for further use with other software. See also gis.stackexchange.com/questions/4873/downloading-srtm-data about bulk downloading, and the other links on the column "Related" to the right. – AndreJ Sep 13 '14 at 13:02
  • I saw that link and I used wget to do a bulk download. – gansub Sep 13 '14 at 13:49
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I recently wrote an SRTM download tool that works from the free and open-source GIS, Whitebox Geospatial Analysis Tools (which can be downloaded here). The user simply specifies the range of lat/long values for their area of interest and the tool will download all of the .hgt tiles from the FTP site, mosaic the tiles into one seamless raster, and then fill NoData gaps through interpolation. I describe the details of the tool further in the blog linked here. I find that it helps to speed up the workflow when you're dealing with quite large numbers of SRTM tiles. For example, here is a 90 m SRTM seamless mosaic DEM of the British Isles, which took less than five minutes to create, including the download time of the 91 individual .hgt files.

enter image description here

The tool will be publicly released with version 3.2.1 of Whitebox GAT, but it can be retrieved from the Whitebox repository now if you're interested in a preview (follow the link in the blog).

enter image description here

UPDATE

I've just publicly released the latest version of the software, which includes the SRTM data downloader tool described in this post.

  • Wow - looks great. Unfortunately already started my download with wget and a regular expression. Going on right now. If I knew 3 hours earlier I would have used this. – gansub Sep 13 '14 at 15:32
  • @user311554 No problem, hopefully my answer can help others out as well. – WhiteboxDev Sep 13 '14 at 15:36
  • @user311554 Just to let you know that the SRTM download tool is now publicly available in v. 3.2.1 of Whitebox. – WhiteboxDev Sep 18 '14 at 19:05

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