I am trying to work with some GeoTiffs downloaded from OpenTopography.

I need to know the x dimension and y dimension of the region extracted in units, for example meters, but I do not know how to get those from the values OpenTopography provides:

Xmin = -63.080749511718736 Ymin = -38.666854934630194 Xmax = -61.00982666015623 Ymax = -37.28126487387608

Maybe there is a way to convert those to unit dimension using Qgis?

  • 1
    Is the CRS of the GeoTiffs WGS 84? Your X and Y values are in decimal degrees if so. You may need to reproject your data to a projected coordinate system to get values in metres. – Dirwin Aug 21 at 15:33
  • Horizontal Coordinates: WGS 1984 [EPSG: 4326]. Vertical Coordinates: WGS84. How would I got about doing that? I am really new with this kind of stuff. – ShynnSup Aug 21 at 15:40

To reproject your data to a projected coordinate system:

  1. Load you GeoTIFF into QGIS and right-click on this layer in the 'layers' panel. Select Export > Save As...
  2. In the window which appears, set Format to GeoTIFF, set your filename and pick a suitable projected coordinate system for your CRS. I'm not sure where in the world your data is so I can't recommend the exact one to use.
  3. Click OK and load the new GeoTIFF into your project. Right-click on this layer in the 'layers' panel and select Properties...
  4. Select the 'Information' tab and your units should now be in metres/feet etc. Multiply width (i.e. number of pixels) by the pixel size to find the total width of your GeoTIFF in your desired units.
  • Hi, thank you! My data is located in Argentina, Buenos Aires province. – ShynnSup Aug 21 at 20:27
  • 1
    You could try using UTM CRS. You can use the map at dmap.co.uk/utmworld.htm to find your UTM zone, I think you're in 21 so the WGS 84 / UTM zone 21S EPSG:32721 CRS should work. – Dirwin Aug 22 at 7:23

If your data is really a GeoTiff then all the information you need will be buried in the file's metadata. Add your GeoTiff to QGIS. Open the Layer Properties and select the Information tab. This will open a window and show you the coordinate reference system of these data, the extents, units of measure, and pixel size of these data. As Dirwin points out, you may need to reproject your data if you are interested in these values in meters.

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You may have a TIFF that is not a GeoTiff in that the coordinate reference system (CRS)information is not contained in the Tiff but stored in a world file. The world file will have the same name as the Tiff but with a TFW extension. If this is the case you can open the TFW using a text reader. Some detective work may be required to determine the CRS of your data. Below is an example of a world file that references WGS84 with units in lat/long.

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