[GIS] From tiff file extract values with QGIS

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I have download a tiff file with elevation from http://srtm.csi.cgiar.org/SELECTION/inputCoord.asp and I try to export in file text or Excel the coordinates and the elevation and I don't know how to export this data in text file.

Best Answer

Using QGIS select Raster/Conversion/Translate (Convert format) ... from the menu. Select the ASCII Gridded XYZ file type and set the output file. It will execute a gdal_translate command as you can see it in the dialog. gdal_translate -of XYZ input.tif output.xyz

Note: it will use the raster value of the first band as Z value if you have a multiband image (e.g. RGB).

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[GIS] Convert .asc format into shapefile

You can try the GDAL utility gdal_polygonize.py. For example, to create a shapefile output.shp from input.asc:

gdal_polygonize.py -f "ESRI Shapefile" input.asc output.shp

Prerequisites: GDAL, Python and GDAL Python bindings.

But... Are you sure that SHP is the right format in order to work with such huge data?

[GIS] Exporting QGIS contour attributes in DXF file

When you generate the contours in QGIS, make sure that you tick the Attribute name box. Then when you ogr2ogr (you must use command line - this is not an option in QGIS Save AS), specify the zfield. For example, if your elevation attribute is "ELEV", then your command could look something this:

ogr2ogr -f "DXF" contours-out.dxf contours.shp -zfield ELEV

By the way, if you were searching for this in answers, you would not have found it. I learned this method from this question.

EDIT: I should also point out that the DXF will not have an attribute field for elevation, but instead will be drawn to elevation.

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