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I have a set of GeoTIFF files which I have generated from the MODIS LST Product and have used the coordinate information present within the file to work out the index of my 'pixel of interest'/study site. My aim is to extract the data value at this index and so far have been using this code within python:

myfile = band.ReadAsArray(0, 0, cols, rows)
value = myfile[y_index, x_index]

which works just fine. This generates the result I want but I am having to read in the whole data file first, before obtaining the result I require. Is it possible to read just my 'pixel of interest' or a subset of the data without having to read the whole file into memory beforehand?

I am using Python and the gdal module within it.

  • For sure it is possible. Probably you want to use ReadBlock gdal.org/… If you want fast access to a subset you must use tiffs which are written as tiled. – user30184 Oct 24 '16 at 14:16
  • Thanks for your reply, I have added a solution to this question below using the method I had already stated, I was trying to make things more complicated than need be! Overthinking strikes again! – tda Oct 24 '16 at 14:22
  • You may want to study and compare how the special GDAL tool "gdallocationinfo" does the job trac.osgeo.org/gdal/browser/trunk/gdal/apps/…. – user30184 Oct 24 '16 at 14:29
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I was trying to make things more complicated than they needed to be, one simple solution is as follows:

When using ReadAsArray(), the function works as follows:

data = myfile.ReadAsArray(x_offset, y_offset, x_size, y_size)

So if you use:

data = myfile.ReadAsArray(x_index, y_index, 1, 1)

This will read in JUST one pixel.

But the code can be adapted to read in a 3x3 window etc. using:

data = myfile.ReadAsArray(x_index - 1, y_index - 1, 3, 3)

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