[gdal-dev] How to locate where the raster min and max values are?

[Rahkonen Jukka]

Hi,

I would like to know the georeferenced coordinates of the min and max values of a DEM file. Even better if I could forward them into a vector file. If the minimum or maximum happens to be on a flat area like seabed I would be happy with the first pixel at the moment.

By copy-pasting from How do I open geotiff images with GDAL in Python? - Stack Overflow<https://stackoverflow.com/questions/41996079/how-do-i-open-geotiff-images-with-gdal-in-python> and How to find the indexes of the minimum or maximum value(s) in a matrix using python ?<https://en.moonbooks.org/Articles/How-to-find-the-indexes-of-the-minimum-or-maximum-values-in-a-matrix-using-python-/> I think I managed to get the correct points as numpy indexes

>>> import numpy as np
>>> from osgeo import gdal
>>> ds = gdal.Open('P3412A.tif', gdal.GA_ReadOnly)
>>> rb = ds.GetRasterBand(1)
>>> img_array = rb.ReadAsArray()
>>> vmin = img_array.min()
>>> vmax = img_array.max()
>>> vmin
-0.929
>>> vmax
17.246
>>>
>>> np.where(img_array==vmin)
(array([1504], dtype=intg64), array([1189], dtype=int64))
>>> np.where(img_array==vmax)
(array([1545], dtype=int64), array([2423], dtype=int64))
>>>

But now I have no idea about how to get the georeferenced coordinates.
The task feels rather simple and I was sure that someone has already made an utility or a QGIS plugin, but all I have found yet is for R. I was thinking that perhaps some of the gdaldem modes could be misused for this purpose, but I believe they cannot. For QGIS I found advice to use an obvious but  clumsy method of polygonising the raster and finding the extremes from the vector data. And one OpenJUMP developer took the challenge and wrote a prototype with Java but it is not complete yet.

-Jukka Rahkonen-
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