Hi,
See https://github.com/OSGeo/gdal/pull/11200 for an API and sample
script to offer that capability (that can scale to datasets that don't
fit in RAM)
Even
Le 30/10/2024 à 01:31, Rahkonen Jukka via gdal-dev a écrit :
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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