It ain't pretty or efficient, but it's cheap. Here's min value. Remove
'r' from sort for max value:
gdal2xyz.py -csv -skipnodata source.tif /dev/stdout | grep -v done |
sort -rnk 3,3 -t "," | tail -1
result:
-116.9916667,36.54166667,46
On 10/29/24 17:31, Rahkonen Jukka via gdal-dev wrote:
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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