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<p class="MsoNormal">Hi,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span lang="EN-US">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.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">By copy-pasting from </span><a href="https://stackoverflow.com/questions/41996079/how-do-i-open-geotiff-images-with-gdal-in-python"><span lang="EN-US">How do I open geotiff images with GDAL in Python? - Stack Overflow</span></a>
<span lang="EN-US">and </span><a href="https://en.moonbooks.org/Articles/How-to-find-the-indexes-of-the-minimum-or-maximum-values-in-a-matrix-using-python-/"><span lang="EN-US">How to find the indexes of the minimum or maximum value(s) in a matrix using python
?</span></a> <span lang="EN-US">I think I managed to get the correct points as numpy indexes<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">>>> import numpy as np<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">>>> from osgeo import gdal<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">>>> ds = gdal.Open('P3412A.tif', gdal.GA_ReadOnly)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">>>> rb = ds.GetRasterBand(1)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">>>> img_array = rb.ReadAsArray()<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">>>> vmin = img_array.min()<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">>>> vmax = img_array.max()<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">>>> vmin<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">-0.929<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">>>> vmax<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">17.246<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">>>><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">>>> np.where(img_array==vmin)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">(array([1504], dtype=intg64), array([1189], dtype=int64))<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">>>> np.where(img_array==vmax)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">(array([1545], dtype=int64), array([2423], dtype=int64))<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">>>><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">But now I have no idea about how to get the georeferenced coordinates.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">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.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">-Jukka Rahkonen-<o:p></o:p></span></p>
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