Given a topographic raster image.
Given a pixel's coordinate in pixel/lines or geocoordinate.
How to get it's pixel value ?
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1. Get the pixels value: gdal's
gdallocationinfo allow to access a pixel's value.
The gdallocationinfo utility provide a mechanism to query information about a pixel given it's location in one of a variety of coordinate systems. Several reporting options are provided.
$ gdallocationinfo crop.tif 50 50 Report: Location: (50px,50line) Band 1: Value: 73
To only get the value :
$ gdallocationinfo crop.tif 50 50 -valonly > 73
Depending on geocoordinate:
$ gdallocationinfo crop.tif -geoloc 0.00 44.00 > 132
Afterwhat you may want to 1. iterate all pixels and 2. apply conditional filter.