GeoTIFFs made in GDAL don't have min/max range when loaded in Arc/QGIS

Question

I'm creating some floating point rasters in GDAL with the GeoTIFF driver. When I load the resulting images into QGIS or Arc the default symbology puts the min at -3.40282e38 and max to 3.40282e38, so the raster looks exactly gray. Is there a way I can write the actual range into the GeoTIFF directly so when its loaded into a GIS program it automatically scales the histogram nicely? I've tried creating a default histogram like this:

rasterMin, rasterMax = raster.GetRasterBand(1).ComputeRasterMinMax()
raster.GetRasterBand(1).SetDefaultHistogram(rasterMin, rasterMax, 255)

But I get a error that looks like a binding issue:

  File "/usr/lib/python2.6/dist-packages/osgeo/gdal.py", line 846, in SetDefaultHistogram
    return _gdal.Band_SetDefaultHistogram(self, *args)
TypeError: not a sequence

Any suggestions on what I could do, or if I've made a mistake?

Answer 1

If you're generating the data, then you can keep track of the min and max on the fly. If you don't have direct control of the source data, say if you are compositing existing data, then using ComputeRasterMinMax(0) is fine.

Either way, after you've got your min and max values, you should call SetStatistics() on the band, and ensure you set your dataset to None when you've finished to ensure everything gets written to disk.

Also, something in the back of my mind is telling me using dataset.GetRasterBand(1).<some band function> won't work properly because of the way GDAL Python handles band references. I can't remember the details, but there was something on the GDALDev mailing list some time ago. So it's best to create a band variable explicitly: band = dataset.GetRasterBand(1), then call band.SetStatistics(min, max, mean, stddev).

Answer 2

I'm not aware of a way to do it using GDAL, but you can use python to call the 'calculate statistics' tool in Arc.

Answer 3

gdalinfo -mm -stats

Will calculate the stats