[GRASSLIST:7010] Re: calculating center of intensity

Hamish hamish_nospam at yahoo.com
Sat Jun 4 00:39:24 EDT 2005

> >> Does anyone know of a way to calculate the center of a shape in a  
> >> raster file based on shape and pixel values?  For example, imagine 
> >> a NEXRAD RADAR image showing a storm cloud.  Could GRASS be used  
> >> to calculate the center of the cloud?  I'm not having any luck  
> >> finding a grass raster function to do this.
> Thanks for the response.  By center, I did not mean the geometric  
> centroid, rather the center of intensity based on pixel values.
> I have worked with folks in the Geography department, and I know that 
> this sort of thing is relatively easy mathematically, I just wanted  
> to know if it was possible with GRASS 6.0 as it is.

View intensity as elevation and find the peaks.

e.g. visualize it in NVIZ.

Along that line of thought you can use the 'r.param.scale param=feature'
GRASS command to pull out the morphometric features: peaks, ridges,
passes, channels, pits and planes.

Or use r.slope.aspect to determine slope and curvature (1st & 2nd
derivatives) and find areas of no slope with negative curvature.

You'll then have to reclass your clouds to make them somewhat coherent,
and then label each distinct cloud with a max value taken from the area
of the peak in the orginial. If you want this last part to be automated
it might take some work, but I would think it is possible.


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