* Rich Shepard <[email protected]> [2018-01-26 11:12:14 -0800]:
On Fri, 26 Jan 2018, Nikos Alexandris wrote:how can we compute the median of a floating point cover raster map, over a base map (using the conventional terminology as in r.stats.zonal)?Nikos, By definition the median value has as many observations/measurements less than this value as greater than this value. Because floating point numbers are not represented exactly in computers (unless you extend them out to several dozen digits to the right of the decimal point), I suggest you create a map with integer values that will work for your application.
Something like multiply by * 1000, find the median, then divide by 1000 (as suggested in the past for other modules that don't treat fp numbers).
You can find cells with values greater than some number, and less than some number but you'll have a difficult time finding that number and getting grass (or any application) to recognize it.
HTH,
Yes it helps. As for the last comment: do you mean it's going to be computationally "difficult", as in running time? There are algorithms that handle this as I read on the net. If floating point numbers of the cover map that fall inside an area (as per the base map), are treated as a vector, then sorting the figures will give an answer. Even in case of even number of numbers, the median can be, practically, the average of the two middle-placed figures, or select the highest number of the lower part. Thank you, Nikos
signature.asc
Description: PGP signature
_______________________________________________ grass-user mailing list [email protected] https://lists.osgeo.org/mailman/listinfo/grass-user
