[GRASS-user] r.mfilter produces empty result

[Luí­s Moreira de Sousa]

Dear all,

I am trying to apply a high pass filter to a raster; following [Markus Neteler's book](https://books.google.ch/books?id=G20ECAAAQBAJ&pg=PA245&lpg=PA245&dq=grass+image+processing+high+pass+filter&source=bl&ots=2vRjTedatC&sig=d9v0nBMNVeysasmNs5YeZxn9D8Y&hl=en&sa=X&redir_esc=y#v=onepage&q=grass%20image%20processing%20high%20pass%20filter&f=false) I created a simple high-pass filter:

> cat highpass9.txt
TITLE 3x3 High Pass
MATRIX 3
-1 -1 -1
-1  8 -1
-1 -1 -1
DIVISOR 9
TYPE S

I then apply the filter:

> r.mfilter input=blenddem output=blenddem.highpass filter=highpass9.txt
 100%
Writing raster map <blenddem.highpass>

Apparently everything went fine, but in the Map Display the resulting raster is entirely blank.

A quick check with the statistics shows that indeed the result is empty:

> r.univar blenddem.highpass
 100%

What is going on here? I also tried the same filter in Markus' book and result is again a blank raster. Is there some operation missing?

More details on this issue at GIS.SE: https://gis.stackexchange.com/q/239556/21532

Thank you.

--
Luís Moreira de Sousa
Im Grund 6
CH-8600 Dübendorf
Switzerland

Phone: +41 (0)79 812 62 65
Email: luis.de.sousa at protonmail.ch
URL: https://sites.google.com/site/luismoreiradesousa
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