Change r.thin documentation to match module behaviour introduced in https://trac.osgeo.org/grass/changeset/44866

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@65083 15284696-431f-4ddb-bdfa-cd5b030d7da7

raster/r.thin/main.c

@@ -56,7 +56,7 @@ int main(int argc, char *argv[])
     G_add_keyword(_("raster"));
     G_add_keyword(_("geometry"));
     module->description =
-	_("Thins non-zero cells that denote linear "
+	_("Thins non-null cells that denote linear "
 	  "features in a raster map layer.");
 
     opt1 = G_define_standard_option(G_OPT_R_INPUT);

raster/r.thin/r.thin.html

@@ -1,13 +1,13 @@
 <h2>DESCRIPTION</h2>
 
 <em>r.thin</em> scans the named <em>input</em> raster map layer and 
-thins non-zero cells that denote linear features into linear features 
+thins non-null cells that denote linear features into linear features 
 having a single cell width. Raster lines often need to be thinned 
 (skeletonizing raster features) to a single pixel width before they can 
 be transformed to vector data.
 
 <p>
-<em>r.thin</em> will thin only the non-zero cells of the
+<em>r.thin</em> will thin only the non-null cells of the
 named <em>input</em> raster map layer within the current
 geographic region settings.  The cell width of the thinned
 <em>output</em> raster map layer will be equal to the cell
@@ -19,9 +19,11 @@ cell.
 <em>r.thin</em> will create a new <em>output</em> raster
 data file containing the thinned linear features.
 <em>r.thin</em> assumes that linear features are encoded
-with positive values on a background of 0's in the
-<em>input</em> raster data file, hence it creates a 0/1
+with positive values on a background of null's in the
+<em>input</em> raster data file, hence it creates a null/1
 output map.
+Note - behaviour of <em>r.thin</em> was changed in GRASS 7 to
+use null instead of 0 for input and output.
 
 <h2>NOTES</h2>