v.to.3d: make reverse transformation possible also for lines - contours

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@65493 15284696-431f-4ddb-bdfa-cd5b030d7da7

vector/v.to.3d/trans3.c

@@ -105,7 +105,7 @@ void trans3d(struct Map_info *In, struct Map_info *Out, int type,
 			"Using category %d."), line, cat);
 	}
 
-	if (zcolumn && ltype == GV_POINT && cat > -1) {
+	if (zcolumn && ltype & (GV_POINT | GV_LINE) && cat > -1) {
 	    /* category exist in table ? */
 	    cex = (int *)bsearch((void *)&cat, cats, ncats, sizeof(int),
 				 srch);

vector/v.to.3d/v.to.3d.html

@@ -14,6 +14,11 @@ features can be optionally stored in <b>column</b>.
 
 When transforming 2D vector features to 3D based on attribute, all
 NULL values are silently converted to height 0.0.
+<p>
+Reverse transformation is possible for points and lines.
+In case of lines, the reverse transformation should be used
+only when all vertices of a line have the same z-coordinate
+(for example contours).
 
 <h2>EXAMPLES</h2>