r.geomorphon: Put the FORMS enum right

Dàibhidh Grannd (English Language and Linguistics, School of Critical
Studies, University of Glasgow) points out that in the plugin HTML
documentation and in the original paper landform category 5 stands for
"SP" (spur), not "CV" (convex slope), and landform category 7 stands
for "HL" (hollow), not "CN" (concave slope). Amend that in the code and
update the comments.

Use the type where it belongs and replace a number of hard-coded
constants with enumeration constants. Reduce a variable scope.

raster/r.geomorphon/geom.c

@@ -44,7 +44,7 @@ unsigned int ternary_rotate(unsigned int value)
     return code < rev_code ? code : rev_code;
 }
 
-int determine_form(int num_minus, int num_plus)
+FORMS determine_form(int num_minus, int num_plus)
 {
     /* determine form according number of positives and negatives
      * simple approach to determine form pattern */
@@ -54,28 +54,16 @@ int determine_form(int num_minus, int num_plus)
 	/*       0   1   2   3   4   5   6   7   8  */
 	/* 0 */ {FL, FL, FL, FS, FS, VL, VL, VL, PT},
 	/* 1 */ {FL, FL, FS, FS, FS, VL, VL, VL, __},
-	/* 2 */ {FL, SH, SL, SL, CN, CN, VL, __, __},
-	/* 3 */ {SH, SH, SL, SL, SL, CN, __, __, __},
-	/* 4 */ {SH, SH, CV, SL, SL, __, __, __, __},
-	/* 5 */ {RI, RI, CV, CV, __, __, __, __, __},
+	/* 2 */ {FL, SH, SL, SL, HL, HL, VL, __, __},
+	/* 3 */ {SH, SH, SL, SL, SL, HL, __, __, __},
+	/* 4 */ {SH, SH, SP, SL, SL, __, __, __, __},
+	/* 5 */ {RI, RI, SP, SP, __, __, __, __, __},
 	/* 6 */ {RI, RI, RI, __, __, __, __, __, __},
 	/* 7 */ {RI, RI, __, __, __, __, __, __, __},
 	/* 8 */ {PK, __, __, __, __, __, __, __, __},
     };
+    /* (See the FORMS enum for the legend.) */
 
-    /* legend:
-       FL,  flat
-       PK,  peak, summit
-       RI,  ridge
-       SH,  shoulder
-       CV,  convex
-       SL,  slope
-       CN,  concave
-       FS,  footslope
-       VL,  valley
-       PT,  pit, depression
-       __  error, impossible
-     */
     return forms[num_minus][num_plus];
 }
 

raster/r.geomorphon/local_proto.h

@@ -100,16 +100,16 @@ typedef enum
 {
     ZERO,			/* zero cats do not accept zero category */
     FL,				/* flat */
-    PK,				/* peak, summit */
+    PK,				/* peak (summit) */
     RI,				/* ridge */
     SH,				/* shoulder */
-    CV,				/* convex slope */
+    SP,				/* spur (convex slope) */
     SL,				/* slope */
-    CN,				/* concave slope */
+    HL,				/* hollow (concave slope) */
     FS,				/* footslope */
     VL,				/* valley */
-    PT,				/* pit, depression */
-    __,				/* error */
+    PT,				/* pit (depression) */
+    __,				/* error (impossible) */
     CNT				/* counter */
 } FORMS;
 
@@ -158,7 +158,7 @@ int write_contrast_colors(char *);
 /* geom */
 int calc_pattern(PATTERN * pattern, int row, int cur_row, int col);
 unsigned int ternary_rotate(unsigned int value);
-int determine_form(int num_plus, int num_minus);
+FORMS determine_form(int num_plus, int num_minus);
 int determine_binary(int *pattern, int sign);
 int determine_ternary(int *pattern);
 int rotate(unsigned char binary);

raster/r.geomorphon/main.c

@@ -66,9 +66,9 @@ int main(int argc, char **argv)
 	{PK, 56, 0, 0, "summit"},
 	{RI, 200, 0, 0, "ridge"},
 	{SH, 255, 80, 20, "shoulder"},
-	{CV, 250, 210, 60, "spur"},
+	{SP, 250, 210, 60, "spur"},
 	{SL, 255, 255, 60, "slope"},
-	{CN, 180, 230, 20, "hollow"},
+	{HL, 180, 230, 20, "hollow"},
 	{FS, 60, 250, 150, "footslope"},
 	{VL, 0, 0, 255, "valley"},
 	{PT, 0, 0, 56, "depression"},
@@ -371,7 +371,7 @@ int main(int argc, char **argv)
 		    continue;
 		}		/* end null value */
 		{
-		    int cur_form, small_form;
+		    FORMS cur_form;
 
 		    search_distance = search_dist;
 		    skip_distance = skip_dist;
@@ -386,8 +386,9 @@ int main(int argc, char **argv)
 		    /* correction of forms */
 		    if (extended && search_distance > 10 * max_resolution) {
 			/* 1) remove extensive innatural forms: ridges, peaks, shoulders and footslopes */
-			if ((cur_form == 4 || cur_form == 8 || cur_form == 2
-			     || cur_form == 3)) {
+			if ((cur_form == SH || cur_form == FS || cur_form == PK
+			     || cur_form == RI)) {
+			    FORMS small_form;
 			    search_distance =
 				(search_dist / 2. <
 				 4 * max_resolution) ? 4 *
@@ -400,9 +401,9 @@ int main(int argc, char **argv)
 			    small_form =
 				determine_form(pattern->num_negatives,
 					       pattern->num_positives);
-			    if (cur_form == 4 || cur_form == 8)
-				cur_form = (small_form == 1) ? 1 : cur_form;
-			    if (cur_form == 2 || cur_form == 3)
+			    if (cur_form == SH || cur_form == FS)
+				cur_form = (small_form == FL) ? FL : cur_form;
+			    if (cur_form == PK || cur_form == RI)
 				cur_form = small_form;
 			}
 			/* 3) Depressions */

raster/r.geomorphon/memory.c

@@ -104,18 +104,18 @@ int write_form_cat_colors(char *raster, CATCOLORS * ccolors)
 {
     struct Colors colors;
     struct Categories cats;
-    int i;
+    FORMS i;
 
     Rast_init_colors(&colors);
 
-    for (i = 1; i < CNT; ++i)
+    for (i = FL; i < CNT; ++i)
 	Rast_add_color_rule(&ccolors[i].cat, ccolors[i].r, ccolors[i].g,
 			    ccolors[i].b, &ccolors[i].cat, ccolors[i].r,
 			    ccolors[i].g, ccolors[i].b, &colors, CELL_TYPE);
     Rast_write_colors(raster, G_mapset(), &colors);
     Rast_free_colors(&colors);
     Rast_init_cats("Forms", &cats);
-    for (i = 1; i < CNT; ++i)
+    for (i = FL; i < CNT; ++i)
 	Rast_set_cat(&ccolors[i].cat, &ccolors[i].cat, ccolors[i].label,
 		     &cats, CELL_TYPE);
     Rast_write_cats(raster, &cats);