v.overlay: improve description, keywords, examples

git-svn-id: https://svn.osgeo.org/grass/grass/branches/releasebranch_7_0@68943 15284696-431f-4ddb-bdfa-cd5b030d7da7

vector/v.overlay/main.c

@@ -62,10 +62,11 @@ int main(int argc, char *argv[])
     G_add_keyword(_("vector"));
     G_add_keyword(_("geometry"));
     G_add_keyword(_("spatial query"));
+    G_add_keyword(_("clip"));
+    G_add_keyword(_("difference"));
     G_add_keyword(_("intersection"));
     G_add_keyword(_("union"));
-    G_add_keyword(_("clip"));
-    module->description = _("Overlays two vector maps.");
+    module->description = _("Overlays two vector maps offering clip, intersection, difference, symmetrical difference, union operators.");
 
     in_opt[0] = G_define_standard_option(G_OPT_V_INPUT);
     in_opt[0]->label = _("Name of input vector map (A)");
@@ -113,8 +114,9 @@ int main(int argc, char *argv[])
 	       "and;%s;or;%s;not;%s;xor;%s",
 	       _("also known as 'intersection' in GIS"),
 	       _("also known as 'union' in GIS (only for atype=area)"),
-	       _("features from ainput not overlayed by features from binput"),
-	       _("features from either ainput or binput but "
+	       _("also known as 'difference' (features from ainput not "
+                 "overlayed by features from binput)"),
+	       _("also known as 'symmetrical difference' (features from either ainput or binput but "
 		 "not those from ainput overlayed by binput (only "
 		 "for atype=area)"));
     operator_opt->descriptions = desc;

vector/v.overlay/v.overlay.html

@@ -97,6 +97,8 @@ d.mon wx0
 
 <h3>AND operator</h3>
 
+Clipping example (no attribute table is generated here):
+
 <div class="code"><pre>
 d.vect map=zipcodes_wake fill_color=0:128:0
 d.vect map=box fill_color=85:130:176
@@ -112,6 +114,8 @@ v.overlay with AND operator (selected polygons in grey color)
 
 <h3>OR operator</h3>
 
+Union example of areas:
+
 <div class="code"><pre>
 d.vect map=zipcodes_wake fill_color=0:128:0
 d.vect map=box fill_color=85:130:176
@@ -127,6 +131,8 @@ v.overlay with OR operator (selected polygons in grey color)
 
 <h3>XOR operator</h3>
 
+Symmetrical difference example:
+
 <div class="code"><pre>
 d.vect map=zipcodes_wake fill_color=0:128:0
 d.vect map=box fill_color=85:130:176
@@ -142,6 +148,8 @@ v.overlay with XOR operator (selected polygons in grey color)
 
 <h3>NOT operator</h3>
 
+Difference example:
+
 <div class="code"><pre>
 d.vect map=zipcodes_wake fill_color=0:128:0
 d.vect map=box fill_color=85:130:176
@@ -157,7 +165,7 @@ v.overlay with NOT operator (selected polygon in grey color)
 
 <h3>Overlay operations: AND, OR, NOT, XOR</h3>
 
-Examples based on North Carolina sample dataset:
+ZIP code examples, based on North Carolina sample dataset:
 
 <div class="code"><pre>
 # creation of simple dataset