v.overlay: snap by default with 1e-8

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@53994 15284696-431f-4ddb-bdfa-cd5b030d7da7

vector/v.overlay/main.c

@@ -127,7 +127,7 @@ int main(int argc, char *argv[])
     snap_opt->label = _("Snapping threshold for boundaries");
     snap_opt->description = _("Disable snapping with snap <= 0");
     snap_opt->type = TYPE_DOUBLE;
-    snap_opt->answer = "0";
+    snap_opt->answer = "1e-8";
 
     table_flag = G_define_standard_flag(G_FLG_V_TABLE);
 

vector/v.overlay/v.overlay.html

@@ -8,10 +8,12 @@ oerator.
 If areas in <em>ainput</em> are overlaid with areas in <em>binput</em>, 
 it is sometimes necessary to snap areas of <em>binput</em> to those of 
 <em>ainput</em>, otherwise areas can go missing or many sliver areas 
-can be created. Snapping can be enabled by setting the <em>snap</em> 
-option to a value larger zero. Recommended are values between 
-0.00000001 and 0.0001. Using larger values for snapping can have 
-undesired side-effects.
+can be created. Snapping is enabled by default and can be disabled by 
+setting the <em>snap</em> option to a negative value. Recommended values 
+are between 0.00000001 and 0.0001. Using larger values for snapping can 
+have undesired side-effects. Snapping modifies only boundaries in binput, 
+which are snapped to boundaries in ainput. Boundaries in ainput are not 
+modified.
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