add gnomonic projection and its inverse

also: doc: presently, the area function requires convex polygons

Author: Markus Nullmeier

Makefile

@@ -2,13 +2,13 @@ MODULE_big = pg_sphere
 OBJS       = sscan.o sparse.o sbuffer.o vector3d.o point.o \
              euler.o circle.o line.o ellipse.o polygon.o \
              path.o box.o output.o gq_cache.o gist.o key.o \
-             crossmatch.o
+             crossmatch.o gnomo.o
 
 EXTENSION   = pg_sphere
 DATA_built  = pg_sphere--1.0.sql
 DOCS        = README.pg_sphere COPYRIGHT.pg_sphere
 REGRESS     = init tables points euler circle line ellipse poly path box index \
-              contains_ops contains_ops_compat bounding_box_gist
+              contains_ops contains_ops_compat bounding_box_gist gnomo
 
 EXTRA_CLEAN = pg_sphere--1.0.sql $(PGS_SQL) 
 
@@ -18,7 +18,7 @@ CRUSH_TESTS  = init_extended circle_extended
 PGS_SQL    =  pgs_types.sql pgs_point.sql pgs_euler.sql pgs_circle.sql \
    pgs_line.sql pgs_ellipse.sql pgs_polygon.sql pgs_path.sql \
    pgs_box.sql pgs_contains_ops.sql pgs_contains_ops_compat.sql \
-   pgs_gist.sql pgs_crossmatch.sql \
+   pgs_gist.sql pgs_crossmatch.sql gnomo.sql \
 
 ifdef USE_PGXS
   ifndef PG_CONFIG

doc/functions.sgm

@@ -14,8 +14,8 @@
             <para>
               The <function>area</function> function returns the area of a
               spherical object in square radians. Supported data types are:
-              <type>scircle</type>, <type>spolygon</type>, and
-              <type>sbox</type>.
+              <type>scircle</type>, <type>spolygon</type> (if the polygon
+	      is convex), and <type>sbox</type>.
             </para>
             <example>
               <title>Area of a spherical circle as a multiple of &pgr;</title>