X-Git-Url: http://pileus.org/git/?a=blobdiff_plain;f=src%2Fgis-util.c;h=587dd5c10d26e3418a1d80b0ef6c282d37117011;hb=d1e2d70c4f601f09d2df0f728a6ea4eb1c12f8de;hp=3bd5246002e134843c7c8c2a13726dbc8e05c653;hpb=a2a902d978b6050289f7a92794fb1dc0aa2b5e26;p=grits

diff --git a/src/gis-util.c b/src/gis-util.c
index 3bd5246..587dd5c 100644
--- a/src/gis-util.c
+++ b/src/gis-util.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2009 Andy Spencer <spenceal@rose-hulman.edu>
+ * Copyright (C) 2009-2010 Andy Spencer <andy753421@gmail.com>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -15,6 +15,59 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+/**
+ * SECTION:gis-util
+ * @short_description: Geographic utilities
+ *
+ * Miscellaneous utility functions, these deal mostly with coordinate
+ * conversion. Below are some examples that should help demonstrate how these
+ * functions work.
+ *
+ * <example>
+ * <title>Terminology</title>
+ * <programlisting>
+ * deg    - Degrees
+ * rad    - Radians, also radius
+ * m      - Meters, for earth-based distances
+ * px     - Pixels, for screen-based distances
+ *
+ * height - Height, the distance above the geoid (ground)
+ * elev   - Elevation, the distance above the spheroid
+ * rad    - Radius, the distance from the center of the earth
+ *
+ * lat    - Latitude, amount north-south, -90 (S) .. 90 (N)
+ * lon    - Longitude, amount east-west, -180 (W) .. 180 (E)
+ * incl   - Inclination, polar equiv of  latitude, Pi .. 0
+ * azim   - Azimuth, polar equiv of longitude, -Pi .. Pi
+ *
+ * x      -  0° lon is positive
+ * y      - 90° lon is positive
+ * z      - North pole is positive
+ *
+ * llh    - lat,lon,height
+ * lle    - lat,lon,elev
+ * llr    - lat,lon,rad
+ * pol    - incl,azim,rad
+ * xyz    - x,y,z
+ * </programlisting>
+ * </example>
+ *
+ * <example>
+ * <title>Conversions</title>
+ * <programlisting>
+ *             lat    lon   elev ->      x      y      z
+ * lle2xyz:    0.0,   0.0,   0.0 ->    0.0,   0.0,  10.0
+ * lle2xyz:   90.0,   0.0,   0.0 ->    0.0,  10.0,   0.0
+ * lle2xyz:    0.0,  90.0,   0.0 ->   10.0,   0.0,   0.0
+ *
+ *               x      y      z ->    lat    lon   elev
+ * xyz2lle:   10.0,   0.0,   0.0 ->    0.0,  90.0,   0.0
+ * xyz2lle:    0.0,  10.0,   0.0 ->   90.0,   0.0,   0.0
+ * xyz2lle:    0.0,   0.0,  10.0 ->    0.0,   0.0,   0.0
+ * </programlisting>
+ * </example>
+ */
+
 #include <glib.h>
 #include <math.h>
 
@@ -23,6 +76,18 @@
 /******************
  * Global helpers *
  ******************/
+/**
+ * lle2xyz:
+ * @lat:  the latitude
+ * @lon:  the longitude
+ * @elev: the elevation
+ * @x:    the resulting x coordinate
+ * @y:    the resulting y coordinate
+ * @z:    the resulting z coordinate
+ *
+ * Convert a point from latitude, longitude, and elevation to x, y and z
+ * coordinates.
+ */
 void lle2xyz(gdouble lat, gdouble lon, gdouble elev,
 		gdouble *x, gdouble *y, gdouble *z)
 {
@@ -34,6 +99,18 @@ void lle2xyz(gdouble lat, gdouble lon, gdouble elev,
 	*y = rad * cos(incl);
 }
 
+/**
+ * xyz2lle:
+ * @x:    the x coordinate
+ * @y:    the y coordinate
+ * @z:    the z coordinate
+ * @lat:  the resulting latitude
+ * @lon:  the resulting longitude
+ * @elev: the resulting elevation
+ *
+ * Convert a point from x, y and z coordinates to latitude, longitude, and
+ * elevation.
+ */
 void xyz2lle(gdouble x, gdouble y, gdouble z,
 		gdouble *lat, gdouble *lon, gdouble *elev)
 {
@@ -43,6 +120,16 @@ void xyz2lle(gdouble x, gdouble y, gdouble z,
 	*elev = rad2elev(rad);
 }
 
+/**
+ * xyz2ll:
+ * @x:    the x coordinate
+ * @y:    the y coordinate
+ * @z:    the z coordinate
+ * @lat:  the resulting latitude
+ * @lon:  the resulting longitude
+ *
+ * Get the latitude and longitude for a x, y, z value.
+ */
 void xyz2ll(gdouble x, gdouble y, gdouble z,
 		gdouble *lat, gdouble *lon)
 {
@@ -51,6 +138,15 @@ void xyz2ll(gdouble x, gdouble y, gdouble z,
 	*lon = azim2lon(atan2(x,z));
 }
 
+/**
+ * ll2m:
+ * @lon_dist: the distance in degrees of longitude
+ * @lat:      the latitude to calculate at
+ *
+ * Calculate the distance of longitudinal span at a particular latitude. 
+ *
+ * Returns: the distance in meters
+ */
 gdouble ll2m(gdouble lon_dist, gdouble lat)
 {
 	gdouble azim = (-lat+90)/180*M_PI;
@@ -59,9 +155,41 @@ gdouble ll2m(gdouble lon_dist, gdouble lat)
 	return lon_dist/360 * circ;
 }
 
+/**
+ * distd:
+ * @a: the first point
+ * @b: the second point
+ *
+ * Calculate the distance between two three dimensional points.
+ *
+ * Returns: the distance between the points
+ */
 gdouble distd(gdouble *a, gdouble *b)
 {
 	return sqrt((a[0]-b[0])*(a[0]-b[0]) +
 	            (a[1]-b[1])*(a[1]-b[1]) +
 	            (a[2]-b[2])*(a[2]-b[2]));
 }
+
+/**
+ * lon_avg:
+ * @a: the first longitude
+ * @b: the second longitude
+ *
+ * Calculate the average longitude between two longitudes. This is smart about
+ * which side of the globe the resulting longitude is placed on.
+ *
+ * Returns: the average
+ */
+gdouble lon_avg(gdouble a, gdouble b)
+{
+	gdouble diff = ABS(a-b);
+	gdouble avg  = (a+b)/2;
+	if (diff > 180) {
+		if (avg >= 0)
+			avg -= 180;
+		else
+			avg += 180;
+	}
+	return avg;
+}