New Transform type: Homography (OSGeo#11949)

Add new transform type, Homography.
Add functions to compute homography from a list of GCPs.
Add functions to serialize and deserialize a homography
Automatically select homography transfrom when there are 4 or 5 GCPs present.

Fixes OSGeo#11940

Author: NathanMOlson

alg/CMakeLists.txt

@@ -5,6 +5,7 @@ add_library(
   contour.cpp
   delaunay.c
   gdal_crs.cpp
+  gdal_homography.cpp
   gdal_octave.cpp
   gdal_rpc.cpp
   gdal_tps.cpp

alg/gdal_alg.h

@@ -165,6 +165,16 @@ int CPL_DLL GDALGCPTransform(void *pTransformArg, int bDstToSrc,
                              int nPointCount, double *x, double *y, double *z,
                              int *panSuccess);
 
+/* Homography transformer ... forward is to georef coordinates */
+void CPL_DLL *GDALCreateHomographyTransformer(double adfHomography[9]);
+void CPL_DLL *
+GDALCreateHomographyTransformerFromGCPs(int nGCPCount,
+                                        const GDAL_GCP *pasGCPList);
+void CPL_DLL GDALDestroyHomographyTransformer(void *pTransformArg);
+int CPL_DLL GDALHomographyTransform(void *pTransformArg, int bDstToSrc,
+                                    int nPointCount, double *x, double *y,
+                                    double *z, int *panSuccess);
+
 /* Thin Plate Spine transformer ... forward is to georef coordinates */
 
 void CPL_DLL *GDALCreateTPSTransformer(int nGCPCount,