[Backport 6.0] Doc: update quickstart with PROJ 6 API + add PROJ 4->6 migration guide (fixes #1403) (#1450)6.0

[Backport 6.0] Doc: update quickstart with PROJ 6 API + add PROJ 4->6 migration guide (fixes #1403)

1 files changed, 25 insertions, 6 deletions

diff --git a/examples/pj_obs_api_mini_demo.c b/examples/pj_obs_api_mini_demo.c
index 94520490..3df94e2d 100644
--- a/examples/pj_obs_api_mini_demo.c
+++ b/examples/pj_obs_api_mini_demo.c
@@ -42,23 +42,42 @@
 int main (void) {
     PJ_CONTEXT *C;
     PJ *P;
+    PJ* P_for_GIS;
     PJ_COORD a, b;
 
     /* or you may set C=PJ_DEFAULT_CTX if you are sure you will     */
     /* use PJ objects from only one thread                          */
     C = proj_context_create();
 
-    P = proj_create (C, "+proj=utm +zone=32 +ellps=GRS80");
-    if (0==P)
-        return puts ("Oops"), 0;
+    P = proj_create_crs_to_crs (C,
+                                "EPSG:4326",
+                                "+proj=utm +zone=32 +datum=WGS84", /* or EPSG:32632 */
+                                NULL);
+
+    if (0==P) {
+        fprintf(stderr, "Oops\n");
+        return 1;
+    }
+
+    /* This will ensure that the order of coordinates for the input CRS */
+    /* will be longitude, latitude, whereas EPSG:4326 mandates latitude, */
+    /* longitude */
+    P_for_GIS = proj_normalize_for_visualization(C, P);
+    if( 0 == P_for_GIS )  {
+        fprintf(stderr, "Oops\n");
+        return 1;
+    }
+    proj_destroy(P);
+    P = P_for_GIS;
 
     /* a coordinate union representing Copenhagen: 55d N, 12d E    */
-    /* note: PROJ.4 works in radians, hence the proj_torad() calls */
-    a = proj_coord (proj_torad(12), proj_torad(55), 0, 0);
+    /* Given that we have used proj_normalize_for_visualization(), the order of
+    /* coordinates is longitude, latitude, and values are expressed in degrees. */
+    a = proj_coord (12, 55, 0, 0);
 
     /* transform to UTM zone 32, then back to geographical */
     b = proj_trans (P, PJ_FWD, a);
-    printf ("easting: %g, northing: %g\n", b.enu.e, b.enu.n);
+    printf ("easting: %.3f, northing: %.3f\n", b.enu.e, b.enu.n);
     b = proj_trans (P, PJ_INV, b);
     printf ("longitude: %g, latitude: %g\n", b.lp.lam, b.lp.phi);