DOC: Refresh Development/Quickstart and remove Development/Threads (#2863)

* DOC: Refresh Development/Quickstart and remove Development/Threads

The document Development/Threads was severely out of date, and was
focussed on contrasting the current API with an old API that was
deprecated several years ago, and removed from the current PROJ earlier
this year.

Update Development/Quickstart to give more information about the use of
threading context, as a replacement for the content that was previously
in Threads.

Also give the example code examples/pj_obs_api_mini_demo.c a cleanup
pass to make it at least internally consistent with its own code style.

The header comments of the example code are still, much like the Threads
document, fixated on comparing proj.h against proj_api.h, which is an
interesting historical curio to be sure, but probably doesn't need to
persist here.  It might be worth cleaning this up further as a separate
exercise.

Fixes #2451

1 files changed, 17 insertions, 16 deletions

diff --git a/examples/pj_obs_api_mini_demo.c b/examples/pj_obs_api_mini_demo.c
index 3df94e2d..5cd5efe4 100644
--- a/examples/pj_obs_api_mini_demo.c
+++ b/examples/pj_obs_api_mini_demo.c
@@ -1,6 +1,6 @@
 /*******************************************************************************
-    Tiny test of an evolving new API, demonstrating simple examples of
-    2D and 3D transformations.
+    Simple example code demonstrating use of the proj.h API for 2D coordinate
+    transformations.
 
     The main transformation setup object is PJ, well known from the two
     former proj APIs (projects.h and proj_api.h)
@@ -42,7 +42,7 @@
 int main (void) {
     PJ_CONTEXT *C;
     PJ *P;
-    PJ* P_for_GIS;
+    PJ *norm;
     PJ_COORD a, b;
 
     /* or you may set C=PJ_DEFAULT_CTX if you are sure you will     */
@@ -54,35 +54,36 @@ int main (void) {
                                 "+proj=utm +zone=32 +datum=WGS84", /* or EPSG:32632 */
                                 NULL);
 
-    if (0==P) {
-        fprintf(stderr, "Oops\n");
+    if (0 == P) {
+        fprintf(stderr, "Failed to create transformation object.\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");
+    norm = proj_normalize_for_visualization(C, P);
+    if (0 == norm) {
+        fprintf(stderr, "Failed to normalize transformation object.\n");
         return 1;
     }
     proj_destroy(P);
-    P = P_for_GIS;
+    P = norm;
 
     /* a coordinate union representing Copenhagen: 55d N, 12d E    */
     /* 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);
+    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: %.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);
+    b = proj_trans(P, PJ_FWD, a);
+    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);
 
     /* Clean up */
-    proj_destroy (P);
-    proj_context_destroy (C); /* may be omitted in the single threaded case */
+    proj_destroy(P);
+    proj_context_destroy(C); /* may be omitted in the single threaded case */
     return 0;
 }