peirce_q: limit input to positive latitudes

Otherwise it returns junk (negative latitudes are mapped to
the same location as positive latitudes)

I'm a bit confused by PROJ peirce_q implementation. Looking at
the projection of the world, it looks like this matches the diamond
formulation of the right map shown at
https://desktop.arcgis.com/en/arcmap/latest/map/projections/peirce-quincuncial.htm,
but limited to the inner square of this diamond (which corresponds
to the northern hemisphere). We lack the 4 triangles on left, top,
right and bottom for the southern hemisphere. Furthermore, this
formulation of peirce_q does not seem to have the quincuncial
property of the square formulation (left images of the above ESRI
doc), or the one at https://en.wikipedia.org/wiki/Peirce_quincuncial_projection ...

1 files changed, 4 insertions, 0 deletions

diff --git a/src/projections/adams.cpp b/src/projections/adams.cpp
index 88fce8e5..e704c687 100644
--- a/src/projections/adams.cpp
+++ b/src/projections/adams.cpp
@@ -118,6 +118,10 @@ static PJ_XY adams_forward(PJ_LP lp, PJ *P) {
         }
         break;
     case PEIRCE_Q: {
+            if( lp.phi < -TOL ) {
+                proj_errno_set(P, PJD_ERR_TOLERANCE_CONDITION);
+                return proj_coord_error().xy;
+            }
             const double sl = sin(lp.lam);
             const double cl = cos(lp.lam);
             const double cp = cos(lp.phi);