Fix healpix 'auto' tiling (#191)

'auto' nside_tile is capped to nside
Add check that nside_tile <= nside in C++

python/proj/wcs.py

@@ -766,15 +766,15 @@ def compute_nside_tile(self, assembly, nActivePerThread=5, nThreads=None):
         """
         if self.nside_tile == 'auto':
             ## Estimate fsky
-            nside_tile0 = 4  # ntile = 192, for estimating fsky
+            nside_tile0 = min(4, self.nside)  # ntile = 192, for estimating fsky
             self.nside_tile = nside_tile0
             nActive = len(self.get_active_tiles(assembly)['active_tiles'])
             fsky = nActive / (12 * nside_tile0**2)
             if nThreads is None:
                 nThreads = so3g.useful_info()['omp_num_threads']
             # nside_tile is smallest power of 2 satisfying nTile >= nActivePerThread * nthread / fsky
             self.nside_tile = int(2**np.ceil(0.5 * np.log2(nActivePerThread * nThreads / (12 * fsky))))
-            # print('Setting nside_tile =', self.nside_tile)
+            self.nside_tile = min(self.nside_tile, self.nside)
         return self.nside_tile
 
     def get_active_tiles(self, assembly, assign=False):

src/Projection.cxx

@@ -596,6 +596,11 @@ class Pixelizor_Healpix<Tiled> {
         npix_per_tile = npix / ntiles;
         check_nside(nside); // check validity
         check_nside(nside_tile);
+        if (nside_tile > nside) {
+            std::ostringstream err;
+            err << "Invalid nside_tile " << nside_tile << " > nside " << nside;
+            throw ValueError_exception(err.str());
+        }
     }
   ~Pixelizor_Healpix() {};