Merge pull request #841 from HEXRD/positive-areas

Ensure areas are positive in auto powder picking

Author: psavery

hexrd/gridutil.py

@@ -147,6 +147,10 @@ def cellCentroids(crd, con):
 
 @numba.njit(nogil=True, cache=True)
 def compute_areas(xy_eval_vtx, conn):
+    # NOTE: this function may return negative areas if the vertices
+    # are passed in the opposite order to the function. This happens
+    # if the beam vector is in the opposite direction (positive Z
+    # instead of the usual negative Z)
     areas = np.empty(len(conn))
     for i in range(len(conn)):
         vtx0x, vtx0y = xy_eval_vtx[conn[i, 0]]

hexrd/instrument/hedm_instrument.py

@@ -2686,6 +2686,12 @@ def _extract_ring_line_positions(iter_args, instr_cfg, panel, eta_tol, npdiv,
         # strip relevant objects out of current patch
         vtx_angs, vtx_xys, conn, areas, xys_eval, ijs = patch
 
+        # These areas can be negative if the beam vector is in
+        # the opposite direction than it normally is in (positive
+        # Z instead of the usual negative Z). Take the absolute
+        # value of the areas to ensure they are positive.
+        areas = np.abs(areas)
+
         # need to reshape eval pts for interpolation
         xy_eval = np.vstack([
             xys_eval[0].flatten(),