Remove duplicate Laue spots from simulator

This issue arose from #509, due to somewhat complex details.

In short, the old `gvecToDetectorXY()` would filter out g-vectors going
the wrong way (they would result in `nan`), but `gvecToDetectorXYArray()` would
not.

The new `gvec_to_xy()` has behavior matching `gvecToDetectorXYArray()`. But
that means that places where `gvecToDetectorXY()` used to be used, we need
to verify that the function does not receive g-vectors going the wrong way.

Looking through the code, however, I only found one place where
`gvecToDetectorXY()` used to receive g-vectors going the wrong way. It was
the Laue overlay simulator, which would compute g-vectors from symmetrical
HKLs (which is why it would have duplicate g-vectors going the wrong way).

All other cases where `gvecToDetectorXY()` was called would be after
the g-vectors were computed from `anglesToGvec()`, which I believe should
always produce g-vectors going in the correct direction.

As such, we only need to filter out wrong-direction g-vectors in the
Laue simulator.

Fixes: HEXRD/hexrdgui#1412

Signed-off-by: Patrick Avery <[email protected]>

hexrd/instrument/detector.py

@@ -1364,6 +1364,14 @@ def simulate_laue_pattern(self, crystal_data,
 
             # and the unit plane normals (G-vectors) in CRYSTAL FRAME
             gvec_c = np.dot(plane_data.latVecOps['B'], hkls)
+
+            # Filter out g-vectors going in the wrong direction. `gvec_to_xy()` used
+            # to do this, but not anymore.
+            bvec_z = self.bvec[2]
+            to_keep = gvec_c.T[:, 2] * bvec_z <= 0
+
+            hkls = hkls.T[to_keep].T
+            gvec_c = gvec_c.T[to_keep].T
         elif len(crystal_data) == 2:
             # !!! should clean this up
             hkls = np.array(crystal_data[0])