Invalidate sample layer past critical beta

xy points on the detector past the critical beta have very high values
and start appearing unrealistic. Just set any values to nan that are past
the critical beta.

Note that we are not invalidating map values past the critical beta for
now, because they actually appear okay when warping the polar view. This
is because they move too far and disappear (which is actually what we
want when warping to the polar view).

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

hexrd/xrdutil/phutil.py

@@ -21,11 +21,12 @@
 class SampleLayerDistortion:
     def __init__(self, panel,
                  layer_standoff, layer_thickness,
-                 pinhole_thickness):
+                 pinhole_thickness, pinhole_radius):
         self._panel = panel
         self._layer_standoff = layer_standoff
         self._layer_thickness = layer_thickness
         self._pinhole_thickness = pinhole_thickness
+        self._pinhole_radius = pinhole_radius
 
     @property
     def panel(self):
@@ -60,12 +61,21 @@ def pinhole_thickness(self):
     def pinhole_thickness(self, x):
         self._pinhole_thickness = float(x)
 
+    @property
+    def pinhole_radius(self):
+        return self._pinhole_radius
+
+    @pinhole_radius.setter
+    def pinhole_radius(self, x):
+        self._pinhole_radius = float(x)
+
     def apply(self, xy_pts, return_nominal=True):
         """
         """
         return tth_corr_sample_layer(self.panel, xy_pts,
                                      self.layer_standoff, self.layer_thickness,
                                      self.pinhole_thickness,
+                                     self.pinhole_radius,
                                      return_nominal=return_nominal)
 
 
@@ -133,7 +143,8 @@ def apply(self, xy_pts, return_nominal=True):
 
 def tth_corr_sample_layer(panel, xy_pts,
                           layer_standoff, layer_thickness,
-                          pinhole_thickness, return_nominal=True):
+                          pinhole_thickness, pinhole_radius,
+                          return_nominal=True):
     """
     Compute the Bragg angle distortion associated with a specific sample
     layer in a pinhole camera.
@@ -152,13 +163,18 @@ def tth_corr_sample_layer(panel, xy_pts,
         The thickness of the sample layer in mm.
     pinhole_thickness : scalar
         The thickenss (height) of the pinhole (cylinder) in mm
+    pinhole_radius : scalar
+        The radius of the pinhole in mm.
 
     Returns
     -------
     TYPE
         DESCRIPTION.
 
     """
+    # Compute the critical beta angle. Anything past this is invalid.
+    critical_beta = np.arctan(2 * pinhole_radius / pinhole_thickness)
+
     source_distance = panel.xrs_dist
 
     xy_pts = np.atleast_2d(xy_pts)
@@ -173,6 +189,8 @@ def tth_corr_sample_layer(panel, xy_pts,
 
     dhats = xfcapi.unitRowVector(panel.cart_to_dvecs(xy_pts))
     cos_beta = -dhats[:, 2]
+    # Invalidate values past the critical beta
+    cos_beta[np.arccos(cos_beta) > critical_beta] = np.nan
     cos_tthn = np.cos(ref_tth)
     sin_tthn = np.sin(ref_tth)
     tth_corr = np.arctan(sin_tthn/(source_distance*cos_beta/zs - cos_tthn))
@@ -185,7 +203,7 @@ def tth_corr_sample_layer(panel, xy_pts,
 
 def tth_corr_map_sample_layer(instrument,
                               layer_standoff, layer_thickness,
-                              pinhole_thickness):
+                              pinhole_thickness, pinhole_radius):
     """
     Compute the Bragg angle distortion fields for an instrument associated
     with a specific sample layer in a pinhole camera.
@@ -201,6 +219,8 @@ def tth_corr_map_sample_layer(instrument,
         The thickness of the sample layer in mm.
     pinhole_thickness : scalar
         The thickenss (height) of the pinhole (cylinder) in mm
+    pinhole_radius : scalar
+        The radius of the pinhole in mm.
 
     Returns
     -------
@@ -215,6 +235,11 @@ def tth_corr_map_sample_layer(instrument,
                       attribute of the same name.
 
     """
+    # We currently don't invalidate tth values after the critical beta for
+    # this map, because it actually looks okay for warping to the polar
+    # view. But that is something we could do in the future:
+    # critical_beta = np.arctan(2 * pinhole_radius / pinhole_thickness)
+
     zs = layer_standoff + 0.5*layer_thickness + 0.5*pinhole_thickness
     tth_corr = dict.fromkeys(instrument.detectors)
     for det_key, panel in instrument.detectors.items():
@@ -223,6 +248,8 @@ def tth_corr_map_sample_layer(instrument,
         xy_data = np.vstack((px.flatten(), py.flatten())).T
         dhats = xfcapi.unitRowVector(panel.cart_to_dvecs(xy_data))
         cos_beta = -dhats[:, 2]
+        # Invalidate values past the critical beta
+        # cos_beta[np.arccos(cos_beta) > critical_beta] = np.nan
         cos_tthn = np.cos(ref_ptth.flatten())
         sin_tthn = np.sin(ref_ptth.flatten())
         tth_corr[det_key] = np.arctan(
@@ -247,7 +274,7 @@ def tth_corr_pinhole(panel, xy_pts,
     pinhole_thickness : scalar
         The thickenss (height) of the pinhole (cylinder) in mm
     pinhole_radius : scalar
-        The radius ofhte pinhole in mm.
+        The radius of the pinhole in mm.
 
     Returns
     -------