Raise useful error message when trying to compute statistics and all tie...

Raise useful error message when trying to compute statistics and all tie points are flagged as false-positives.
Signed-off-by: Daniel Scheffler <danschef@gfz-potsdam.de>

arosics/Tie_Point_Grid.py

@@ -467,6 +467,9 @@ class Tie_Point_Grid(object):
         tbl = self.CoRegPoints_table
         tbl = tbl if include_outliers else tbl[tbl['OUTLIER'] == 0].copy() if 'OUTLIER' in tbl.columns else tbl
 
+        if not include_outliers and tbl.empty:
+            raise RuntimeError('Cannot compute the RMSE because all tie points are flagged as false-positives.')
+
         shifts = np.array(tbl['ABS_SHIFT'])
         shifts_sq = [i * i for i in shifts if i != self.outFillVal]
 
@@ -487,6 +490,9 @@ class Tie_Point_Grid(object):
         tbl = self.CoRegPoints_table
         tbl = tbl if include_outliers else tbl[tbl['OUTLIER'] == 0].copy()
 
+        if not include_outliers and tbl.empty:
+            raise RuntimeError('Cannot compute the overall SSIM because all tie points are flagged as false-positives.')
+
         ssim_col = np.array(tbl['SSIM_AFTER' if after_correction else 'SSIM_BEFORE'])
         ssim_col = [i * i for i in ssim_col if i != self.outFillVal]
 
@@ -577,6 +583,10 @@ class Tie_Point_Grid(object):
         tbl = tbl if include_outliers else tbl[tbl['OUTLIER'] == 0].copy() if 'OUTLIER' in tbl.columns else tbl
         tbl = tbl.copy().replace(self.outFillVal, np.nan)
 
+        if not include_outliers and tbl.empty:
+            raise RuntimeError('Cannot compute overall statistics '
+                               'because all tie points are flagged as false-positives.')
+
         def RMSE(shifts):
             shifts_sq = shifts ** 2
             return np.sqrt(sum(shifts_sq) / len(shifts_sq))