Initial commit

ocbrdf/brdf_utils.py

@@ -0,0 +1,46 @@
+import numpy as np
+import xarray as xr
+import os
+
+# Define default auxiliary data file (OLCI OCP ADF)
+ref_path = os.path.dirname(os.path.realpath(__file__))
+# ADF_OCP = os.path.join(ref_path, '..', 'AuxiliaryData/OCP/S3A_OL_2_OCP_AX_20160216T000000_20991231T235959_20240327T100000___________________EUM_O_AL_008.SEN3/OL_2_OCP_AX.nc')
+ADF_OCP = os.path.join(ref_path, 'BRDF_LUTs','BRDF_%s.nc')
+
+def solve_2nd_order_poly(A, B, C):
+    """ Solve 2nd order polynomial inversion 
+    where coefficients are xr dataArray
+    Take only positive solution, otherwise provide 0.
+    """
+
+    # Compute solution according to sign of delta
+    delta = B*B - 4*A*C
+    mask = delta > 0
+    
+    # By default (and when delta < 0), take value at extremum
+    x = - B / (2*A)
+    
+    # When delta > 0, take biggest solutions
+    x_1 = (-B.where(mask) - np.sqrt(delta.where(mask))) / (2*A.where(mask))
+    x_2 = (-B.where(mask) + np.sqrt(delta.where(mask))) / (2*A.where(mask))
+    x_sol = xr.where(x_1 > x_2, x_1, x_2)
+    x = xr.where(delta > 0, x_sol, x)
+    
+    # Take only positive value
+    x = xr.where(x > 0, x, 0.)
+
+    return x
+
+def drop_unused_coords(var):
+    for coord in var.coords:
+        if coord not in var.dims:
+            var = var.drop(coord)
+    return var
+
+def squeeze_trivial_dims(ds,dimOrderAccordingTo='Rw'):
+    squeezedDims = {}
+    for d0,dim in enumerate(ds[dimOrderAccordingTo].dims):
+        if ds.sizes[dim] == 1:
+            squeezedDims[dim] = d0
+
+    return ds.squeeze(), squeezedDims