Add sign for elevation calculation following the used convension to i…

…nterferogram pairs order and baseline sign

pygmtsar/pygmtsar/Stack_incidence.py

@@ -430,14 +430,15 @@ def elevation_m(self, unwrap, baseline):
         import numpy as np
 
         assert self.is_ra(unwrap), 'ERROR: unwrapped phase needs to be defined in radar coordinates'
-    
+
         # expected accuracy about 0.01%
         #wavelength, slant_range = self.PRM().get('radar_wavelength','SC_height')
         wavelength, slant_range_start,slant_range_end = self.PRM().get('radar_wavelength', 'SC_height_start', 'SC_height_end')
         slant_range = xr.DataArray(np.linspace(slant_range_start,slant_range_end, unwrap.shape[1]),
                                    coords=[unwrap.coords['x']])
         incidence = self.incidence_angle().reindex_like(unwrap, method='nearest')
-        return (wavelength*unwrap*slant_range*np.cos(incidence)/(4*np.pi*baseline)).rename('ele')
+        # sign corresponding to baseline and phase signs
+        return -(wavelength*unwrap*slant_range*np.cos(incidence)/(4*np.pi*baseline)).rename('ele')
 
     def compute_satellite_look_vector(self, interactive=False):
         #import dask