Quick PR to fix GCOV block artifacts due to insufficient DEM margin (#857)

* fix DEM loading margin

* change DEM loading margin default from 50 pixels to 100 pixels

* use default DEM loading margin

Author: gshiroma

cxx/isce3/geocode/GeocodeCov.cpp

@@ -2109,11 +2109,9 @@ void Geocode<T>::_runBlock(
         getDemCoords = isce3::geometry::getDemCoordsDiffEpsg;
     }
 
-    // Load DEM using the block geogrid with a margin of 100 pixels
-    const double margin_x = std::abs(_geoGridSpacingX) * 100;
-    const double margin_y = std::abs(_geoGridSpacingY) * 100;
+    // Load DEM using the block geogrid extents
     auto error_code = loadDemFromProj(dem_raster, minX, maxX, minY, maxY,
-            &dem_interp_block, proj, margin_x, margin_y);
+            &dem_interp_block, proj);
 
     if (error_code != isce3::error::ErrorCode::Success) {
         _saveOptionalFiles(block_x, block_size_x, block_y, block_size_y,

cxx/isce3/geometry/RTC.cpp

@@ -1265,11 +1265,8 @@ void _RunBlock(const int jmax, const int block_size,
         getDemCoords = getDemCoordsDiffEpsg;
     }
 
-    const int dem_margin_in_pixels = 100;
-
     auto error_code = loadDemFromProj(dem_raster, minX, maxX, minY, maxY,
-            &dem_interp_block, proj, dem_margin_in_pixels,
-            dem_margin_in_pixels);
+            &dem_interp_block, proj);
 
     if (error_code != isce3::error::ErrorCode::Success) {
         return;

cxx/isce3/geometry/RTC.h

@@ -355,8 +355,8 @@ isce3::error::ErrorCode loadDemFromProj(isce3::io::Raster& dem_raster,
         const double minX, const double maxX, const double minY,
         const double maxY, DEMInterpolator* dem_interp_block,
         isce3::core::ProjectionBase* proj = nullptr,
-        const int dem_margin_x_in_pixels = 50,
-        const int dem_margin_y_in_pixels = 50);
+        const int dem_margin_x_in_pixels = 100,
+        const int dem_margin_y_in_pixels = 100);
 
 void areaProjIntegrateSegment(double y1, double y2, double x1, double x2,
                               int length, int width,