Merge pull request #4416 from rouault/viewshed_change_cc

gdal_viewshed: change default value of -cc (curvature coefficient) to 0.85714, standard value for atmospheric refraction (fixes #4415)

autotest/utilities/test_gdal_viewshed.py

@@ -60,7 +60,7 @@ def test_gdal_viewshed():
     ds = None
     gdal.Unlink(viewshed_in)
     gdal.Unlink(viewshed_out)
-    assert cs == 42397
+    assert cs == 14613
     assert nodata is None
 
 
@@ -77,7 +77,7 @@ def test_gdal_viewshed_alternative_modes():
     nodata = ds.GetRasterBand(1).GetNoDataValue()
     ds = None
     gdal.Unlink(viewshed_out)
-    assert cs == 48478
+    assert cs == 45734
     assert nodata is None
 
     _, err = gdaltest.runexternal_out_and_err(test_cli_utilities.get_gdal_viewshed_path() + ' -om GROUND -oz {} -ox {} -oy {} {} {}'.format(oz[0], ox[0], oy[0], viewshed_in, viewshed_out))
@@ -89,7 +89,7 @@ def test_gdal_viewshed_alternative_modes():
     ds = None
     gdal.Unlink(viewshed_in)
     gdal.Unlink(viewshed_out)
-    assert cs == 49633
+    assert cs == 8364
     assert nodata is None
 
 
@@ -98,7 +98,7 @@ def test_gdal_viewshed_alternative_modes():
 
 def test_gdal_viewshed_all_options():
     make_viewshed_input()
-    _, err = gdaltest.runexternal_out_and_err(test_cli_utilities.get_gdal_viewshed_path() + ' -om NORMAL -f GTiff -oz {} -ox {} -oy {} -b 1 -a_nodata 0 -tz 5 -md 20000 -cc 0.85714 -iv 127 -vv 254 -ov 0 {} {}'.format(oz[1], ox[0], oy[0], viewshed_in, viewshed_out))
+    _, err = gdaltest.runexternal_out_and_err(test_cli_utilities.get_gdal_viewshed_path() + ' -om NORMAL -f GTiff -oz {} -ox {} -oy {} -b 1 -a_nodata 0 -tz 5 -md 20000 -cc 0 -iv 127 -vv 254 -ov 0 {} {}'.format(oz[1], ox[0], oy[0], viewshed_in, viewshed_out))
     assert err is None or err == ''
     ds = gdal.Open(viewshed_out)
     assert ds
@@ -107,7 +107,7 @@ def test_gdal_viewshed_all_options():
     ds = None
     gdal.Unlink(viewshed_in)
     gdal.Unlink(viewshed_out)
-    assert cs == 24390
+    assert cs == 24435
     assert nodata == 0
 
 

gdal/apps/gdal_viewshed.cpp

@@ -90,7 +90,8 @@ MAIN_START(argc, argv)
     double dfInvisibleVal = 0.0;
     double dfOutOfRangeVal = 0.0;
     double dfNoDataVal = -1.0;
-    double dfCurvCoeff = 0.0;
+    // Value for standard atmospheric refraction. See doc/source/programs/gdal_viewshed.rst
+    double dfCurvCoeff = 0.85714;
     const char *pszDriverName = nullptr;
     const char *pszSrcFilename = nullptr;
     const char *pszDstFilename = nullptr;

gdal/doc/source/programs/gdal_viewshed.rst

@@ -45,7 +45,7 @@ Byte. With the -mode flag can also return a minimum visible height raster of typ
 .. option:: -b <band>
 
    Select an input band **band** containing the DEM data. Bands are numbered from 1.
-   Only a single band can be used. Only the part of the raster within the specified 
+   Only a single band can be used. Only the part of the raster within the specified
    maximum distance around the observer point is processed.
 
 .. option:: -a_nodata <value>
@@ -99,7 +99,7 @@ Byte. With the -mode flag can also return a minimum visible height raster of typ
      {SphereDiameterFactor}=1/{CurvCoeff}=1/(1-{RefractionCoeff})
 
    For visible light, the standard atmospheric refraction coefficient that is generally used is 1/7.
-   Thus the default value for CurvCoeff that gdal_viewshed uses is 0.85714 (=~ 1-1/7).
+   Thus the default value (since GDAL 3.4) for CurvCoeff that gdal_viewshed uses is 0.85714 (=~ 1-1/7).
 
    The height of the DEM is corrected according to the following formula: