BUG: Mantis-942: fix detection of an identity geotransform

Code/IO/otbImageFileReader.txx

@@ -478,12 +478,21 @@ ImageFileReader<TOutputImage, ConvertPixelTraits>
     std::string projRef;
     itk::ExposeMetaData(dict, MetaDataKey::ProjectionRefKey, projRef);
 
+    // Compute spacing for an identity geotransform at current resolution
+    unsigned int resolution;
+    itk::ExposeMetaData<unsigned int>(dict,
+                                      MetaDataKey::ResolutionFactor,
+                                      resolution);
+    double idSpacing = 1.0;
+    if (resolution != 0)
+      idSpacing = 1.0 * vcl_pow((double)2.0, (double)resolution);
+
     const double Epsilon = 1.0E-12;
     if ( projRef.empty()
-         && vcl_abs(origin[0] - 0.5) > Epsilon
-         && vcl_abs(origin[1] - 0.5) > Epsilon
-         && vcl_abs(spacing[0] - 1) > Epsilon
-         && vcl_abs(spacing[1] - 1) > Epsilon)
+         && vcl_abs(origin[0] - 0.5 * spacing[0]) > Epsilon
+         && vcl_abs(origin[1] - 0.5 * spacing[1]) > Epsilon
+         && vcl_abs(spacing[0] - idSpacing) > Epsilon
+         && vcl_abs(spacing[1] - idSpacing) > Epsilon)
       {
       std::string wgs84ProjRef =
               "GEOGCS[\"GCS_WGS_1984\", DATUM[\"D_WGS_1984\", SPHEROID[\"WGS_1984\", 6378137, 298.257223563]],"