r.horizon: adjust bufferzone to multiples of resolution (#3384)

* r.horizon: adjust bufferzone to multiples of resolution

* fix test

* restrict input bufferzone to positive values

* add tests for negative bufferzone

raster/r.horizon/main.c

@@ -233,6 +233,7 @@ int main(int argc, char *argv[])
     parm.bufferzone->description =
         _("For horizon rasters, read from the DEM an extra buffer around the "
           "present region");
+    parm.bufferzone->options = "0-";
     parm.bufferzone->guisection = _("Raster mode");
 
     parm.e_buff = G_define_option();
@@ -241,6 +242,7 @@ int main(int argc, char *argv[])
     parm.e_buff->required = NO;
     parm.e_buff->description = _("For horizon rasters, read from the DEM an "
                                  "extra buffer eastward the present region");
+    parm.e_buff->options = "0-";
     parm.e_buff->guisection = _("Raster mode");
 
     parm.w_buff = G_define_option();
@@ -249,6 +251,7 @@ int main(int argc, char *argv[])
     parm.w_buff->required = NO;
     parm.w_buff->description = _("For horizon rasters, read from the DEM an "
                                  "extra buffer westward the present region");
+    parm.w_buff->options = "0-";
     parm.w_buff->guisection = _("Raster mode");
 
     parm.n_buff = G_define_option();
@@ -257,6 +260,7 @@ int main(int argc, char *argv[])
     parm.n_buff->required = NO;
     parm.n_buff->description = _("For horizon rasters, read from the DEM an "
                                  "extra buffer northward the present region");
+    parm.n_buff->options = "0-";
     parm.n_buff->guisection = _("Raster mode");
 
     parm.s_buff = G_define_option();
@@ -265,6 +269,7 @@ int main(int argc, char *argv[])
     parm.s_buff->required = NO;
     parm.s_buff->description = _("For horizon rasters, read from the DEM an "
                                  "extra buffer southward the present region");
+    parm.s_buff->options = "0-";
     parm.s_buff->guisection = _("Raster mode");
 
     parm.maxdistance = G_define_option();
@@ -499,6 +504,12 @@ int main(int argc, char *argv[])
         if (nbufferZone == 0.)
             nbufferZone = bufferZone;
 
+        /* adjust buffer to multiples of resolution */
+        ebufferZone = (int)(ebufferZone / stepx) * stepx;
+        wbufferZone = (int)(wbufferZone / stepx) * stepx;
+        sbufferZone = (int)(sbufferZone / stepy) * stepy;
+        nbufferZone = (int)(nbufferZone / stepy) * stepy;
+
         new_cellhd.rows += (int)((nbufferZone + sbufferZone) / stepy);
         new_cellhd.cols += (int)((ebufferZone + wbufferZone) / stepx);
 

raster/r.horizon/testsuite/test_r_horizon.py

@@ -222,6 +222,86 @@ def test_raster_mode_multiple_direction_offset(self):
             second=stdout,
         )
 
+    def test_raster_mode_bufferzone(self):
+        """Test buffer 100 m and 109 m with resolution 10 gives the same result"""
+        self.runModule(
+            "g.region",
+            raster="elevation",
+            n="n-5000",
+            s="s+5000",
+            e="e-5000",
+            w="w+5000",
+        )
+        # raises ValueError from pygrass parameter check
+        self.assertRaises(
+            ValueError,
+            SimpleModule,
+            "r.horizon",
+            elevation="elevation",
+            output=self.horizon_output,
+            direction=50,
+            bufferzone=-100,
+        )
+        self.assertRaises(
+            ValueError,
+            SimpleModule,
+            "r.horizon",
+            elevation="elevation",
+            output=self.horizon_output,
+            direction=50,
+            e_buff=100,
+            n_buff=0,
+            s_buff=-100,
+            w_buff=-100,
+        )
+        module = SimpleModule(
+            "r.horizon",
+            elevation="elevation",
+            output=self.horizon_output,
+            direction=50,
+            bufferzone=100,
+        )
+        self.assertModule(module)
+        ref = {
+            "mean": 0.0344791,
+        }
+        output = "test_horizon_output_from_elevation_050"
+        self.assertRasterFitsUnivar(
+            raster=output,
+            reference=ref,
+            precision=1e-6,
+        )
+        module = SimpleModule(
+            "r.horizon",
+            elevation="elevation",
+            output=self.horizon_output,
+            direction=50,
+            bufferzone=103,
+        )
+        self.assertModule(module)
+        self.assertRasterFitsUnivar(
+            raster=output,
+            reference=ref,
+            precision=1e-6,
+        )
+        module = SimpleModule(
+            "r.horizon",
+            elevation="elevation",
+            output=self.horizon_output,
+            direction=50,
+            bufferzone=95,
+        )
+        self.assertModule(module)
+        ref = {
+            "mean": 0.0344624,
+        }
+        self.assertRasterFitsUnivar(
+            raster=output,
+            reference=ref,
+            precision=1e-6,
+        )
+        self.runModule("g.region", raster="elevation")
+
 
 if __name__ == "__main__":
     test()