From 80792c8602966314e7da983ea20a245fd2a2ed4c Mon Sep 17 00:00:00 2001
From: Anna Petrasova <kratochanna@gmail.com>
Date: Fri, 12 May 2023 12:46:59 -0400
Subject: [PATCH] r.horizon: revert back to positive values only (#2955)

Enabling negative angles in r.horizon requires more work, the current simple implementation has problems (e.g. flat areas). Also r.sun doesn't work well with negative horizon values. See #2935 for discussion. For now, reverting back to horizon values >= 0 seems best. Note was added to manual page.
---
 raster/r.horizon/main.c                      |  2 +-
 raster/r.horizon/r.horizon.html              |  7 ++++---
 raster/r.horizon/testsuite/test_r_horizon.py | 18 ++++++++++++------
 3 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/raster/r.horizon/main.c b/raster/r.horizon/main.c
index 34ea26c5f3f..39d7db7b0b0 100644
--- a/raster/r.horizon/main.c
+++ b/raster/r.horizon/main.c
@@ -773,7 +773,7 @@ double horizon_height(void)
 {
     double height;
 
-    tanh0 = -1.0 / 0.0;  /* -inf */
+    tanh0 = 0.;
     length = 0;
 
     height = searching();
diff --git a/raster/r.horizon/r.horizon.html b/raster/r.horizon/r.horizon.html
index fd422dd2bd3..a67ed2aa949 100644
--- a/raster/r.horizon/r.horizon.html
+++ b/raster/r.horizon/r.horizon.html
@@ -134,9 +134,10 @@ <h2>METHOD</h2>
 
 <p>
 The output with the <b>-d</b> flag is azimuth degree (-90 to 90, where
-0 is parallel with the focal cell). In case of negative horizon values
-obtained this indicates that the horizon height is below the cell it is
-computed from.
+0 is parallel with the focal cell).
+
+<p> All horizon values are positive (or zero). While negative values are
+in theory possible, <b>r.horizon</b> currently does not support them.
 
 <h2>EXAMPLES</h2>
 
diff --git a/raster/r.horizon/testsuite/test_r_horizon.py b/raster/r.horizon/testsuite/test_r_horizon.py
index 4a8376c4f8f..72a7868c98d 100644
--- a/raster/r.horizon/testsuite/test_r_horizon.py
+++ b/raster/r.horizon/testsuite/test_r_horizon.py
@@ -30,7 +30,7 @@
 280.000000,0.039774
 300.000000,0.032360
 320.000000,0.014804
-340.000000,-0.001438
+340.000000,0.000000
 360.000000,0.004724
 20.000000,0.012612
 40.000000,0.015207
@@ -51,7 +51,7 @@
 280.000000,0.039774
 300.000000,0.032360
 320.000000,0.014804
-340.000000,-0.001438
+340.000000,0.000000
 360.000000,0.004724
 20.000000,0.012612
 40.000000,0.015207
@@ -120,9 +120,9 @@ def test_raster_mode_one_direction(self):
         )
         self.assertModule(module)
         ref = {
-            "min": -1.57079637050629,
+            "min": 0,
             "max": 0.70678365230560,
-            "stddev": 0.0708080140468585,
+            "stddev": 0.0360724286360789,
         }
         self.assertRasterFitsUnivar(
             raster="test_horizon_output_from_elevation_050",
@@ -146,7 +146,10 @@ def test_raster_mode_multiple_direction(self):
         self.runModule(module_list)
         stdout = module_list.outputs.stdout.strip()
         self.assertMultiLineEqual(
-            first="test_horizon_output_from_elevation_010_000\ntest_horizon_output_from_elevation_025_512",
+            first=(
+                "test_horizon_output_from_elevation_010_000\n"
+                "test_horizon_output_from_elevation_025_512"
+            ),
             second=stdout,
         )
 
@@ -167,7 +170,10 @@ def test_raster_mode_multiple_direction_offset(self):
         self.runModule(module_list)
         stdout = module_list.outputs.stdout.strip()
         self.assertMultiLineEqual(
-            first="test_horizon_output_from_elevation_090_000\ntest_horizon_output_from_elevation_105_512",
+            first=(
+                "test_horizon_output_from_elevation_090_000\n"
+                "test_horizon_output_from_elevation_105_512"
+            ),
             second=stdout,
         )