Merge pull request #11700 from rouault/fix_GeodesicLength

Fix GeodesicLength() that was quite severely broken as working only on closed linestrings (3.10.0 regression)
OSGeo · Jan 22, 2025 · 00bc255 · 00bc255
2 parents 3984098 + aa5fde1
commit 00bc255
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Showing 2 changed files with 49 additions and 15 deletions.
diff --git a/autotest/ogr/ogr_geom.py b/autotest/ogr/ogr_geom.py
@@ -4559,12 +4559,34 @@ def test_ogr_geom_GeodesicArea():
 @gdaltest.enable_exceptions()
 def test_ogr_geom_GeodesicLength():
 
+    # Lat, lon order, not forming a polygon
+    g = ogr.CreateGeometryFromWkt("LINESTRING(49 2,49 3)")
+    srs = osr.SpatialReference()
+    srs.ImportFromEPSG(4326)
+    g.AssignSpatialReference(srs)
+    l1 = g.GeodesicLength()
+    assert l1 == pytest.approx(73171.26435678436)
+
+    g = ogr.CreateGeometryFromWkt("LINESTRING(49 3,48 3)")
+    srs = osr.SpatialReference()
+    srs.ImportFromEPSG(4326)
+    g.AssignSpatialReference(srs)
+    l2 = g.GeodesicLength()
+    assert l2 == pytest.approx(111200.0367623785)
+
+    g = ogr.CreateGeometryFromWkt("LINESTRING(48 3,49 2)")
+    srs = osr.SpatialReference()
+    srs.ImportFromEPSG(4326)
+    g.AssignSpatialReference(srs)
+    l3 = g.GeodesicLength()
+    assert l3 == pytest.approx(133514.4852804854)
+
     # Lat, lon order
     g = ogr.CreateGeometryFromWkt("LINESTRING(49 2,49 3,48 3,49 2)")
     srs = osr.SpatialReference()
     srs.ImportFromEPSG(4326)
     g.AssignSpatialReference(srs)
-    assert g.GeodesicLength() == pytest.approx(317885.78639964823)
+    assert g.GeodesicLength() == pytest.approx(l1 + l2 + l3)
 
     # Lat, lon order
     g = ogr.CreateGeometryFromWkt("POLYGON((49 2,49 3,48 3,49 2))")

diff --git a/ogr/ogrlinestring.cpp b/ogr/ogrlinestring.cpp
@@ -3124,12 +3124,14 @@ double OGRLineString::get_Area() const
 }
 
 /************************************************************************/
-/*                        GetGeodesicAreaOrLength()                     */
+/*                           GetGeodesicInputs()                        */
 /************************************************************************/
 
-static bool GetGeodesicAreaOrLength(const OGRLineString *poLS,
-                                    const OGRSpatialReference *poSRSOverride,
-                                    double *pdfArea, double *pdfLength)
+static bool GetGeodesicInputs(const OGRLineString *poLS,
+                              const OGRSpatialReference *poSRSOverride,
+                              const char *pszComputationType, geod_geodesic &g,
+                              std::vector<double> &adfLat,
+                              std::vector<double> &adfLon)
 {
     if (!poSRSOverride)
         poSRSOverride = poLS->getSpatialReference();
@@ -3138,7 +3140,7 @@ static bool GetGeodesicAreaOrLength(const OGRLineString *poLS,
     {
         CPLError(CE_Failure, CPLE_AppDefined,
                  "Cannot compute %s on ellipsoid due to missing SRS",
-                 pdfArea ? "area" : "length");
+                 pszComputationType);
         return false;
     }
 
@@ -3150,12 +3152,9 @@ static bool GetGeodesicAreaOrLength(const OGRLineString *poLS,
     if (eErr != OGRERR_NONE)
         return false;
 
-    geod_geodesic g;
     geod_init(&g, dfSemiMajor,
               dfInvFlattening != 0 ? 1.0 / dfInvFlattening : 0.0);
 
-    std::vector<double> adfLat;
-    std::vector<double> adfLon;
     const int nPointCount = poLS->getNumPoints();
     adfLat.reserve(nPointCount);
     adfLon.reserve(nPointCount);
@@ -3208,8 +3207,6 @@ static bool GetGeodesicAreaOrLength(const OGRLineString *poLS,
         adfLat[i] *= dfToDegrees;
     }
 
-    geod_polygonarea(&g, adfLat.data(), adfLon.data(),
-                     static_cast<int>(adfLat.size()), pdfArea, pdfLength);
     return true;
 }
 
@@ -3220,9 +3217,14 @@ static bool GetGeodesicAreaOrLength(const OGRLineString *poLS,
 double
 OGRLineString::get_GeodesicArea(const OGRSpatialReference *poSRSOverride) const
 {
-    double dfArea = 0;
-    if (!GetGeodesicAreaOrLength(this, poSRSOverride, &dfArea, nullptr))
+    geod_geodesic g;
+    std::vector<double> adfLat;
+    std::vector<double> adfLon;
+    if (!GetGeodesicInputs(this, poSRSOverride, "area", g, adfLat, adfLon))
         return -1.0;
+    double dfArea = -1.0;
+    geod_polygonarea(&g, adfLat.data(), adfLon.data(),
+                     static_cast<int>(adfLat.size()), &dfArea, nullptr);
     return std::fabs(dfArea);
 }
 
@@ -3233,9 +3235,19 @@ OGRLineString::get_GeodesicArea(const OGRSpatialReference *poSRSOverride) const
 double OGRLineString::get_GeodesicLength(
     const OGRSpatialReference *poSRSOverride) const
 {
+    geod_geodesic g;
+    std::vector<double> adfLat;
+    std::vector<double> adfLon;
+    if (!GetGeodesicInputs(this, poSRSOverride, "length", g, adfLat, adfLon))
+        return -1.0;
     double dfLength = 0;
-    if (!GetGeodesicAreaOrLength(this, poSRSOverride, nullptr, &dfLength))
-        return -1;
+    for (size_t i = 0; i + 1 < adfLon.size(); ++i)
+    {
+        double dfSegmentLength = 0;
+        geod_inverse(&g, adfLat[i], adfLon[i], adfLat[i + 1], adfLon[i + 1],
+                     &dfSegmentLength, nullptr, nullptr);
+        dfLength += dfSegmentLength;
+    }
     return dfLength;
 }