Add elevation utils method to collect significant elevation values for a project

python/PyQt6/core/auto_generated/qgselevationutils.sip.in

@@ -28,6 +28,16 @@ Calculates the elevation range for a ``project``.
 
 This method considers the elevation (or z) range available from layers contained within the project and
 returns the maximal combined elevation range of these layers.
+%End
+
+    static QList< double > significantZValuesForProject( QgsProject *project );
+%Docstring
+Returns a list of significant elevation/z-values for the specified ``project``, using
+the values from layers contained by the project.
+
+These values will be highlighted in elevation related widgets for the project.
+
+.. versionadded:: 3.38
 %End
 
     static bool canEnableElevationForLayer( QgsMapLayer *layer );

python/core/auto_generated/qgselevationutils.sip.in

@@ -28,6 +28,16 @@ Calculates the elevation range for a ``project``.
 
 This method considers the elevation (or z) range available from layers contained within the project and
 returns the maximal combined elevation range of these layers.
+%End
+
+    static QList< double > significantZValuesForProject( QgsProject *project );
+%Docstring
+Returns a list of significant elevation/z-values for the specified ``project``, using
+the values from layers contained by the project.
+
+These values will be highlighted in elevation related widgets for the project.
+
+.. versionadded:: 3.38
 %End
 
     static bool canEnableElevationForLayer( QgsMapLayer *layer );

src/core/qgselevationutils.cpp

@@ -54,6 +54,31 @@ QgsDoubleRange QgsElevationUtils::calculateZRangeForProject( QgsProject *project
                          std::isnan( max ) ? std::numeric_limits< double >::max() : max );
 }
 
+QList<double> QgsElevationUtils::significantZValuesForProject( QgsProject *project )
+{
+  const QMap<QString, QgsMapLayer *> &mapLayers = project->mapLayers();
+  QSet< double > values;
+
+  QgsMapLayer *currentLayer = nullptr;
+  for ( QMap<QString, QgsMapLayer *>::const_iterator it = mapLayers.constBegin(); it != mapLayers.constEnd(); ++it )
+  {
+    currentLayer = it.value();
+
+    if ( !currentLayer->elevationProperties() || !currentLayer->elevationProperties()->hasElevation() )
+      continue;
+
+    const QList< double > layerValues = currentLayer->elevationProperties()->significantZValues( currentLayer );
+    for ( double value : layerValues )
+    {
+      values.insert( value );
+    }
+  }
+
+  QList< double > res = qgis::setToList( values );
+  std::sort( res.begin(), res.end() );
+  return res;
+}
+
 bool QgsElevationUtils::canEnableElevationForLayer( QgsMapLayer *layer )
 {
   return static_cast< bool >( layer->elevationProperties() );

src/core/qgselevationutils.h

@@ -41,6 +41,16 @@ class CORE_EXPORT QgsElevationUtils
      */
     static QgsDoubleRange calculateZRangeForProject( QgsProject *project );
 
+    /**
+     * Returns a list of significant elevation/z-values for the specified \a project, using
+     * the values from layers contained by the project.
+     *
+     * These values will be highlighted in elevation related widgets for the project.
+     *
+     * \since QGIS 3.38
+     */
+    static QList< double > significantZValuesForProject( QgsProject *project );
+
     /**
      * Returns TRUE if elevation can be enabled for a map \a layer.
      *

tests/src/python/CMakeLists.txt

@@ -64,6 +64,7 @@ ADD_PYTHON_TEST(PyQgsDatumTransform test_qgsdatumtransforms.py)
 ADD_PYTHON_TEST(PyQgsDelimitedTextProvider test_qgsdelimitedtextprovider.py)
 ADD_PYTHON_TEST(PyQgsDistanceArea test_qgsdistancearea.py)
 ADD_PYTHON_TEST(PyQgsElevationControllerWidget test_qgselevationcontrollerwidget.py)
+ADD_PYTHON_TEST(PyQgsElevationUtils test_qgselevationutils.py)
 ADD_PYTHON_TEST(PyQgsEllipsoidUtils test_qgsellipsoidutils.py)
 ADD_PYTHON_TEST(PyQgsEmbeddedSymbolRenderer test_qgsembeddedsymbolrenderer.py)
 ADD_PYTHON_TEST(PyQgsExifTools test_qgsexiftools.py)

tests/src/python/test_qgselevationutils.py

@@ -0,0 +1,117 @@
+"""QGIS Unit tests for QgsElevationUtils
+
+.. note:: This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+"""
+
+import os
+
+from qgis.core import (
+    Qgis,
+    QgsProject,
+    QgsRasterLayer,
+    QgsElevationUtils,
+    QgsDoubleRange
+)
+import unittest
+from qgis.testing import start_app, QgisTestCase
+
+from utilities import unitTestDataPath
+
+# Convenience instances in case you may need them
+# not used in this test
+start_app()
+TEST_DATA_DIR = unitTestDataPath()
+
+
+class TestQgsElevationUtils(QgisTestCase):
+
+    def test_z_range_for_project(self):
+        """
+        Test calculating z range for a project
+        """
+        project = QgsProject()
+        self.assertEqual(
+            QgsElevationUtils.calculateZRangeForProject(project),
+            QgsDoubleRange())
+
+        raster_layer = QgsRasterLayer(os.path.join(unitTestDataPath(), 'landsat_4326.tif'))
+        self.assertTrue(raster_layer.isValid())
+        project.addMapLayer(raster_layer)
+        self.assertEqual(
+            QgsElevationUtils.calculateZRangeForProject(project),
+            QgsDoubleRange())
+
+        props = raster_layer.elevationProperties()
+        props.setEnabled(True)
+        props.setMode(Qgis.RasterElevationMode.FixedRangePerBand)
+        props.setFixedRangePerBand({1: QgsDoubleRange(103.1, 106.8),
+                                   2: QgsDoubleRange(106.8, 116.8),
+                                   3: QgsDoubleRange(116.8, 126.8)})
+        self.assertEqual(
+            QgsElevationUtils.calculateZRangeForProject(project),
+            QgsDoubleRange(103.1, 126.8))
+
+        raster_layer2 = QgsRasterLayer(os.path.join(unitTestDataPath(), 'landsat_4326.tif'))
+        self.assertTrue(raster_layer2.isValid())
+        project.addMapLayer(raster_layer2)
+        self.assertEqual(
+            QgsElevationUtils.calculateZRangeForProject(project),
+            QgsDoubleRange(103.1, 126.8))
+
+        props = raster_layer2.elevationProperties()
+        props.setEnabled(True)
+        props.setMode(Qgis.RasterElevationMode.FixedRangePerBand)
+        props.setFixedRangePerBand({1: QgsDoubleRange(103.1, 106.8),
+                                   2: QgsDoubleRange(106.8, 116.8),
+                                   3: QgsDoubleRange(126.8, 136.8)})
+        self.assertEqual(
+            QgsElevationUtils.calculateZRangeForProject(project),
+            QgsDoubleRange(103.1, 136.8))
+
+    def test_significant_z_values_for_project(self):
+        """
+        Test calculating significant z values for a project
+        """
+        project = QgsProject()
+        self.assertFalse(
+            QgsElevationUtils.significantZValuesForProject(project))
+
+        raster_layer = QgsRasterLayer(os.path.join(unitTestDataPath(), 'landsat_4326.tif'))
+        self.assertTrue(raster_layer.isValid())
+        project.addMapLayer(raster_layer)
+        self.assertFalse(
+            QgsElevationUtils.significantZValuesForProject(project))
+
+        props = raster_layer.elevationProperties()
+        props.setEnabled(True)
+        props.setMode(Qgis.RasterElevationMode.FixedRangePerBand)
+        props.setFixedRangePerBand({1: QgsDoubleRange(103.1, 106.8),
+                                   2: QgsDoubleRange(106.8, 116.8),
+                                   3: QgsDoubleRange(116.8, 126.8)})
+        self.assertEqual(
+            QgsElevationUtils.significantZValuesForProject(project),
+            [103.1, 106.8, 116.8, 126.8])
+
+        raster_layer2 = QgsRasterLayer(os.path.join(unitTestDataPath(), 'landsat_4326.tif'))
+        self.assertTrue(raster_layer2.isValid())
+        project.addMapLayer(raster_layer2)
+        self.assertEqual(
+            QgsElevationUtils.significantZValuesForProject(project),
+            [103.1, 106.8, 116.8, 126.8])
+
+        props = raster_layer2.elevationProperties()
+        props.setEnabled(True)
+        props.setMode(Qgis.RasterElevationMode.FixedRangePerBand)
+        props.setFixedRangePerBand({1: QgsDoubleRange(103.1, 106.8),
+                                   2: QgsDoubleRange(106.8, 116.8),
+                                   3: QgsDoubleRange(126.8, 136.8)})
+        self.assertEqual(
+            QgsElevationUtils.significantZValuesForProject(project),
+            [103.1, 106.8, 116.8, 126.8, 136.8])
+
+
+if __name__ == '__main__':
+    unittest.main()