By default, QgsProjectionSelectionTreeWidget should only

show horizontal (and compound) CRS in order to match behavior
of older releases

But allow opt in filters for display of vertical crs

python/gui/auto_generated/qgscoordinatereferencesystemmodel.sip.in

@@ -172,6 +172,9 @@ Returns whether deprecated CRS will be filtered from the results.
 
 };
 
+QFlags<QgsCoordinateReferenceSystemProxyModel::Filter> operator|(QgsCoordinateReferenceSystemProxyModel::Filter f1, QFlags<QgsCoordinateReferenceSystemProxyModel::Filter> f2);
+
+
 
 /************************************************************************
  * This file has been generated automatically from                      *

python/gui/auto_generated/qgsprojectionselectiontreewidget.sip.in

@@ -32,9 +32,14 @@ suitable to use the compact :py:class:`QgsProjectionSelectionWidget` widget.
 %End
   public:
 
-    QgsProjectionSelectionTreeWidget( QWidget *parent /TransferThis/ = 0 );
+    QgsProjectionSelectionTreeWidget( QWidget *parent /TransferThis/ = 0,
+                                      QgsCoordinateReferenceSystemProxyModel::Filters filters = QgsCoordinateReferenceSystemProxyModel::FilterHorizontal | QgsCoordinateReferenceSystemProxyModel::FilterCompound );
 %Docstring
-Constructor for QgsProjectionSelectionTreeWidget.
+Constructor for QgsProjectionSelectionTreeWidget, with the specified ``parent`` widget.
+
+Since QGIS 3.34, the optional ``filter`` argument can be used to specify filters on the systems
+shown in the widget. The default is to show all horizontal and compound CRS in order to match
+the behavior of older QGIS releases. The ``filter`` can be altered to also include vertical CRS if desired.
 %End
 
     ~QgsProjectionSelectionTreeWidget();
@@ -109,6 +114,24 @@ The initial "preview" rectangle for the bounds overview map.
 .. seealso:: :py:func:`previewRect`
 
 .. versionadded:: 3.0
+%End
+
+    QgsCoordinateReferenceSystemProxyModel::Filters filters() const;
+%Docstring
+Returns the filters set on the available CRS.
+
+.. seealso:: :py:func:`setFilters`
+
+.. versionadded:: 3.34
+%End
+
+    void setFilters( QgsCoordinateReferenceSystemProxyModel::Filters filters );
+%Docstring
+Sets ``filters`` for the available CRS.
+
+.. seealso:: :py:func:`filters`
+
+.. versionadded:: 3.34
 %End
 
   public slots:

src/gui/qgscoordinatereferencesystemmodel.h

@@ -397,5 +397,7 @@ class GUI_EXPORT QgsCoordinateReferenceSystemProxyModel: public QSortFilterProxy
     Filters mFilters = Filters();
 };
 
+Q_DECLARE_OPERATORS_FOR_FLAGS( QgsCoordinateReferenceSystemProxyModel::Filters )
+
 
 #endif // QGSCOORDINATEREFERENCESYSTEMMODEL_H

src/gui/qgsprojectionselectiontreewidget.cpp

@@ -36,12 +36,14 @@
 #include <QMessageBox>
 #include <QRegularExpression>
 
-QgsProjectionSelectionTreeWidget::QgsProjectionSelectionTreeWidget( QWidget *parent )
+QgsProjectionSelectionTreeWidget::QgsProjectionSelectionTreeWidget( QWidget *parent, QgsCoordinateReferenceSystemProxyModel::Filters filters )
   : QWidget( parent )
 {
   setupUi( this );
 
   mCrsModel = new QgsCoordinateReferenceSystemProxyModel( this );
+  mCrsModel->setFilters( filters );
+
   lstCoordinateSystems->setModel( mCrsModel );
   lstCoordinateSystems->setSelectionBehavior( QAbstractItemView::SelectRows );
 
@@ -253,6 +255,16 @@ QgsRectangle QgsProjectionSelectionTreeWidget::previewRect() const
   return mAreaCanvas->canvasRect();
 }
 
+QgsCoordinateReferenceSystemProxyModel::Filters QgsProjectionSelectionTreeWidget::filters() const
+{
+  return mCrsModel->filters();
+}
+
+void QgsProjectionSelectionTreeWidget::setFilters( QgsCoordinateReferenceSystemProxyModel::Filters filters )
+{
+  mCrsModel->setFilters( filters );
+}
+
 QgsCoordinateReferenceSystem QgsProjectionSelectionTreeWidget::crs() const
 {
   if ( mCheckBoxNoProjection->isEnabled() && mCheckBoxNoProjection->isChecked() )

src/gui/qgsprojectionselectiontreewidget.h

@@ -19,9 +19,9 @@
 #include "qgis_sip.h"
 #include "qgis_gui.h"
 #include "qgscoordinatereferencesystem.h"
+#include "qgscoordinatereferencesystemmodel.h"
 
 class QResizeEvent;
-class QgsCoordinateReferenceSystemProxyModel;
 
 /**
  * \class QgsProjectionSelectionTreeWidget
@@ -44,9 +44,14 @@ class GUI_EXPORT QgsProjectionSelectionTreeWidget : public QWidget, private Ui::
   public:
 
     /**
-     * Constructor for QgsProjectionSelectionTreeWidget.
+     * Constructor for QgsProjectionSelectionTreeWidget, with the specified \a parent widget.
+     *
+     * Since QGIS 3.34, the optional \a filter argument can be used to specify filters on the systems
+     * shown in the widget. The default is to show all horizontal and compound CRS in order to match
+     * the behavior of older QGIS releases. The \a filter can be altered to also include vertical CRS if desired.
      */
-    QgsProjectionSelectionTreeWidget( QWidget *parent SIP_TRANSFERTHIS = nullptr );
+    QgsProjectionSelectionTreeWidget( QWidget *parent SIP_TRANSFERTHIS = nullptr,
+                                      QgsCoordinateReferenceSystemProxyModel::Filters filters = QgsCoordinateReferenceSystemProxyModel::FilterHorizontal | QgsCoordinateReferenceSystemProxyModel::FilterCompound );
 
     ~QgsProjectionSelectionTreeWidget() override;
 
@@ -109,6 +114,22 @@ class GUI_EXPORT QgsProjectionSelectionTreeWidget : public QWidget, private Ui::
      */
     QgsRectangle previewRect() const;
 
+    /**
+     * Returns the filters set on the available CRS.
+     *
+     * \see setFilters()
+     * \since QGIS 3.34
+     */
+    QgsCoordinateReferenceSystemProxyModel::Filters filters() const;
+
+    /**
+     * Sets \a filters for the available CRS.
+     *
+     * \see filters()
+     * \since QGIS 3.34
+     */
+    void setFilters( QgsCoordinateReferenceSystemProxyModel::Filters filters );
+
   public slots:
 
     /**