[GIS] Getting z-Value from xy-Values within IPolygon using ArcObjects

arcgis-10.0arcobjects

How can I get the z-Value of given xy-Values within an IPolygon?

I have an IPolygon, which is zAware. For given xy-Values I want to get the z-Value of the Polygon-Shape. What I want to do is something like intersecting the Polygon with an vertical line and getting the Intersecting Point.

Has anyone an idea how to do something like this?

Best Answer

There is no Inbuilt way to do this. A z-aware polygon, is fundamentally not 3 D in itself. What is Z Aware are the vertices. So for a point inside the polygon (i.e. inside in the sense of X-Y domain) no Z value is defined.

(If you having problems, visualizing this, imagine a z aware polygon that does not lie in one plane. Some points are on that plane, some above and some below. For this polygon, only the vertices have a defined z value, and not any points in the interior.)

So you can proceed in several ways:

If you are assuming that the vertices are sort of spot heights, then the inside of the polygon is the surface in between the points is the 3 dimensional surface which is defined by these spots heights.
Another way would be to convert this geometry into a Multipatch, where the surfaces are defined as triangles. There you can find the z value at any point.

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[GIS] Determining if mouse click falls within polygon using ArcObjects

As Peter Krebs has suggested on mouse down use IDisplayTransformation.ToMapPoint to assign the XY info to a point graphic. You can then use that graphic as a selector against your polygon layer.

public override void OnMouseDown(int Button, int Shift, System.Int32 X, System.Int32 Y)
{
    //MyBase.OnMouseDown(Button, Shift, X, Y)
    try {
        IMxApplication pMxApp = null;
        IActiveView ActiveView = default(IActiveView);

        pMxApp = (IMxApplication)m_App;

        m_MxDoc = (IMxDocument)m_App.Document;
        m_mxDocument = (MxDocument)m_App.Document;
        ActiveView = (IActiveView)(Map)m_MxDoc.FocusMap;

        IMap pMap = default(IMap);
        ISpatialReference pSpatialRef = default(ISpatialReference);

        pMap = m_MxDoc.FocusMap;
        pSpatialRef = pMap.SpatialReference;

        IScreenDisplay m_pDisplay = ActiveView.ScreenDisplay;

        m_pDisplay.StartDrawing(m_pDisplay.hDC, Convert.ToInt16(esriScreenCache.esriNoScreenCache));
        ISimpleMarkerSymbol simpleMarkerSymbol = new SimpleMarkerSymbolClass();

        ISymbol symbol = simpleMarkerSymbol as ISymbol;
        // Dynamic Cast
        m_pDisplay.SetSymbol(symbol);
        IDisplayTransformation displayTransformation = m_pDisplay.DisplayTransformation;

        // X and Y are in device coordinates
        m_Point = displayTransformation.ToMapPoint(X, Y);

        m_pDisplay.DrawPoint(m_Point);
        m_pDisplay.FinishDrawing();

        SelectFeature();

    } catch (Exception ex) {
        MessageBox.Show("Caught an unspecified error in the calling code: " + Constants.vbCrLf + ex.ToString());
    }

}



public void SelectFeature()
{
    //SelectFeature
    try {
        ILayer pLayer = default(ILayer);
        IActiveView pActiveView = default(IActiveView);
        IEnvelope pEnvelope = default(IEnvelope);
        ISpatialFilter pSF = default(ISpatialFilter);
        IEnumLayer pEnumLayer = default(IEnumLayer);

        m_MxDoc = (IMxDocument)m_App.Document;
        m_mxDocument = (MxDocument)m_App.Document;
        m_map = (Map)m_MxDoc.FocusMap;

        pActiveView = (IActiveView)m_map;
        if (m_map.LayerCount == 0)
            return;

        pEnumLayer = m_map.Layers;

        pLayer = pEnumLayer.Next;
        while (!(pLayer == null)) {
            if (pLayer.Name == "My Polygon Layer") {
                m_FLayer = (IFeatureLayer)pLayer;
            } else {
                return;
            }
            pLayer = pEnumLayer.Next;
        }

        m_FSel = (IFeatureSelection)m_FLayer;
        //Expand the points envelope to give better search results
        pEnvelope = m_MxDoc.CurrentLocation.Envelope;
        pEnvelope.Expand(m_MxDoc.SearchTolerance, m_MxDoc.SearchTolerance, false);
        pSF = new SpatialFilter();
        pSF.Geometry = pEnvelope;
        pSF.SpatialRel = esriSpatialRelEnum.esriSpatialRelIntersects;
        pSF.GeometryField = m_FLayer.FeatureClass.ShapeFieldName;

        //Refresh the old selection to erase it
        //pActiveView.PartialRefresh(esriViewDrawPhase.esriViewGeoSelection, Nothing, Nothing)
        //Perform the selection using a point created on mouse down
        m_FSel.SelectFeatures(pSF, esriSelectionResultEnum.esriSelectionResultNew, false);

        ISelectionSet pSelSet2 = default(ISelectionSet);
        // Draw all selected features.
        pSelSet2 = m_FSel.SelectionSet;

        if (pSelSet2.Count == 0) {
            MessageBox.Show("Polygon not selected");
        } else {
            MessageBox.Show("Polygon selected");
        }

        //Refresh again to draw the new selection
        pActiveView.PartialRefresh(esriViewDrawPhase.esriViewGeoSelection, null, null);
    } catch (Exception ex) {
        MessageBox.Show("Caught an unspecified error in the calling code: " + Constants.vbCrLf + ex.ToString());
    }

}

[GIS] Problem creating polygon features using ArcObjects / ArcGIS 10

Add the points in a clockwise order.

When you call IPointCollection.AddPoint, on a polygon the point is added to the exterior ring of the polygon. Vertices in exterior rings are expected to be clockwise, so if you don't add them in clockwise order ArcObjects will need to do more work to re-order them.

Interior rings (e.g. donut holes) are counter-clockwise.

Best Answer

Related Solutions

[GIS] Determining if mouse click falls within polygon using ArcObjects

[GIS] Problem creating polygon features using ArcObjects / ArcGIS 10

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