Getting raster cell indexes from point coordinates

MarceloLago — Tue, 29 Oct 2013 17:55:43 GMT

Hi,

I have a point shape file (IFeatureLayer) and a raster file (IRaster) taken from an ArcMap project. My goal is to convert from the point coordinates to raster cell indexes. So, the following steps may be necessary

1) get coordinates (XF,YF) of each point in the feature layer
2) convert coordinates (XF,YF) to raster spatial reference (XR,YR)
3) convert from coordinates (XR,YR) to grid cell indexes (kXR,kYR) in raster file

I am not sure how to code these steps by using the ArcObjets .NET. I am using ArcMap 10.1 and coding in C#. If you could send me some hints or snippets for these steps, it would be greatly appreciated.

Thanks in advance for all your help, Marcelo.

Re: Getting raster cell indexes from point coordinates

martinmaretta — Wed, 30 Oct 2013 06:59:09 GMT

pRaster as IRaster2

x = pFeat.Extent.XMax() 'map coordinate
y = pFeat.Extent.YMax()

i = pRaster.ToPixelColumn(x) 'raster coordinate
j = pRaster.ToPixelRow(y)

value = pRaster.GetPixelValue(0, i, j)

Re: Getting raster cell indexes from point coordinates

MarceloLago — Tue, 05 Nov 2013 20:39:56 GMT

Hi again,

After the help above from Martin, the help from Jamie P. at ESRI Support Team, and a trial and error process, please find below a working C# code that solves this problem. If you find a better way to accomplish this, please let me know. Thanks!

private int getPoints(IRaster raster, IFeatureLayer featureLayer,
            out long[] kxR, out long[] kyR)
        {
            IRasterProps rasterProps = (IRasterProps)raster; // Raster properties

            // get coordinates (xF,yF) of each point in the feature layer ---------------------------------------
            IQueryFilter queryFilter = new QueryFilterClass(); // Set up the query by default
            int nP = featureLayer.FeatureClass.FeatureCount(queryFilter); // number of points
            Debug.Print("Number of points in shape file= " + nP.ToString());

            double[] xF = new double[nP];
            double[] yF = new double[nP];
            for (int kP = 0; kP < nP; kP++)
            {
                IFeature pF = featureLayer.FeatureClass.GetFeature(kP);
                xF[kP] = pF.Extent.XMax; // after help from Martin Maretta
                yF[kP] = pF.Extent.YMax;
                Debug.Print("Point " + kP.ToString() + " at (" + xF[kP].ToString() + "," + yF[kP].ToString() + ")");
            }

            // convert coordinates (xF,yF) to raster spatial reference (xR,yR) -----------------------------------
            double[] xR = new double[nP];
            double[] yR = new double[nP];
            IFields pFields = featureLayer.FeatureClass.Fields;
            ISpatialReference sr1 = pFields.Field[pFields.FindField(featureLayer.FeatureClass.ShapeFieldName)].GeometryDef.SpatialReference;
            ISpatialReference sr2 = rasterProps.SpatialReference;
            if (sr1.Name.Equals(sr2.Name,StringComparison.OrdinalIgnoreCase))
            {
                // spatial references are the same => no need of reprojection
                xR = xF;
                yR = yF;
            }
            else // after help from Jamie P. from ESRI Support Team
            {
                //Point to project
                IPoint point = new PointClass() as IPoint;
                for (int kP = 0; kP < nP; kP++)
                {
                    point.PutCoords(xF[kP], yF[kP]);
                    //Geometry Interface to do actual project
                    IGeometry geometry = point;
                    geometry.SpatialReference = sr1;
                    geometry.Project(sr2);
                    point = geometry as IPoint;
                    point.QueryCoords(out xR[kP], out yR[kP]);
                }
            }

            // convert from coordinates (xR,yR) to grid cell indexes (kxR,kyR) in raster file --------------------------
            IPnt cellSize = rasterProps.MeanCellSize();
            kxR = new long[nP];
            kyR = new long[nP];
            int kI = 0;
            for (int kP = 0; kP < nP; kP++)
            {
                kxR[kI] = (int)Math.Floor((xR[kP] - rasterProps.Extent.XMin) / cellSize.X); // x index starts at XMin
                kyR[kI] = (int)Math.Floor((rasterProps.Extent.YMax - yR[kP]) / cellSize.Y); // y index starts at YMax
                if (0 <= kxR[kI] && kxR[kI] < rasterProps.Width &&
                    0 <= kyR[kI] && kyR[kI] < rasterProps.Height)
                {
                    Debug.Print("Point " + kP.ToString() + " indexes= (" + kxR[kI].ToString() + "," + kyR[kI].ToString() + ") => Inside raster area");
                    kI++; // valid index
                }
                else
                {
                    Debug.Print("Point " + kP.ToString() + " indexes= (" + kxR[kI].ToString() + "," + kyR[kI].ToString() + ") => Outside raster area");
                }
            }
            Debug.Print("Number of points inside raster area= " + kI.ToString());

            if (kI < nP)
            {
                // some points were discarded => TODO: remove unused array space
                nP = kI;
            }

            return nP;
        }

Re: Getting raster cell indexes from point coordinates

ModyBuchbinder — Wed, 06 Nov 2013 04:13:48 GMT

In the VBA examples for 10.0 there was a great example: http://help.arcgis.com/en/sdk/10.0/vba_desktop/conceptualhelp/0001/000100000054000000.htm
You can try to translate it.

Have fun

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