ArcGIS, Calibrating routes, interpolation error

Question

I know that copy a question is not exactly great way to ask on this forum, but my situation is exactly the same as this unresolved issue on the (closed) ESRI forum:

I have a stream centreline (fairly curvy) which can be converted to a route. I have a few points on that line which have stream bed elevation. The bed elevation varies along the stream, and does not necessarily increase as you go up the stream (e.g., goes up and down a little bit).

I want to calibrate the route using the bed elevations, so that I can interpolate an elevation value between the known points.

When I attempt to calibrate the stream route with the known points, it appears to work. But if I examine the measure values of individual vertices along the route, they are incorrect. Vertices that fall exactly where there is a known value (a calibration point) have the correct elevation, but vertices between the known points have incorrect values. The incorrect values are not 0, which makes me think it is calculating a value somehow. But it is not doing as I expect.

For example, between known points of 3.11 and 3.56, you'd expect values between 3.11 and 3.56. Instead, I might get values of 3.78, 3.78, 3.78, 3.79, etc.

May be it can be resolved in here.

Best regards Tomek

Answer 1

It looks to me like there's a bug in IMSegmentation3.CalibrateByMs for v10.0 sp2. When I create a diagonal polyline from 0.0,0.0 to 10.0,10.0 with unknown measures at its vertices, then calibrate it, I would expect to see all vertices have measures - not just the ones inserted.

Update

Oops, I had forgot to call CalculateNonSimpleMs, after adding it, I get this output. I would expect to see a measure of 100.0 at 10.0,10.0 - not 62.5. I think this is a bug.

split 2.5,2.5,100.0
split 5.0,5.0,50.0
split 7.5,7.5,75.0
0.0,0.0,112.5 (BUG)
2.5,2.5,100.0
5.0,5.0,50.0
6.0,6.0,60.0 (CORRECT)
7.5,7.5,75.0
10.0,10.0,62.5 (BUG)
Measure at 0.55 is 55.00000001234

Here's the c# code:

public static void TestPolylineM(ISpatialReference sr)
{    
    var calibrationPts = new MultipointClass() as IPointCollection;
    ((IMAware)calibrationPts).MAware = true;
    ((IGeometry)calibrationPts).SpatialReference = sr;

    //                                  x    y    m
    calibrationPts.AddPoint(MakePointM(2.5, 2.5, 100.0, sr));
    calibrationPts.AddPoint(MakePointM(5.0, 5.0, 50.0, sr));
    calibrationPts.AddPoint(MakePointM(7.5, 7.5, 75.0, sr));

    IPointCollection pc = new PolylineClass();
    ((IGeometry)pc).SpatialReference = sr;
    ((IMAware)pc).MAware = true;
    pc.AddPoint(MakePointM(0.0, 0.0, double.NaN, sr));
    pc.AddPoint(MakePointM(6.0, 6.0, double.NaN, sr));
    pc.AddPoint(MakePointM(10.0, 10.0, double.NaN, sr));

    var mseg = pc as IMSegmentation3;

    int how = (int) (esriGeometryUpdateMEnum.esriGeometryInterpolate 
        | esriGeometryUpdateMEnum.esriGeometryExtrapolateAfter 
        | esriGeometryUpdateMEnum.esriGeometryExtrapolateBefore);

    Simplify((IGeometry)pc);
    double cutoffDistance = 1.0;

    var splitPoints = mseg.CalibrateByMs(calibrationPts.EnumVertices, how, cutoffDistance);
    mseg.CalculateNonSimpleMs();
    ListSplits(splitPoints);


    for (int i = 0; i < pc.PointCount; i++)
    {
        var pnt = pc.get_Point(i);
        Debug.Print("{0:0.0},{1:0.0},{2:0.0}", pnt.X, pnt.Y, pnt.M);
    }

    double distAlong = 0.55;
    var measures = mseg.GetMsAtDistance(distAlong, true) as double[];
    Debug.Print("Measure at {0} is {1}", distAlong, measures[0]);
}

public static IPoint MakePointM(double x, double y,double m, ISpatialReference sr)
{
    IPoint pnt = new PointClass();
    ((IMAware)pnt).MAware = true;
    pnt.SpatialReference = sr;
    pnt.PutCoords(x, y);
    if(!Double.IsNaN(m))
        pnt.M = m;
    return pnt;
}

public static void ListSplits(IEnumSplitPoint splitPoints)
{
    IPoint splitPoint;
    int partIndex;
    int vertexIndex;
    splitPoints.Next(out splitPoint, out partIndex, out vertexIndex);
    while (splitPoint != null)
    {
        Debug.Print("split {0:0.0},{1:0.0},{2:0.0}", splitPoint.X, splitPoint.Y, splitPoint.M);
        splitPoints.Next(out splitPoint, out partIndex, out vertexIndex);
    }

}
public static void Simplify(IGeometry geom)
{
    var topoOp = geom as ITopologicalOperator2;
    if (topoOp != null)
    {
        topoOp.IsKnownSimple_2 = false;
        topoOp.Simplify();
    }
}

Answer 2

This is a bug, it's been causing me problems for years. And yes, there is a workaround -- but a tedious one. I've been in touch with ESRI Canada about this, they replicated the bug, and have told me that Esri US is working on it... I'm not sure if that means a fix for 10.1 or later. Bug is NIM069049 (you can search for that on Esri's web site, but it doesn't give you much info). The bug applies to the Calibrate Routes tool. I get it when I'm working with stream bed elevations or water surface elevations -- values that don't necessarily always increase or decrease along the line, and that are not related to the line length. I don't have problems with the Calibrate Routes tool for values that are related to line length, such as calculating chainage (mileposts). A workaround is to do the calibration manually. Manual calibration takes a lot longer than using the Calibrate Routes tool, but it does work. If you don't know how to calibrate manually, there's a tutorial. At 9.3, the link is: http://webhelp.esri.com/arcgisdesktop/9.3/pdf/linear_referencing_tutorial.pdf For 10, the link is: http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Exercise_5_Editing_routes/00390000004p000000/ Checkout the last section, Recalibrating a Route.