[GIS] Find minimum elevation along a polyline and return xy or point

arcgis-10.1demelevationlinepython-2.7

Using ArcGIS 10.1 and Python IDLE 2.7.2…

I'm trying to find the minimum value of a polyline with a raster layer and turn that LOCATION into a point. I put everything together in model builder, but the raster calculator doesn't like 32-bit floating points, which is what my DEM is. I tried to get around the raster calculator with the Con tool in python, but I believe an attribute table is required for this (which I don't have due to floating point). I could convert the DEM to integer and build one, but this is already a lengthy process that involves many scripts and tools and wanted to see if anyone else out there had any thoughts? I'm open to any anything, really, conversion of polyline to polygon, etc…attaching a screenshot of modelbuilder process that works, but I need a script as I am doing this 1000+ times. enter image description here

I can turn the polyline into a 3D feature and find the minimum value, but I don't know how to find WHERE that minimum value is. If I could locate it with XY coordinates, I can then generate the point.

Thoughts? If I'm wrong about the Con tool and my syntax is wrong, that would be awesome, so please feel free to suggest something. It finds where the min is along the polyline that has been converted to raster and where that min is within the DEM, thus returning a min pixel:

tempRas1 = Con(Raster(LG_DEM_0_tif == LG_0_Zonalmin_img), LG_DEM_0_tif)

Best Answer

This is how I would do it:

Convert your line to a raster (Polyline to Raster)
Convert the raster to points (Raster to Point)
Add Z value from the raster to the points (Extract Values to Points). A new field named RASTERVALU with the raster Z value is added.
Turn the points into a feature layer and select the point with the minimum Z field value using for example Select Layer by Attributes and an expression like [RASTERVALU] in (SELECT min( [RASTERVALU] ) FROM points_Z). See here for more details on Select min/max values with Select By Attributes.

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[GIS] Finding point with highest elevation in area using ArcObjects

Thanks to Vince's comments I was able to perform succesfully the whole process.

As I wrote, first I wanted to establish a number of AOIs on the raster. Nothing fancy here, I got raster properties by using this small function below:

public static IRasterProps GetRasterProperties(IRasterDataset rasterDataset, int rasterBandIndex)
{
     IRasterBandCollection rasterBands = (IRasterBandCollection)rasterDataset;
     var rasterBand = rasterBands.Item(rasterBandIndex);
     return (IRasterProps)rasterBand;
}

Given the raster properties, I created a number of areas each defined by an IEnvelope. In order to split the input raster to AOIs, I used the ExtractByRectangle Geoprocessing tool.

ExtractByRectangle extract = new ExtractByRectangle(inputRaster, envelope, path);
IGeoProcessorResult2 result = gp.Execute(extract, null) as IGeoProcessorResult2;

parameters:
inputRaster - IRasterDataset (input raster)
envelope - IEnvelope (definition of our AOI)
path - file path to resulting raster

I won't describe all Geoprocessing shenanigans, but that is where ArcObjects get very cryptic in my opinion. A number of error codes that have no obvious explanation doesn't help too. I found great code by Kirk Kuykendall that helps a lot with debugging here: Avoiding fails from ArcObjects geoprocessing with .NET?

Now, we have our small raster AOIs. I need to get the point of maximal elevation for each of them. Hence, I start with computing statistics for every AOI using the function below:

public void ComputeRasterStatistics(IRasterDataset rasterDataset, int rasterBandIndex)
{
     IRasterBandCollection rasterBands = (IRasterBandCollection)rasterDataset;
     var rasterBand = rasterBands.Item(rasterBandIndex);
     RasterStatistics = rasterBand.Statistics;
}

Statistics deliver information concerning values of raster extremes, inclusing the maximum point value of a raster. Next I convert the raster to points using the function below.

public static IFeatureClass RasterToPoints(IRasterDataset raster)
{
     IConversionOp conversionOp = new RasterConversionOpClass();
     IWorkspace shapeWS = FeatureWorkspaceHelper.CreateInMemoryWorkspace();
     var featClass = conversionOp.RasterDataToPointFeatureData((IGeoDataset)raster, shapeWS, Guid.NewGuid().ToString());
     return (IFeatureClass)featClass;
}

FeatureWorkspaceHelper.CreateInMemoryWorkspace(); is a helper function of mine, that creates an empty in-memory workspace. Have in mind this can be obviously done with 'classic' file workspace too.

Now I just need to find a point that has the maximal elevation and return it. The function below (some hardcodes there!) does that.

private IPoint GetRasterMaxElevationPoint(IFeatureClass featureClass, double val, int elevationIndex)
{
    IQueryFilter queryFilter=new QueryFilterClass();
    queryFilter.WhereClause = "GRID_CODE >= " + (val - 0.01).ToString();

    var cursor = featureClass.Search(queryFilter, true);
    IFeature feature = null;
    IGeometry shape = null;
    double maxValue = double.MinValue;
    while ((feature = cursor.NextFeature()) != null)
    {
        if ((double) feature.Value[elevationIndex] > maxValue)
        {
            shape = feature.Shape;
            maxValue = (double) feature.Value[elevationIndex];
        }
    }

    return new PointClass()
    {
        X = shape.Envelope.LowerLeft.X,
        Y = shape.Envelope.LowerLeft.Y,
        SpatialReference = shape.SpatialReference
    };
}

Best Answer

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