Get elevation of GeoTIFF using GDAL bindings in Java

Question

I'd like to read an elevation value from a GeoTIFF that I have. It's already working, but I'd like to interpolate the values for better results.

I currently do so like this:

Dataset dataset = gdal.Open(pathToGeoTiffFile, 0);
String projection = dataset.GetProjection();
double[] transform = dataset.GetGeoTransform();

SpatialReference src = new SpatialReference();
src.SetWellKnownGeogCS("WGS84");
SpatialReference dst = new SpatialReference(projection);
CoordinateTransformation coordinateTransformation = new CoordinateTransformation(src, dst);


double[] xy = coordinateTransformation.TransformPoint(lng, lat);

float[] result = new float[1];
int[] band = {1};

int x = (int)(((xy[0] - transform[0]) / transform[1]) - 0.5);
int y = (int)(((xy[1] - transform[3]) / transform[5]) - 0.5);

dataset.ReadRaster(x, y, 1, 1, 1, 1, 6, result, band);

double elevation = result[0];

This basically works, but there is no interpolation. So basically a coordinate gets mapped to a pixel (no matter if it's close to the next pixel or not) and then I take that value. But I'd prefer to interpolate the value. So if I am on. f.e the bottom of a pixel and the next pixel underneath has a different elevation, the value that I return should be interpolated.

I could of course calculate that on my own, but I was wondering if there is a function that I am missing?

Answer 1

There's Inverse Distance Weighting, which I tripped over recently:

https://pro.arcgis.com/en/pro-app/latest/tool-reference/3d-analyst/how-idw-works.htm

Basically, you take a set of points p with known elevations (say, the four pixel centers surrounding your position) and calculate:

A = Sum of p.elevation / distance(pos, p) for all p B = Sum of 1 / distance(pos, p) for all p

Interpolated elevation = A/B

You can change the weighting by raising distance(pos, p) to a power.