Formula that the collocate tool uses

pamochungo · March 15, 2018, 2:45pm

Hi. Does anyone know the formula that the Collocate tool uses? with Bilinear interpolation?

arus · March 16, 2018, 4:18am

Yes, even I wanted to know the formula used there.

marpet · April 3, 2018, 7:51am

It is not easy to express this in a simple formula.

But you can have a look at the code:
Here the general Collocation is done:

github.com

senbox-org/snap-engine/blob/94215622a4b4dc093f440750413ec6914793e6dd/snap-collocation/src/main/java/org/esa/snap/collocation/CollocateOp.java#L391


        targetTile.setRawSamples(getSourceTile(sourceRaster, targetTile.getRectangle()).getRawSamples());
    }
}


@Override
public void dispose() {
    sourceRasterMap = null;
    super.dispose();
}


private void collocateSourceBand(RasterDataNode sourceBand, Rectangle sourceRectangle,
                                 PixelPos[] sourcePixelPositions,
                                 Tile targetTile, ProgressMonitor pm) throws OperatorException {
    pm.beginTask(format("collocating band {0}", sourceBand.getName()), targetTile.getHeight());
    try {
        final RasterDataNode targetBand = targetTile.getRasterDataNode();
        final Rectangle targetRectangle = targetTile.getRectangle();


        final int sourceRasterHeight = slaveProduct.getSceneRasterHeight();
        final int sourceRasterWidth = slaveProduct.getSceneRasterWidth();

And this is how the interpolation is implemented:

github.com

senbox-org/snap-engine/blob/26835de0a8b83ab88b3571932535df9a0f68c295/snap-core/src/main/java/org/esa/snap/core/dataop/resamp/BilinearInterpolationResampling.java#L30




public String getName() {
    return "BILINEAR_INTERPOLATION";
}


public final Index createIndex() {
    return new Index(2, 1);
}


// Compute resampling index for given pixel coordinate assuming that the pixel intensity is located at its center.
public final void computeIndex(final double x,
                               final double y,
                               final int width,
                               final int height,
                               final Index index) {
    index.x = x;
    index.y = y;
    index.width = width;
    index.height = height;


    final int i0 = (int) Math.floor(x);

pamochungo · April 4, 2018, 3:17pm

Thanks Marpet! Let me see what I can make out of this code.