Layer stackin in SNAP for Sentinel 2

yousra · March 14, 2018, 8:36am

Hello,
Thank you @marpet for this precisons but could you please clarify how the iteration works? is it based on distance or geographic coordinates? I don’t understand "tries to find the closest pixel in the slave product " . Thank you in advance for your answer!

marpet · March 14, 2018, 9:03am

How the pixels are “found” in the source is dependent on the source product. Which kind of Geocoding it uses. Since Sentinel-2 is reprojected a mathematical transformation can be applied.
The geo-location from the master is picked up and the transformation is applied to get the pixel location in the slave product.
Following pointer into the code, if you are interested:

github.com

senbox-org/snap-engine/blob/94215622a4b4dc093f440750413ec6914793e6dd/snap-collocation/src/main/java/org/esa/snap/collocation/CollocateOp.java#L331


private void validateProduct(Product product) {
    ensureSceneGeoCoding(product);
    ensureSingleRasterSize(product);
}


@Override
public void computeTileStack(Map<Band, Tile> targetTileMap, Rectangle targetRectangle, ProgressMonitor pm) throws
        OperatorException {
    pm.beginTask("Collocating bands...", targetProduct.getNumBands() + 1);
    try {
        final PixelPos[] sourcePixelPositions = ProductUtils.computeSourcePixelCoordinates(
                slaveProduct.getSceneGeoCoding(),
                slaveProduct.getSceneRasterWidth(),
                slaveProduct.getSceneRasterHeight(),
                masterProduct.getSceneGeoCoding(),
                targetRectangle);
        final Rectangle sourceRectangle = getBoundingBox(
                sourcePixelPositions,
                slaveProduct.getSceneRasterWidth(),
                slaveProduct.getSceneRasterHeight());
        pm.worked(1);

github.com

senbox-org/snap-engine/blob/aa5bc12256c87dbcfccb452b8e8cf523414a8ac0/snap-core/src/main/java/org/esa/snap/core/datamodel/CrsGeoCoding.java#L236-L238


DirectPosition directGeoPos = new DirectPosition2D(geoPos.getLon(), geoPos.getLat());
DirectPosition directPixelPos = geoToImage.transform(directGeoPos, null);
pixelPos.setLocation(directPixelPos.getOrdinate(0), directPixelPos.getOrdinate(1));

yousra · March 14, 2018, 10:24am

Thank you @marpet for your quick answer

psoglia · October 9, 2022, 11:16am

Is it possible to set the components to have the name of the slave product as pattern, instead of the ID? I cannot find a list of possible “variables” except for ${SLAVE_NUMBER_ID}

marpet · October 10, 2022, 6:43am

At the moment the SLAVE_NUMBER_ID is the only variable you can use.