Reproject and collocateWith graph example



I’m new to snap and trying to automate some data conversions with gpt. I’ve tried to understand the tutorial and the most helpful thread I’ve found on this topic so far ([here] (Best practice to convert and reproject Sentinel-3 radiances to reflectance)), along with gpt -h and gpt Reproject -h.

I can successfully extract a band (using BandExtract) and reproject the data using the Reproject example from the two links above. However, I cannot figure out the correct XML to reproject using collateWith and an existing HDF5 file I have.

In the GUI GraphBuilder and Reproject, I can’t find a way to set a collocateWith option. Am I missing something there? I only see “Custom” and “Predefined” CRS options.

In the GUI GraphBuilder and Collocate (is this even what I should be using?), I see an error (red text) that states, "Error: [NodeID Collocate] Operate ‘CollocateOp’: Mandatory source product (field ‘masterProduct’) not set.

Can someone provide a working example for this?

Thank you,



It seems that the UI for the Reprojection in the GraphBuiler is only half-way implemented and the collocateWith option is missing.

If you go to Raster -> Geometric Operations -> Reprojection you get the “main” Reprojection GUI.
Here you have the collocateWith option. It is only named as “Use CRS of”.
So this is not a real collocation but it brings both products to the same CRS.
Combining both product into one would be done with the Collocate operator. I would also suggest that you also use the one in Raster -> Geometric Operations.


Could you tell me where I can find the mathematics behind collocation tool ?


This is described in the Help

You can find more details in the code: