BEAM-DIMAP tie_point_grids

Is the step size for the tie_point_grids documented anywhere?
It would be nice if this was explicit and configurable somewhere, but I haven’t been able to find it.
I’m hoping someone can point me in the right direction :slight_smile:

-Thomas-

The step-size usually depends on the input data. In general tie-point grids are read form some file which defines the step-size. But it could be generated by API too. Maybe by some processing step.
But there is no user option to define the stepping.

Thank you for the quick response!
Is there a simple way I could find out which step size is used for a given data type (for example Sentinel-1 SAFE)? Where do I need to look in the source code to find this?
It would be great if the tie_point_grids folder contained explicit image row and column indices! Is there some reason why this is not included?

The tie-point grids are desribed in detail in the *.dim file.

This is a snippet from a Sentinel-3 OLCI stored as BEAM-DIMAP:

    <Tie_Point_Grids>
        <NUM_TIE_POINT_GRIDS>37</NUM_TIE_POINT_GRIDS>
        <Tie_Point_Grid_Info>
            <TIE_POINT_GRID_INDEX>0</TIE_POINT_GRID_INDEX>
            <TIE_POINT_DESCRIPTION>Latitude</TIE_POINT_DESCRIPTION>
            <PHYSICAL_UNIT>degrees_north</PHYSICAL_UNIT>
            <TIE_POINT_GRID_NAME>TP_latitude</TIE_POINT_GRID_NAME>
            <DATA_TYPE>float32</DATA_TYPE>
            <NCOLS>77</NCOLS>
            <NROWS>4091</NROWS>
            <OFFSET_X>0.0</OFFSET_X>
            <OFFSET_Y>0.0</OFFSET_Y>
            <STEP_X>64.0</STEP_X>
            <STEP_Y>1.0</STEP_Y>
            <CYCLIC>true</CYCLIC>
        </Tie_Point_Grid_Info>
        <Tie_Point_Grid_Info>

You will find similar information in the file for your Sentinel-1 product.
Where this information is located in the Sentinel-1 data, I don’t know.
Maybe @lveci can tell.

Hello,

Just sharing. You may be interested in my tool which extracts the tie point grid data from Sentinel-1 and then visualizes it. However, it only gets the corners of the burst so it can create a polygon. It does not load every single point:

1 Like

Oh, I see. Thanks a lot, very useful information! That seems to be what I need.

Nice project :slight_smile: