ship detection output

Microwave Toolbox
#1

This is related to using snappy python for ship detection in Sentinel-1 imagery. The algorithm itself works fine. At the end, I am saving the entire output as beam-dimap file with the following command

snappy.ProductIO.writeProduct(…, … , ‘BEAM-DIMAP’)

Among others, that includes a .csv file with ship detection data (latitude, longitude, ship width, ship length, etc.). This csv file (ShipDetections.csv) is compact sized and saved in the subfolder for vector data. I want to know whether it is possible to save this csv file only (rather than the entire output as beam-dimap). This would be much more efficient in terms of computational resources.

#2

Hello Claus,

I think it is currently not possible to just store the csv file at least not straight forward. The current implementation does not allow it.

As a strange workaround you could do the following. I write the code without testing it. So it might contain some errors and some gaps ‘…’, but the general approach should be clear.

// ship_detection = GPF.createProduct('Object-Discrimination', ...)
// after creating the ship_detection product you need to iterate over all bands and acquire the data.
// This triggers the actual computation.
bands = ship_detection.getBands()
for band in bands:
    band.getGeophysicalImage().getData()

// Now you can get the VectorDataNode
vdn = ship_detection.getgetVectorDataGroup().get('ShipDetections')

vdnWriter = jpy.get_type('org.esa.snap.core.dataio.geometry.VectorDataNodeWriter')
writer =vdnWriter()
writer.write(vdn, File('Path_to_location.csv'))

Maybe someone else has an easier idea. Maybe @lveci or @jun_lu?

1 Like
#3

A workaround for problems like this is to create a temporary store in RAM big enough to store the full BEAM-DIMAP file, save data you will need in the future (e.g., .csv, .dim for metadata, and perhaps additional processing history details) to permanent storage, and erase the RAM store.

#4

When testing the above, the line vdn = ship_detection.getgetVectorDataGroup().get(‘ShipDetections’)
gave the following error AttributeError: ‘org.esa.snap.core.datamodel.Product’ object has no attribute ‘getgetVectorDataGroup’

#5

I typed one get to much. Sorry.
It should be:

vdn = ship_detection.getVectorDataGroup().get(‘ShipDetections’)
#6

The line “writer.write(vdn, File(‘Path_to_location.csv’))” still gives some error. The first error was “NameError: global name ‘File’ is not defined”. Following that, we changed the line to “writer.write(vdn, ‘Path_to_location.csv’)”. The next error was “RuntimeError: no matching Java method overloads found”.

#7

I’m not sure if this causes the error, but you have to replace Path_to_location.csv with your personal target directory and filename.

#8

We did that.

#9

Before using File like this you need to import it.

from snappy import File

Or you can write snappy.File(‘Path_to_location.csv’)