Reprojection Creates Ghost Pixels Far Away

Hello,

I have encountered a bug while reprojecting an OLCI EFR scene which seems to be adding ghost pixels very far away from the scene center. I have noticed this for quite a number of scenes when attempting to reproject and wondering if this is a bug or that I am missing something.

–Edit–
It seems that turning off per-pixel geocoding (using the tie point grids) fixes this issue.

Source product: S3A_OL_1_EFR____20180527T193613_20180527T193913_20180604T114027_0179_031_327_3420_LN1_O_NT_002.SEN3

Script: (With per-pixel geo-coordinates enabled)
→ Read
→ Subset (e.g. select Oa01 radiance)
→ Reproject (To Geographic Lat/Lon WGS84 or Auto UTM)
→ Write (BEAM-DIMAP)

Source image bounding box according to the source geo_coordinates.nc (the sci hub footprint also agrees with this)
Upper Left lon/lat (degrees): -160.42,-20.58
Lower Right lon/lat (degrees): -144.45,-34.05

Output bounding box (via gdal):
Upper Left (-168.8932150, -18.7364568) (168d53’35.57"W, 18d44’11.24"S)
Lower Right ( 160.5098426, -49.0349038) (160d30’35.43"E, 49d 2’ 5.65"S)

Footprint

If anyone else has encountered this issue and guidance would be appreciated.

Hi,

this issue is now recorded in our issue tracker (SNAP-954).

We know that the pixel-based GeoCoding has some issues, especially when reprojecting the data.
That’s why we recently started a dedicated task to improve it. Unfortunately, the current situation does not allow us to spent much time on it. I hope this will change soon.

Maybe in early October, I can have a look at this particular issue, to lower the problem at least.
But quick-fixes will probably not help much.

The tie-points work better, as you have noticed, when reprojecting the data. But the accuracy of the tie-points is not very high, unfortunately, this is inherent to the provided data.

Ciao

1 Like

Side note: Do NOT turn off per-pixel geocoding when reprojecting S3 OLCI products - you might experience a random geometric shift in the reprojected image (at least I did).

Marco - any news on the bug? (I can’t comment there.)

No, not yet, unfortunately But we want to fix it till the next major release.

Quarterly check on the status of this bug…

Marco - any news on the fix? https://senbox.atlassian.net/browse/SNAP-954 is still open.

Thanks,
Simon

Unfortunately not, priorities have changed and therefore it is not in the next release, again … :frowning:

Marco - Ok, I see. Is there a new ETA, by any chance?

Thanks,
Simon

Sorry, but I don’t dare to give an ETA. But we are not giving up and soon we will start on this issue again.

Marco - any news on this issue?

Thanks,
Simon

Just that we are working on it.