Problems with mosaicing of processed images

snap Problem Reports
1

Dear all,
there are some problems with the mosaicing function (Raster>Geometric operations>Mosaicing).

  1. I receive an arror while attempting to mosaic some Cosmo-Skymed images already pre-processed by SNAP (i.e. in .din format). If I selected a predefined CRS (in particular EPSG:3031) I got a popup saying: “No Coordinate Reference System” selected. Also, if I choose another CRS from the “Custom CRS”, I perform the mosaic, then I reattempt to masaicing using the predefined 3031 CRS, everything seems to work. However I don’t know if this happens because SNAP has in memory the previous CRS used or because this workaround worked.
  2. Independently of the pixel size of the images to be mosaiced and the value I set in “Mosaic bounds”>“Pixel Size”, the final mosaiced image comes out at a very coarse resolution, probably 1km or 0.05°.

It can be useful to say that I am using SNAP 7.0.0 but the bugs were present also in older versions.

I hope someone can fix these bugs. Thanks!

2

Did you try up to mosaic and then reproject the result to see if it make sense!

Also check up this video, but it’s talking about S2 multi size mos. might be helps,

Source of the post

And this one Mosaic,

Source : https://www.youtube.com/watch?v=PTmLs9BRSKE

3

Dear falahfakhri,
thanks for your very quick reply. I appreciate it a lot.
About your suggetions: no, I haven’t try the reprojection given I can do the operation (which is just one-time for me) easily in Qgis without this double step. Also, the video says that I can change the resolution of the final mosaic by setting the required “Pixel size” values. This confirms that what I am pointing out are actually bugs that must be fixed.
Unfortunately I haven’t found a better place to report this couple of stupid bugs than the forum.

Thanks again,
Marco

4

Hi Marco,

this is the best place to report problems. We developers watch this forum.

I can confirm that there is an issue with the selection of a predefined CRS. I had the same problems as you. (SNAP-1158)

If you configure the mosaic, like in the following, it should do the same as EPSG:3031.

image
image.png552×681 68.3 KB

The specified pixel size was considered when I made a mosaic. This worked for me.
1km and 0.05° are the default values, depending on the projection.

5

With the next update, the predefined CRS issue (SNAP-1158) should be fixed. Not sure when this will be released, but shouldn’t take too long.

1 Like
6

Thanks, this will be very useful. Especially with the students.