Sentinel 1: Terrain Corrected - Subsetted image not aligning Geographically

s1tbx Problem Reports
#1

I was trying the subset an area from Sentinel 1 GRD zip file using the following graph builder and WKT coordinates.

Graph_builder: |690x83](upload://fQXurdeRwyuu5c7I1bxC15cuSei.jpeg)

WKT polygon coordinates:

POLYGON ((-6.633369 53.184910,-6.449935 53.190299,-6.446312 53.087612,-6.634983 53.081792,-6.633369 53.184910))

WKT_Extent
WKT_Extent.jpg1782×510 106 KB

As you could see in the image below, when I try to overlay the subsetted image in GIS it is not aligning correctly.

Untitled
Untitled.jpg3711×2727 1.51 MB

Surprisingly, if I do the same steps using GUI, the subsetted image is aligning correctly in GIS.

As I have to subset more than 100 images, I would be grateful if any one of you could suggest what I am doing wrong here.

#2

Just a follow-up on my above post. It seems like the Graph Builder image didn’t upload correctly.
The following a copy of the Graph Builder image I used:

Graph_builder
Graph_builder.jpg2256×273 55.5 KB

#3

Could you make the subset as the first operator after Read, and then check up the results,

#4

As you suggested I have tried to subset the image as the first operator following Read and I have been getting the following error message:

Subset_first%20error
Subset_first error.jpg3711×2727 632 KB

#5

That’s mean the polygon doesn’t intersect with the AOI,

The first option now is to apply all steps manually as test, concerning the step of subset convert the wkt to shpfile, and then use it,

The second option is to make the subset operator after apply orbit, also do this manually,

Please let me now if it helps,

#6

As I posted earlier, if we do it manually through the SNAP GUI it works perfectly.

However, if we try to automate it it through Graph Builder (Read-Apply orbit file- calibration-terrain correction-subset-write) using WKT polygon coordinates, there will be an offset of roughly 200 km to North-West.

I tried five different Sentinel 1 GRD files and none of them align correctly in GIS using the above graph.

#7

I think the crs in degree, ESPG:3426 , is that right?,

#8

WKT polygon coordinates are in WGS84/Geographic (EPSG 4326).

I think SNAP can take WKT in geographic co-ordidnates (Lat/long decimal degrees) .

#9

Actually it seems the operator in GB, couldn’t read also in meter, because I faced up same problem, Hopefully we could get an answer from the developers.

#10

Just come across the following thread which discuss about subsetting issues using WKT/Shape format.