Multi UTM-zones specification
Goals
Sentinel-2 and Sentinel-3 products can spread over several UTM zones. At the moment only one UTM zone can be specified for the product, having a product over several UTM zones is not supported.
Possible solutions
1. Re-project part of the product.
This would consist in extending the API to specify an UTM zone while opening the product. On the HMI this would mean a new interface to let the user choose the reference UTM zone, on the GPT this would mean an extra option for the UTM zone. Granules on different UTM zones would be reprojected on the main UTM zone. By default the main UTM zone would be selected.
Pros:
- visualisation of the full product in one image
Cons:
- loss of data / modified images due to reproject
- the user wouldn't know what is the reprojected zone potentially transformed from the tiles not transformed
- User might not know which UTM zone to select
2. Open only the tiles which are over a selected UTM zone
As for the solution 1. , the API would be extend to display only tiles that are on a selected UTM zone. By default the main UTM zone would be selected.
Pros:
- No reprojection
- selected UTM zone can be displayed
Cons:
- Only one UTM zone can be displayed at a time
- User might not know which UTM zone to select
3. Open granules which are on different UTM zones on different bands.
This would consist in using the multi-resolution change to assiciate an UTM zone for each granule.
On the SNAP HMI this means having different bands for granules with different UTM zones, and regrouping granules per UTM zones, by example:
\[1\] ProductName
+Metadata
- Bands
- UTM31
UTM31_B1
UTM31_B2
UTM31_B3
UTM31_B4
- UTM32
UTM32_B1
UTM32_B2
UTM32_B3
UTM32_B4
Pros:
- All granules can be visualised
- No reprojection
- No user choice before opening the product
Cons:
- SNAP product model has to be compatible with this
Conclusion
If compatible with the SNAP product model, the last option is prefered.