Landsat scenes in the southern hemisphere when imported in Idrisi are always in UTM N. USGS says that "The southern UTM Zone projection has been removed to avoid complications with some cartographic products. Although southern hemisphere scenes will incorrectly be tagged as northern hemisphere scenes, the data and coordinates will be accurate and displayed correctly." It is time consuming to re-project scenes to UTM S- Is there a quick fix to this? If the underlying data is accurate it should be sufficient to change the projection in name alone correct? How can I do this?
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6 comments
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Clark Labs Becky,
Only if the underlying data are incorrectly tagged, then no need to reproject. Just change the reference system in Metadata in IDRISI Explorer to the correct one. If you have many files to update, you can use the module METAUPDATE.
James Toledano
Clark Labs
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Becky Dickson Thanks James- Huge time saver!
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Paulo Eduardo Cardoso But changing only reference system from utm-33n to utm-33s do not solve the problem. It's necessary to change Min and Max X and Y. How to deal with this?
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Clark Labs Tech Support Team Dear Paulo,
If an image has been incorrectly geometrically coded, it will need to be corrected in order to be properly projected. However, if it is simply a labeling mistake as with the USGS data, the projection only needs to be redefined. To geometrically correct an image I would suggest using the RESAMPLE module. Please see the help documentation on this module to learn more about its features and uses.
Best Regards,
Andrew Hostetler
Clark Labs Technical Support
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FlorS I know this is a little late but I just got into this problem with Landsat and was checking if someone here had the same issue.
Landsat Reports all the images in UTM N, everything that is UTM south will have negative coordinates meaning that it is south of the equator, The method of correction that I'll describe below only works if the southern hemisphere images are reported in UTM-N and the Y values are negatives.
In UTM-N the equator has a value of 0 so everything hat has negative Y coordinates represent southern hemisphere images.
In UTM-S the equator has a value of 10,000,000.
To convert your min and max values then you have to update your max Y and Min Y in your metadata.
New max Y = 10,000,000 - old Max Y
New min Y = 10,000,000 - old Min Y
So for example if your original image had values of
min. X : 641385.0000000
max. X : 873915.0000000
min. Y : -262815.0000000
max. Y : -55785.0000000
Your new image will be
min. X : 641385.0000000
max. X : 873915.0000000
min. Y : 9737185
max. Y : 9944215
You also need to change the projection to UTM - S in the metadata.
You can use METAUPDATE if you need to change multiple bands!!
I hope this helps!
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Clark Labs Flor is absolutely correct. All Landsat Level-1 products are documented as UTM North with a false northing of 0, regardless if they are North or South. As a result, you can not simply reproject a Landsat Level-1 scene that is documented as UTM North but is really in UTM South. If you have an image that is in UTM South but by default imported as UTM North, only in the case of Landsat Level-1 data, follow Flor's steps above, i.e., in Metadata:
1. Add 10,000,000 to each the Y minimum and maximum values,
2. Change the Projection to the appropriate UTM South zone.
More here:
https://landsat.usgs.gov/why-do-southern-hemisphere-scenes-not-display-correct-utm-designation
James
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