PCA - georeferenced images

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PCA - georeferenced images

Marijke

 

Dear all,

I want to calculate a PCA on Landsat images. This Landsat images are georeferenced and contain a lot of “0”-values because of the rotation of the original image (which I don’t have).

It look likes the PCA takes this zeros into account to calculate the matrix. Is this true and is there a possibility to avoid this?

Thanks in advance for your help!

Marijke

 

----

Marijke De Ryck

Praktijkassistent

T +32 9/264 46 94         

M +32 474/39.02.86

 

Vakgroep Geografie

 

Campus De Sterre, WE12, Krijgslaan 281, 9000 Gent routebeschrijving

 

www.ugent.be

www.facebook.com/ugent

www.twitter.com/ugent


 

 

 


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Re: PCA - georeferenced images

Bas Retsios
Hello,

Sorry for the late reply, it is summer-break season here.
If you need to "ignore" the 0-values, convert them to "undefined":
The Principal Component Analysis algorithm ignores undefined pixels.

To do this, the following statement must be applied to each of the input bands:
out_band_XX:=iff(in_band_XX.mpr<>0,in_band_XX.mpr,?)
This statement will make a copy of the input band, where 0 has changed to "undefined".

For PCA, the easiest is to execute this statement inside the operation "MapList Calculation". This will automatically apply it to all bands in the maplist that is required for PCA. A copy of the maplist will be created (with a new name, chosen by you), where 0 is changed to "undefined" in all bands.

After you have navigated to the folder with your data, start the "MapList Calculation" operation from the ILWIS menu, and proceed as follows:
1. Reduce the Input MapLists to 1
2. In MapList @1, select the maplist that is to undergo the PCA analysis.
3. In Expression, type the following:
iff(@1<>0,@1,?)
4. Fill in a nice filename in Output MapList
5. Click "Show". This will compute the new maplist.

Now you can use this new maplist as the input of the Principal Component Analysis.

Cheers,

Bas Retsios
ILWIS team

On 24/8/2017 3:39 PM, Marijke De Ryck wrote:

 

Dear all,

I want to calculate a PCA on Landsat images. This Landsat images are georeferenced and contain a lot of “0”-values because of the rotation of the original image (which I don’t have).

It look likes the PCA takes this zeros into account to calculate the matrix. Is this true and is there a possibility to avoid this?

Thanks in advance for your help!

Marijke

 

----

Marijke De Ryck

Praktijkassistent

T +32 9/264 46 94         

M +32 474/39.02.86

 

Vakgroep Geografie

 

Campus De Sterre, WE12, Krijgslaan 281, 9000 Gent routebeschrijving

 

www.ugent.be

www.facebook.com/ugent

www.twitter.com/ugent


 

 

 



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