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 Last Post 13 Dec 2017 05:10 AM by  Bisma Qazi Linear Spectral Unmixing (LSU)  2 Replies Sort: Oldest First Most Recent First
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Bisma Qazi

New Member

Posts:16

 25 Oct 2017 11:26 AM Hi, How do we decide the weight in case of LSU ? I am getting values >1 and < 0 in the output images even after applying the sum constraint and setting the weight to default value (1)

MariM

Veteran Member

Posts:2396

 26 Oct 2017 07:05 AM The help for LSU states: You pick a weight factor (the default value is 1) for the extra constraint equation. This weighted unit-sum constraint is then added to the system of simultaneous equations in the unmixing inversion process. Larger weights in relation to the variance of the data cause the unmixing to honor the unit-sum constraint more closely. To strictly honor the constraint, the weight should be many times the spectral variance of the data. For example, If you use a weight of 100 with data that range from 0 to 1, it'll be a "heavy" weight and the fractions will be near unit sum. The same weight of 100 for data that range from 0 to10000, will be a very "light" weight, and this extra equation will have almost no effect. To get the same effect you'd need weight to be 1000000. It's the ratio that matters not the size of weight alone. You might also consider why it may be misleading to use constraints: http://www.harrisgeospati...leID/19704/1630.aspx

Bisma Qazi

New Member

Posts:16

 13 Dec 2017 05:10 AM So if my data varies between 0-100, shall I use the weight factor of 10000 to apply the constraint?
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