Hi Kimi, The components are given as directions (eigenvectors) and are therefore normalized (unit vectors). You can use the eigenvalues (the variance of each direction) to select the components[1]. They are stored in a file which has the same name as the model but with a .txt extension.
Best wishes, Jordi [1] https://en.wikipedia.org/wiki/Principal_component_analysis#Intuition On Wed 22-Aug-2018 at 15:47:54 +02, Kimi <[email protected]> wrote: > Hi all, > > I would like to do the pca (principal component analysis) of my Sentinel-2 > multiband image composed of nine 20m-L2A rasters. I tried with the > otbcli_DimensionalityReduction module (the method parameter was set to > “pca”), but the statistics of the output image is not as I expected. > Namely, all the bands of the output image has the standard deviation equal to > 1. > > Generally, I expected that the output pca bands have standard deviations > different from 1. This would then allow me to select the most significant > bands according to the variance loss criteria. > > Is this a bug of the DimensionalityReduction –pca algorithm, or there is > maybe another way in orfeo toolbox to get the pca bands without std > normalized to 1? > > Thank you in advance for your time and the help! > > Cheers, > > Kimi > > PS. > > I am using orfeo 6.4.0 from the command line, and there is my code: > >>>otbcli_DimensionalityReduction -in test2.tif -out pca_norOFF.tif -method pca >>>-normalize 0 > >>>otbcli_ComputeImagesStatistics -il pca_norOFF.tif > > and this is the statistics for 9 bands from the pca output image: > > Mean: 2.14067, -1.29191, 0.554654, 0.996805, -0.267422, 0.423317, 0.285117, > 0.281447, -0.183358 Standard Deviation: [1, 1, 1, 1, 1, 1, 1, 1, 1] > > My input multiband image can be downloaded from here: > > https://files.fm/u/2vh7aqvu > > -- -- -- Check the OTB FAQ at http://www.orfeo-toolbox.org/FAQ.html You received this message because you are subscribed to the Google Groups "otb-users" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/otb-users?hl=en --- You received this message because you are subscribed to the Google Groups "otb-users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
