On Mon 03-Sep-2018 at 14:45:37 +02, Kimi <miluti...@gmail.com> wrote: > Hi Jordi, > > Thank you for your answer and the wiki link! I read carefully the wiki > section, and this is all fine, but I do not know how to interpret the output > image of the “otbcli_DimensionalityReduction”. > > Is the output image the pca-transformed input image? If yes, why is the > standard deviation of each band in the output image equal to 1?
The outputs are the components. They have unit variance, and if you wan to reconstruct the original data, you have to multiply each component by the square root of the correspondign eigenvalue. > > You also mentioned the following “You can use the eigenvalues … They are > stored in a file > which has the same name as the model but with a .txt extension. ”. > > Maybe I am missing something here, but in “otbcli_DimensionalityReduction” > there is no “model” parameter. The only txt file I can get is a 9x9 matrix > resulting from the option “-outmatrix”. However, in the otb help, it is > explained shortly that this is a “transformation matrix”. > > Does the “-outmatrix” option provide a matrix with the eigenvectors? Sorry. I thought you were using the new dimensionality reduction applications (TrainDimensionalityReduction and ImageDimensionalityReduction). The former has a -io.out parameter to store the reduction model. In the case of the application you are using, I guess that the transformation matrix must contain non unit eigenvectors from which you can derive the eigenvalues (but I am only guessing, you should check). > > Thank you for your time and help! > > Cheers, > > Kimi > > On Monday, 3 September 2018 11:46:43 UTC+2, jordi.inglada wrote: > > 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 > > -- -- -- 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 otb-users@googlegroups.com To unsubscribe from this group, send email to otb-users+unsubscr...@googlegroups.com 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 otb-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
