Messages from Usenet group comp.lang.idl-pvwave, compiled by Paulo Penteado
Re: MPFIT2DFUN- use for a time series of images?
On Mar 10, 3:01 pm, Katie <kmwhite21...@gmail.com> wrote: > I want to fit pixel values to a logistic model that each have X, Y > coordinates and a day of the year value associated with them. I see > from the MPFIT2DFUN documentation how to define X, Y for a each Z > dependent value and the dependent error value, but can a third > variable (day of the year in this case) be defined in order to fit a > curve in MPFIT2DFUN? I currently have each each date as a separate > band in a stacked image file that I exported as an ASCII file. I want > to determine the day of the year that the pixel values (vegetation > indices) reach a value on the the curve. > > Any suggestions, or perhaps I am not understanding the MPFIT2DFUN > correctly (I am very new to IDL)? Well, you're trying to fit 3d data with a 2d function. I would look at mpfitfun or just mpfit.
On Mar 10, 9:01 pm, Katie <kmwhite21...@gmail.com> wrote: > I want to fit pixel values to a logistic model that each have X, Y > coordinates and a day of the year value associated with them. I see > from the MPFIT2DFUN documentation how to define X, Y for a each Z > dependent value and the dependent error value, but can a third > variable (day of the year in this case) be defined in order to fit a > curve in MPFIT2DFUN? I currently have each each date as a separate > band in a stacked image file that I exported as an ASCII file. I want > to determine the day of the year that the pixel values (vegetation > indices) reach a value on the the curve. > > Any suggestions, or perhaps I am not understanding the MPFIT2DFUN > correctly (I am very new to IDL)? Katie, You will need to iterate over the rows and columns of your image and fit the logistic model to the time-series at each row/column value. Indeed, MPFITFUN is one of the tools to do that. A couple of years ago I implemented this approach for use with the GIMMS dataset. In fact it uses a double logistic model to model the NDVI time-series. My implementation does not include a variable day-of-year (just regular time-steps) but this is a trivial extension. It also uses IDLs native Curve_Fit routine rather then MPFITFUN, although the latter is better. If you're interested I can send you a copy of that code. Allard
On Mar 11, 7:49 am, Allard de Wit <ajwde...@xs4all.nl> wrote: > On Mar 10, 9:01 pm, Katie <kmwhite21...@gmail.com> wrote: > >> I want to fit pixel values to a logistic model that each have X, Y >> coordinates and a day of the year value associated with them. I see >> from the MPFIT2DFUN documentation how to define X, Y for a each Z >> dependent value and the dependent error value, but can a third >> variable (day of the year in this case) be defined in order to fit a >> curve in MPFIT2DFUN? I currently have each each date as a separate >> band in a stacked image file that I exported as an ASCII file. I want >> to determine the day of the year that the pixel values (vegetation >> indices) reach a value on the the curve. > >> Any suggestions, or perhaps I am not understanding the MPFIT2DFUN >> correctly (I am very new to IDL)? > > Katie, > > You will need to iterate over the rows and columns of your image and > fit > the logistic model to the time-series at each row/column value. > Indeed, MPFITFUN is one of the tools to do that. > > A couple of years ago I implemented this approach for use with the > GIMMS > dataset. In fact it uses a double logistic model to model the NDVI > time-series. My implementation does not include a variable day-of-year > (just regular time-steps) but this is a trivial extension. It also > uses IDLs native Curve_Fit routine rather then MPFITFUN, although the > latter is better. > > If you're interested I can send you a copy of that code. > > Allard Thanks Gray and Allard, that makes more sense, I will look at MPFITFUN-- and yes Allard it would be extremely helpful to be able to look at the copy of your code! Katie
>> Allard > > Thanks Gray and Allard, that makes more sense, I will look at > MPFITFUN-- and yes Allard it would be extremely helpful to be able to > look at the copy of your code! > > Katie Katie, I have put a package on our public ftp server: ftp://sc:Image188@ftp.alterra.nl/pub/adewit/idlsigmoid.zip It contains the following files: fit_phenology_gimms.pro - a wrapper I used to run it over GIMMS (needs ENVI) fit_sigmoid.pro - a wrapper for sigmoid fitting fsigmoid.pro - double sigmoid defined as a function psigmoid.pro - double sigmoid defined as a procedure test_fit_sigmoid_curvefit.pro - curve fitting using curvefit test_fit_sigmoid_mpfit.pro - curve fitting using mpfitfun Some test profiles, needed by the test* routines test_ndvi_zprofile2.sav test_ndvi_zprofile3.sav test_ndvi_zprofile4.sav test_ndvi_zprofile5.sav Cheers Allard
On Monday, March 14, 2011 9:46:22 PM UTC+8, Allard de Wit wrote: >>> Allard >> >> Thanks Gray and Allard, that makes more sense, I will look at >> MPFITFUN-- and yes Allard it would be extremely helpful to be able to >> look at the copy of your code! >> >> Katie > > Katie, > > I have put a package on our public ftp server: > ftp://sc:Image188@ftp.alterra.nl/pub/adewit/idlsigmoid.zip > > It contains the following files: > fit_phenology_gimms.pro - a wrapper I used to run it over GIMMS (needs > ENVI) > fit_sigmoid.pro - a wrapper for sigmoid fitting > fsigmoid.pro - double sigmoid defined as a function > psigmoid.pro - double sigmoid defined as a procedure > test_fit_sigmoid_curvefit.pro - curve fitting using curvefit > test_fit_sigmoid_mpfit.pro - curve fitting using mpfitfun > > Some test profiles, needed by the test* routines > test_ndvi_zprofile2.sav > test_ndvi_zprofile3.sav > test_ndvi_zprofile4.sav > test_ndvi_zprofile5.sav > > Cheers > > Allard Dear Allard, I need your codes for curve fitting. Currently I can not download it. I also need your suggestion about my work. I want to extract pheno-pauses from NDVI time-series. I after fitting curve, I need to extract time of phenology according to a fixed NDVI values that is different for every pixel. Need your suggestions guys. New to IDL also, Regards Sawaid