r2dRue (version 1.0.3)

regStepRaster: Stepwise regression over raster images

Description

This function performs a stepwise regression with two predictors. The regression is made in standard form, therefore the reported regression coefficients are in standard deviation units. Multiple regression is accepted only if the second variable produces a significant increment of determination. Else, single correlations are explored and correlation coefficients are reported if significant. Significance is set to p

Usage

regStepRaster(ndviFl, timeFl, aridFl, outFl, silent = FALSE, ...)

Arguments

ndviFl

Raster group with the file names of the annual Vegetation Index rasters.

timeFl

Raster group with the file names of the annual year number-order rasters.

aridFl

Raster group with the file names of the annual Aridity Index rasters.

outFl

A list of 7 file names to save the results.

silent

Logical. If TRUE, comment and non-fatal CPL driver errors are suppressed.

...

Any unmatched parameter will be passed to the writeGDAL routine. Usually drivername=..., or mvFlag=...

Value

• Returns no value, but saves to disk the following raster files. They belong to the SpatialGridDataFrame class
• index
  individual label for each grid cell
• effect_time
  rate of change in std.dev. of vegetation index per one std.dev. of time; zero if non significant
• effect_arid
  rate of change in std.dev. of vegetation index per one std.dev. of aridity; zero if non significant
• veg_response
  significant response of vegetation index to time (1), aridity (2), both (3) or none (4)
• ta_single
  single correlation coefficient of time and aridity; zero if non significant
• tv_single
  single correlation coefficient of time and vegetation index; zero if non significant
• av_single
  single correlation coefficient of aridity and vegetation index; zero if non significant
• viMeyyyy
  mean annual vegetation index corresponding to year yyyy
• aiMeyyyy
  mean annual aridity index corresponding to year yyyy
• timeyyyy
  dummy raster containing year yyyy in each grid cell

Details

The rasters specified in argument timeFL are dummy images with the year number-order, or simply the year, in each grid cell. This is used as one of the predictors. The rationale is explained in del Barrio et al. below. The regression procedure has been taken from Box 9.1 of Sokal below.

References

del Barrio, G., Puigdefabregas, J. Sanjuan, M.E., Stellmes, M. & Ruiz, A. (2010). Assessment and monitoring of land condition in the Iberian Peninsula, 1989-2000. Remote Sensing of Environment, 114: 1817-1832 http://dx.doi.org/10.1016/j.rse.2010.03.009 Sokal, R. R., & Rohlf, F. J. (1995). Biometry. New York: W.H. Freeman and Co.

See Also

rgf.create