fit_coneshaped_model {rcaiman}

Fit cone-shaped model

Description

Statistical modeling for predicting digital numbers from spherical coordinates.

Usage

fit_coneshaped_model(sky_points, use_azimuth_angle = TRUE)

Arguments

sky_points

The data.frame returned by extract_rl() or a data.frame with same structure and names.

use_azimuth_angle

Logical vector of length one. If TRUE, the Equation 4 from Díaz and Lencinas (2018)) is used: sDN = a + b \cdot \theta + c \cdot \theta^2 + d \cdot sin(\phi) + e \cdot cos(\phi), where sDN is sky digital number, a,b,c,d and e are coefficients, \theta is zenith angle, and \phi is azimuth angle. If FALSE, the next simplified version based on Wagner (2001) is used: sDN = a + b \cdot \theta + c \cdot \theta^2.

Details

This method was presented in Díaz and Lencinas (2018), under the heading Estimation of the sky DN as a previous step for our method. If you use this function in your research, please cite that paper in addition to this package (⁠citation("rcaiman"⁠).

Value

A list of two objects, one of class function and the other of class lm (see stats::lm()). If the fitting fails, it returns NULL. The function requires two arguments–zenith and azimuth in degrees–to return relative luminance.

References

Díaz GM, Lencinas JD (2018). “Model-based local thresholding for canopy hemispherical photography.” Canadian Journal of Forest Research, 48(10), 1204–1216. doi:10.1139/cjfr-2018-0006.

Wagner S (2001). “Relative radiance measurements and zenith angle dependent segmentation in hemispherical photography.” Agricultural and Forest Meteorology, 107(2), 103–115. doi:10.1016/s0168-1923(00)00232-x.

See Also

thr_mblt()

Other Sky Reconstruction Functions: cie_sky_model_raster(), fit_cie_sky_model(), fit_trend_surface(), fix_reconstructed_sky(), interpolate_sky_points(), ootb_sky_reconstruction()

Examples

## Not run: 
path <- system.file("external/DSCN4500.JPG", package = "rcaiman")
caim <- read_caim(path, c(1250, 1020) - 745, 745 * 2, 745 * 2)
z <- zenith_image(ncol(caim), lens("Nikon_FCE9"))
a <- azimuth_image(z)
r <- gbc(caim$Blue)

sky_points <- extract_rl(r, z, a, extract_sky_points_simple(r, z, a),
                         NULL,
                         use_window = FALSE)#this is important when
                                            #extract_sky_points_simple()
                                            #is used
model <- fit_coneshaped_model(sky_points$sky_points)
summary(model$model)
sky_cs <- model$fun(z, a)
plot(r/sky_cs)
plot(sky_cs)

z <- zenith_image(50, lens())
a <- azimuth_image(z)
sky_cs <- model$fun(z, a)
persp(sky_cs, theta = 90, phi = 20)

## End(Not run)