rcaiman (version 1.2.2)

extract_sky_points_simple: Extract sky points

Description

Extract sky points for model fitting

Usage

extract_sky_points_simple(r, z, a)

Value

An object of the class data.frame with two columns named col and row.

Arguments

r

SpatRaster. A normalized greyscale image. Typically, the blue channel extracted from a canopy photograph. Please see read_caim() and normalize().

z

SpatRaster built with zenith_image().

a

SpatRaster built with azimuth_image().

Details

This function will automatically sample sky pixels following this simple strategy:

• mask out the region of r above 15 and below 75 degrees of zenith angle,

• divide the hemisphere into sectors of 15 degrees each (see sectors_segmentation()),

• search for the maximum digital value in each sector (n = 24),

• divide the hemisphere into rings of 5 degrees each (see rings_segmentation(),

• search for the maximum digital value in each ring (n = 12)

• combine these local maxima (n = 36).

See Also

Other Tool Functions: colorfulness(), correct_vignetting(), defuzzify(), extract_dn(), extract_feature(), extract_rl(), extract_sky_points(), extract_sun_coord(), find_sky_pixels_nonnull(), find_sky_pixels(), masking(), optim_normalize(), percentage_of_clipped_highlights(), read_bin(), read_caim_raw(), read_caim(), write_bin(), write_caim()

Examples

if (FALSE) {
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$Blue)
sky_points <- extract_sky_points_simple(r, z, a)
plot(r)
points(sky_points$col, nrow(caim) - sky_points$row, col = 2, pch = 10)
}