gapfrac_fisheye {hemispheR}

Derive angular gap fraction from a classified fisheye image

Description

The function calculates the gap fraction for a number of zenith annuli (rings) and azimuth sectors (segments). A list of lens is available for correcting for lens distorsion. Type 'list.lenses'.

Usage

gapfrac_fisheye(
  img.bw,
  maxVZA = 90,
  lens = "equidistant",
  startVZA = 0,
  endVZA = 70,
  nrings = 7,
  nseg = 8,
  message = FALSE,
  display = FALSE
)

Arguments

img.bw

SpatLayer. A binary, single-layer fisheye image generated from binarize_fisheye().

maxVZA

Numeric. The maximum Zenith angle (in degrees) corresponding to the image radius. Default= 90.

lens

Character. The lens type for fisheye-lens correction. A list of lenses is available by typing list.lenses. If missing, it is assumed equidistant.

startVZA

Numeric. The minimum Zenith angle (in degrees) considered in the analysis. Default is 0.

endVZA

Numeric. The maximum Zenith angle (in degrees) considered in the analysis. Default is 70.

nrings

Numeric. The number of equiangular zenith rings considered in the analysis. Default is 7.

nseg

Numeric. The number of azimuth segments considered in the analysis. Default is 8.

message

Logical. If set to TRUE, it reports the circular mask used in the analysis.

display

Logical. If set to TRUE, it desplays the zenith rings and azimuth segments overlaid on the fisheye image.

Value

A dataframe of gap fraction (GF) for zenith rings (rows) and azimuth segments (columns).

Author(s)

Francesco Chianucci

See Also

Lens correction functions have been retrieved from the following sources:

Pekin and Macfarlane 2009: doi:10.3390/rs1041298

Paul Bourke:http://www.paulbourke.net/dome/fisheyecorrect/

Hemisfer: https://www.schleppi.ch/patrick/hemisfer/index.php

Examples

c.im<-system.file('extdata/circular_coolpix4500+FC-E8_chestnut.jpg',package='hemispheR')

#List of lenses for fisheye projection correction:
list.lenses

#Zenith rings similar to LAI-2000/2200:
c.im |>
 import_fisheye(circ.mask=camera_fisheye('Coolpix4500+FC-E8')) |>
  binarize_fisheye() |>
  gapfrac_fisheye(lens='FC-E8',nrings=5,nseg=8,endVZA=75,display=TRUE)

#The hinge angle method close to 1 radian (57):
c.im |>
 import_fisheye(circ.mask=camera_fisheye('Coolpix4500+FC-E8')) |>
  binarize_fisheye() |>
  gapfrac_fisheye(lens='FC-E8',nrings=1,nseg=8,startVZA=55,endVZA=60,display=TRUE)