The gapfraction package implements a new barycentric interpolation spike-free canopy height model (CHM) algorithm based on Khosravipour et al. (2013)1 and (2016)2, in addition to two new LiDAR metrics of canopy gap fraction (\(P_o\)), several individual tree crown (ITC) detection algorithms, canopy distance and direction metrics, effective leaf area index (\(L_e\)) and apparent clumping index (\(ACI\)) estimation methods. Four mathematical fisheye (hemispherical) lens models are implemented: equi-angular, equi-distant, stereographic, and orthographic. Finally, a new radial.grid function is included for polar plots, while a modified sun path plotting function is also provided. An alphabetical list of functions contained in the gapfraction package is provided below.
chm - Simple canopy height modelchm.sf - Barycentric interpolation spike-free canopy height modeldd.canopy - Euclidean distance and direction to nearest canopy pixel from plot centerdd.crown - Euclidean distance and direction to nearest tree crown from plot centersitc.mw - Variable-window individual tree crown detectionitc.mw.h - Hierarchical variable-window individual tree crown detectionitc.wat - Watershed segmentation individual tree crown detectionitc.wat.h - Hierarchical watershed segmentation individual tree crown detectionLe.bl - Ground-to-total-return ratio with a spherical leaf angle distributionLe.n - Contact frequency and vertical canopy cover-based effective LAIradial.grid.hemi - Modified radial.grid function supporting hemispherical lens geometriesP.hv - Hemipsherical Voronoi canopy gap fractionP.hv.par - Parallel hemispherical Voronoi canopy gap fraction with SOCKSP.pdn - Point-density-normalized canopy gap fraction, effective LAI (Le), and ACIsun.path - Modified solar position plots of Thomas Steinervcc.aci - Above-height cover index of vertical canopy covervcc.bl - Beer-Lambert-Law-modified intensity-return ratio of vertical canopy covervcc.cv - 2-D Cartesian Voronoi vertical canopy covervcc.fci - First-echo cover index of vertical canopy covervcc.fr - Canopy-to-first-return ration of vertical canopy covervcc.ir - Intesity-return ratio of vertical canopy covervcc.p - Canopy-to-total-pixel ratio of vertical canopy covervcc.r - Canopy-to-total-return ratio of vertical canopy covervcc.sci - Solberg’s cover index of vertical canopy coverKhosravipour et al. (2013) Development of an algorithm to generate a LiDAR pit-free canopy height model. http://www.riegl.com/uploads/tx_pxpriegldownloads/khosravipour_SilviLaser2013.pdf↩
Khosravipour et al. (2016) Generating spike-free digital surface models using LiDAR raw point clouds: A new approach for forestry applications. http://www.sciencedirect.com/science/article/pii/S0303243416300873↩