grid.info: Grid Information from Geographic (lat lon) Projections

In jjvanderwal/SDMTools: Species Distribution Modelling Tools: Tools for processing data associated with species distribution modelling exercises

Description

Since spatial grids in geographic projections do not have equal area or perimeters, grid.info extracts perimeter & area related information for latitudinal bands with differing longitudinal widths.

Outputs lengths are in m using Vincenty's equation (distance)and areas in m2. Surface areas are calculated summing surface areas of spherical polygons as estimated using l'Huiller's formula.

Usage

grid.info(lats, cellsize, r = 6378137)

Arguments

lats	is a vector of latitudes representing the midpoint of grid cells
cellsize	is a single value (assuming square cells) or a two value vector (rectangular cells) representing the height (latitude) and width (longitude) of the cells
r	is a single value representing the radius of the globe in m. Default is for the WGS84 elipsoid

Value

a data.frame listing:

lat	the latitude representing the midpoint of the cell
top	length of the top of the cell (m)
bottom	length of the bottom of the cell (m)
side	length of the side of the cell (m)
diagnal	length of the diagnals of the cell (m)
area	area of the cell (m2)

Author(s)

Jeremy VanDerWal [e-mail]

References

information on l'Huiller's formula http://williams.best.vwh.net/avform.htm for moreinfo) code for estimating area of polygon on sphere was modified from http://forum.worldwindcentral.com/showthread.php?t=20724

Examples

#show output for latitudes from -87.5 to 87.5 at 5 degree intervals
grid.info(lats=seq(-87.5,87.5,5), 5)

jjvanderwal/SDMTools documentation built on May 19, 2019, 11:40 a.m.