grid.info {SDMTools}R Documentation

Grid Information from Geographic (lat lon) Projections

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 jjvanderwal@gmail.com

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)

[Package SDMTools version 1.1-221 Index]