R: Grid Information from Geographic (lat lon) Projections

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 1.1-221.2 Index]