grid.info: 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:
latthe latitude representing
the midpoint of the cell
toplength of the top of
the cell (m)
bottomlength of the bottom of the
cell (m)
sidelength of the side of the cell (m)
diagnallength of the diagnals of the cell (m)
areaarea of the cell (m2)
References
information on l'Huiller's formula
http://williams.best.vwh.net/avform.htm for more
info) code for estimating area of polygon on sphere was
modified from
http://forum.worldwindcentral.com/showthread.php?t=20724