areamat
Surface area covered by nonzero values in binary data grid
Syntax
A = areamat(BW,R)
A = areamat(BW,R,ellipsoid)
[A, cellarea] = areamat(...)
Description
A = areamat(BW,R) returns the surface area covered by the elements of the
binary regular data grid BW, which contain the value 1
(true). BW can be the result of a logical
expression such as BW = (topo60c > 0). R can be
a geographic raster reference object, a referencing vector, or a referencing
matrix.
If R is a geographic raster reference object,
its RasterSize property must be consistent with size(BW) and
its RasterInterpretation must be 'cells'.
If R is a referencing vector, it must be
a 1-by-3 with elements:
[cells/degree northern_latitude_limit western_longitude_limit]
If R is a referencing matrix, it must be
3-by-2 and transform raster row and column indices to or from geographic
coordinates according to:
[lon lat] = [row col 1] * R
If R is a referencing matrix, it must define
a (non-rotational, non-skewed) relationship in which each column of
the data grid falls along a meridian and each row falls along a parallel.
Nearest-neighbor interpolation is used by default. NaN is returned
for points outside the grid limits or for which lat or lon contain
NaN. All angles are in units of degrees.
The output A expresses surface area as a
fraction of the surface area of the unit sphere (4*pi), so the result
ranges from 0 to 1.
A = areamat(BW,R,ellipsoid) calculates the surface area on the ellipsoid
or sphere defined by the input ellipsoid, which can be a referenceSphere, referenceEllipsoid, or oblateSpheroid object, or a vector of the form [semimajor_axis
eccentricity]. The units of the output, A, are the
square of the length units in which the semimajor axis is provided. For example, if
ellipsoid is replaced with
wgs84Ellipsoid('kilometers'), then A is in
square kilometers. If you do not specify ellipsoid and
R is a reference object with a non-empty
GeographicCRS property, then areamat uses
the ellipsoid contained in the Spheroid property of the
geocrs object in the GeographicCRS property of
R.
[A, cellarea] = areamat(...) returns a
vector, cellarea, describing the area covered by
the data cells in BW. Because all the cells in
a given row are exactly the same size, only one value is needed per
row. Therefore cellarea has size M-by-1,
where M = size(BW,1) is the number of rows in BW.
Examples
Tips
Given a regular data grid that is a logical 0-1 matrix, the areamat
function returns the area corresponding to the true, or 1, elements. The input data grid
can be a logical statement, such as (topo60c > 0), which is 1
everywhere that topo60c is greater than 0 meters, and 0 everywhere
else. This is an illustration of that matrix:
This calculation is based on the areaquad function
and is therefore limited only by the granularity of the cellular data.