# Ngl.gc_qarea

Finds the area of a convex quadrilateral patch on a sphere whose vertices are given in degrees as lat/lon pairs.

## Prototype

area = Ngl.gc_qarea(lat1, lon1, lat2, lon2, lat3, lon3, lat4, lon4, radius=1.)

## Arguments

*lat1*,

*lon1*

Latitude and longitude, in degrees, of the first vertex. These can be scalars, lists, or NumPy arrays.

*lat2*,

*lon2*

Latitude and longitude, in degrees, of the second vertex. These can be scalars, lists, or NumPy arrays.

*lat3*,

*lon3*

Latitude and longitude, in degrees, of the third vertex. These can be scalars, lists, or NumPy arrays.

*lat4*,

*lon4*

Latitude and longitude, in degrees, of the fourth vertex. These can be scalars, lists, or NumPy arrays.

*radius=1.*

An optional argument specifying the radius of the sphere.

## Return value

*area*

The desired spherical area which is a scalar if the arguments are scalars, or a NumPy array of the same size as the input arrays otherwise. The vertices must be entered in either clockwise or counter-clockwise order. A returned area is that bounded by arcs of great circles connecting the vertices.

## Description

This function finds the area of a *convex* quadrilateral patch on
a sphere
whose vertices are given in degrees as lat/lon pairs and *are
listed in either clockwise or counter-clockwise order*. The area
found is that area bounded by great circle arcs connecting the vertices.
The algorithm simply calls **Ngl.gc_tarea**
on two triangles.

## See Also

**Ngl.gc_convert**,
**Ngl.gc_dist**,
**Ngl.gc_inout**,
**Ngl.gc_interp**,
**Ngl.gc_qarea**,
**Ngl.gc_tarea**

## Examples

The following:

# # Find an area of a half-lune that is 1/20th the area of a unit # sphere (4*pi/20). # import Ngl, math pi = 4.*math.atan(1.) area = Ngl.gc_qarea(-90., 0., 0., 18., 0., 0., 0., -18.) print "%9.7f %9.7f" % (area, 4*pi/20.) Ngl.end()produces:

0.6283185 0.6283185