libpysal.cg.linear2arcdist¶

libpysal.cg.linear2arcdist(linear_dist, radius=6371.0)[source]¶

Convert a linear distance in the unit sphere (R3) to an arc distance based on supplied radius.

Parameters:¶

linear_dist : float¶

The linear distance to convert.

radius : float¶

The radius of a sphere. Default is Earth’s radius in kilometers, RADIUS_EARTH_KM (6371.0). Earth’s radius in miles, RADIUS_EARTH_MILES (3958.76) is also an option. Source: http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html

Returns:¶

arc_dist – The arc distance conversion of linear_dist.

Return type:¶

float

Raises:¶

ValueError – Raised when linear_dist exceeds the diameter of the unit sphere.

Examples

>>> pt0 = (0, 0)
>>> pt1 = (180, 0)
>>> d = arcdist(pt0, pt1, RADIUS_EARTH_MILES)
>>> d == linear2arcdist(2.0, radius=RADIUS_EARTH_MILES)
True