Shadow casting for an elevation data grid

1. A computer-implemented method for creating a shadow mask representing irradiation of a physical scene based upon a plurality of elevation grid points of an array of elevation data associated with the physical scene, the method comprising:

a. receiving elevation point data in which an elevation value is associated with each of a plurality of spatial coordinates;

b. determining, for a specified anchor point, a direction to a light source characterized by an irradiance value at each elevation grid point;

c. associating with the light source a quadrant of an azimuthal circle;

d. selecting a shadow frontline propagation mode based on the quadrant associated with the light source;

e. propagating a shadow horizon along the array of elevation data by projection onto successive lines of elevation data;

f. recursively updating the shadow horizon stored in a frontline buffer of computer memory; and

g. generating a binary shadow mask based on whether a specified elevation point lies above or below the shadow horizon.

2. A computer-implemented method according to claim 1 , further comprising calculating an irradiance contribution to a total insolation incident upon a specified grid point based on the irradiance of the light source at the elevation grid point as modulated by the binary shadow mask.

3. A computer-implemented method according to claim 1 , wherein the light source is the Sun.

4. A computer-implemented method according to claim 1 , wherein propagating a shadow horizon further comprises applying a transformation to the direction of the light source to reflect curvature of an underlying surface of the physical scene.

5. A computer implemented method according to claim 4 , wherein the underlying surface of the physical scene is substantially spherical.

6. A computer-implemented method according to claim 4 , wherein the underlying surface is of the physical scene is the Earth.

7. A computer program product for use of a computer system for generating a shadow mask representing irradiation of a physical scene based upon a plurality of elevation grid points of an array of elevation data associated with the physical scene, the computer program product comprising a non-transitory computer-readable medium on which are stored computer instructions such that, when executed by a processor, the instructions cause the processor to:

a. receive elevation point data in which an elevation value is associated with each of a plurality of spatial coordinates;

b. determine, for a specified anchor point, a direction to a light source characterized by a direction and an irradiance value at each elevation grid point;

c. associate with the light source a quadrant of an azimuthal circle;

d. select a shadow frontline propagation mode based on the quadrant associated with the light source;

e. propagate a shadow horizon along the array of elevation data by projection onto successive lines of elevation data;

f. recursively update the shadow horizon stored in a frontline buffer; and

g. generate a binary shadow mask based on whether a specified elevation point lies above or below the shadow horizon.

8. A computer program product according to claim 7 , wherein the instructions further cause the processor to calculate an irradiance contribution to a total insolation incident upon a specified grid point based on the irradiance of the light source at the elevation grid point as modulated by the binary shadow mask.

9. A computer program product according to claim 7 , wherein the instructions further cause the processor to apply a transformation to the direction of the light source to reflect curvature of an underlying surface of the physical scene.