POLAR - Functions to map data in rectangular coordinates to polar and vise versa

recttopolar	convert a function p(x,y) to a function q(a,r)
polartorect	convert a function q(a,r) to a function p(x,y)

Function Prototypes:
void recttopolar ( int nx, float dx, float fx, int ny, float dy, float fy,
			float **p, int na, float da, float fa, int nr,
			float dr, float fr, float **q);
void polartorect ( int na, float da, float fa, int nr, float dr, float fr,
			float **q, int nx, float dx, float fx, int ny,
			float dy, float fy, float **p)

recttopolar:
Input:
nx		number of x samples
dx		x sampling interval
fx		first x sample
ny		number of y samples
dy		y sampling interval
fy		first y sample
p		array[ny][nx] containing samples of p(x,y)
na		number of a samples
da		a sampling interval
fa		first a sample
nr		number of r samples
dr		r sampling interval
fr		first r sample

Output:
q		array[nr][na] containing samples of q(a,r)

polartorect:
Input:
na		number of a samples
da		a sampling interval
fa		first a sample
nr		number of r samples
dr		r sampling interval
fr		first r sample
nx		number of x samples
dx		x sampling interval
fx		first x sample
ny		number of y samples
dy		y sampling interval
fy		first y sample
q		array[nr][na] containing samples of q(a,r)

Output:
p		array[ny][nx] containing samples of p(x,y)

Notes:
The polar angle a is measured in radians, 
x = r*cos(a) and y = r*sin(a).

recttopolar:
Linear extrapolation is used to determine the value of p(x,y) for
x and y coordinates not in the range corresponding to nx, dx, ....

polartorect:
Linear extrapolation is used to determine the value of q(a,r) for
a and r coordinates not in the range corresponding to na, da, ....

Author:  Dave Hale, Colorado School of Mines, 06/15/90