{ RCSid $Id: fisheye_corr.cal,v 1.1 2016/08/01 00:08:38 greg Exp $ }
{
	Correct fisheye image using a distortion function:

		rad(r) =	function of r in [0,.5] range, returing same

	This function takes the pixel distance from the image center, where
	1.0 is the full width of the image constituting 180-degrees of view.
	The output is the corrected distance from the center for the output.

	pcomb -e 'rad(r)=my_function(r)' -f fisheye_corr.cal \
		-o fisheye.hdr > corrected.hdr

	We also clear the region outside the r=[0,.5] circle to black.

	Note that you will need to add back the VIEW= line to the header, e.g.:

		echo "VIEW= -vta -vh 180 -vv 180" > corrected.hdr
		(above_command) >> corrected.hdr
}
xc : xres/2;
yc : yres/2;
sq(x) : x*x;
r = sqrt(sq((x-xc)/xres) + sq((y-yc)/yres));
mapped_r = rad(r);
{ If your mapping goes the other way, invert the multiplier with:
	rmult = r/(mapped_r+1e-7);
}
rmult = mapped_r/(r+1e-7);
xoff = (x-xc)*(1-rmult);
yoff = (y-yc)*(1-rmult);
ro=if(.5-mapped_r, ri(1,xoff,yoff), 0);
go=if(.5-mapped_r, gi(1,xoff,yoff), 0);
bo=if(.5-mapped_r, bi(1,xoff,yoff), 0);