R/find.intersect.R

In VennDiagram: Generate High-Resolution Venn and Euler Plots

# The VennDiagram package is copyright (c) 2012 Ontario Institute for Cancer Research (OICR)
# This package and its accompanying libraries is free software; you can redistribute it and/or modify it under the terms of the GPL
# (either version 1, or at your option, any later version) or the Artistic License 2.0.  Refer to LICENSE for the full license text.
# OICR makes no representations whatsoever as to the SOFTWARE contained herein.  It is experimental in nature and is provided WITHOUT
# WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE OR ANY OTHER WARRANTY, EXPRESS OR IMPLIED. OICR MAKES NO REPRESENTATION
# OR WARRANTY THAT THE USE OF THIS SOFTWARE WILL NOT INFRINGE ANY PATENT OR OTHER PROPRIETARY RIGHT.
# By downloading this SOFTWARE, your Institution hereby indemnifies OICR against any loss, claim, damage or liability, of whatsoever kind or
# nature, which may arise from your Institution's respective use, handling or storage of the SOFTWARE.
# If publications result from research using this SOFTWARE, we ask that the Ontario Institute for Cancer Research be acknowledged and/or
# credit be given to OICR scientists, as scientifically appropriate.

# find the intersection of two circles
find.intersect <- function(d, r1, r2) {

	beta  <- (r1^2 + d^2 - r2^2) / (2 * r1 * d);
	gamma <- (r2^2 + d^2 - r1^2) / (2 * r2 * d);

	area <- r1^2 * (acos(beta) - 0.5 * sin(2 * acos(beta))) + r2^2 * (acos(gamma) - 0.5 * sin(2 * acos(gamma)));
	return(area);
	}