From b6cb0b189243bac7718cb4ddc65630a971ddfbeb Mon Sep 17 00:00:00 2001
From: Arun Isaac
Date: Tue, 16 Mar 2021 13:23:13 +0530
Subject: Implement simplified cone sampling algorithm.
* src/nd-random.sc (hollow-cone-random-vector): Implement simplified
algorithm that directly samples the surface of the sphere instead of
sampling a disk and projecting it onto the surface.
---
src/nd-random.sc | 17 ++++++++---------
1 file changed, 8 insertions(+), 9 deletions(-)
(limited to 'src')
diff --git a/src/nd-random.sc b/src/nd-random.sc
index 02ad997..a9b08b3 100644
--- a/src/nd-random.sc
+++ b/src/nd-random.sc
@@ -98,16 +98,15 @@ dx. THETA should be in [0,pi]."
(define (hollow-cone-random-vector r mean theta-min theta-max x)
(void (const gsl-rng*) (const gsl-vector*) double double gsl-vector*)
;; Generate random vector around the nth canonical basis vector.
- (let* ((n size-t (: x size)))
+ (let* ((n size-t (: x size))
+ (theta double (solid-angle->planar-angle
+ (gsl-ran-flat r
+ (planar-angle->solid-angle theta-min n)
+ (planar-angle->solid-angle theta-max n))
+ n)))
(gsl-ran-dir-nd r (- n 1) (: x data))
- (gsl-vector-scale x (* (cos theta-max)
- (tan (solid-angle->planar-angle
- (gsl-ran-flat r
- (planar-angle->solid-angle theta-min n)
- (planar-angle->solid-angle theta-max n))
- n))))
- (gsl-vector-set x (- n 1) (cos theta-max)))
- (gsl-vector-scale x (/ 1 (gsl-blas-dnrm2 x)))
+ (gsl-vector-scale x (sin theta))
+ (gsl-vector-set x (- n 1) (cos theta)))
;; Rotate to arbitrary basis.
(rotate-from-nth-canonical x mean))
--
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