--- ray/doc/ray.1	2017/04/08 00:09:35	1.31
+++ ray/doc/ray.1	2023/05/11 17:18:39	1.39
@@ -1,8 +1,8 @@
-.\" RCSid "$Id: ray.1,v 1.31 2017/04/08 00:09:35 greg Exp $"
+.\" RCSid "$Id: ray.1,v 1.39 2023/05/11 17:18:39 greg Exp $"
 .\" Print using the -ms macro package
-.DA 07/10/2016
+.DA 5/11/2023
 .LP
-.tl """Copyright \(co 2016 Regents, University of California
+.tl """Copyright \(co 2023 Regents, University of California
 .sp 2
 .TL
 The
@@ -630,6 +630,8 @@ arguments have additional flexibility to specify the s
 Also, rather than roughness, specular power is used, which has no
 physical meaning other than larger numbers are equivalent to a smoother
 surface.
+Unlike other material types, total reflectance is the sum of
+diffuse and specular colors, and should be adjusted accordingly.
 .DS
 mod ashik2 id
 4+ ux uy uz funcfile transform
@@ -947,6 +949,30 @@ invisible from behind.
 Unlike other data-driven material types, the BSDF type is fully
 supported and all parts of the distribution are properly sampled.
 .LP
+.UL aBSDF
+.PP
+The aBSDF material is identical to the BSDF type with two important
+differences.
+First, proxy geometry is not supported, so there is no thickness parameter.
+Second, an aBSDF is assumed to have some specular through component
+(the 'a' stands for "aperture"), which
+is treated specially during the direct calculation and when viewing the
+material.
+Based on the BSDF data, the coefficient of specular transmission is
+determined and used for modifying unscattered shadow and view rays.
+.DS
+mod aBSDF id
+5+ BSDFfile ux uy uz funcfile transform
+0
+0|3|6|9
+     rfdif gfdif bfdif
+     rbdif gbdif bbdif
+     rtdif gtdif btdif
+.DE
+.LP
+If a material has no specular transmitted component, it is much better
+to use the BSDF type with a zero thickness than to use aBSDF.
+.LP
 .UL Antimatter
 .PP
 Antimatter is a material that can "subtract" volumes from other volumes.
@@ -1569,6 +1595,18 @@ the Ecole Polytechnique Federale de Lausanne (EPFL Uni
 in Lausanne, Switzerland.
 .NH 1
 References
+.LP
+Wang, Taoning, Gregory Ward, Eleanor Lee,
+``Efficient modeling of optically-complex, non-coplanar
+exterior shading: Validation of matrix algebraic methods,''
+.I "Energy & Buildings",
+vol. 174, pp. 464-83, Sept. 2018.
+.LP
+Lee, Eleanor S., David Geisler-Moroder, Gregory Ward,
+``Modeling the direct sun component in buildings using matrix
+algebraic approaches: Methods and validation,''
+.I Solar Energy,
+vol. 160, 15 January 2018, pp 380-395.
 .LP
 Ward, G., M. Kurt & N. Bonneel,
 ``Reducing Anisotropic BSDF Measurement to Common Practice,''