--- ray/doc/man/man1/rtpict.1	2019/07/23 18:17:54	1.3
+++ ray/doc/man/man1/rtpict.1	2020/05/06 14:23:18	1.6
@@ -1,4 +1,4 @@
-.\" RCSid "$Id: rtpict.1,v 1.3 2019/07/23 18:17:54 greg Exp $"
+.\" RCSid "$Id: rtpict.1,v 1.6 2020/05/06 14:23:18 greg Exp $"
 .TH RTPICT 1 3/19/2018 RADIANCE
 .SH NAME
 rtpict - generate a RADIANCE picture or layerd image using rtrace
@@ -62,12 +62,12 @@ in the specified directory:
 .sp
 .nf
 v	radiance.hdr
-r	mirrored.hdr
-x	unmirrored.hdr
-l	effective.dpt
-L	firstsurface.dpt
-R	mirrored.dpt
-X	unmirrored.dpt
+r	r_refl.hdr
+x	r_unrefl.hdr
+l	d_effective.dpt
+L	d_firstsurf.dpt
+R	d_refl.dpt
+X	d_unrefl.dpt
 n	perturbed.nrm
 N	unperturbed.nrm
 s	surface.idx
@@ -84,7 +84,8 @@ converted to a 16-bit representation by
 .I rcode_depth(1),
 and the
 .I \-d
-option should be used to assign the reference (median) depth and units.
+option should be used to assign the reference (median) depth and world
+units, which applies to the overall scene.
 Surface normals (from the 'n' and 'N' types) will be converted
 to a 32-bit representation by
 .I rcode_normal(1).
@@ -108,6 +109,25 @@ rtpict -n 4 -vf mypers.vf -ab 1 -af scene.amb scene.oc
 To render radiance, first surface distance, and normals in a layered image:
 .IP "" .2i
 rtpict -n 8 -vf fish.vf @render.opt -ovLn fisholay scene.oct
+.SH NOTES
+Users should seriously consider using
+.I rpiece(1)
+when irradiance caching is employed with a shared ambient file.
+If
+.I rtpict
+is used in multiprocessing mode with a shared irradiance cache,
+it is trying to compute almost
+the same part of the same scanline in different processes, which
+results in many redundant calculations.
+The
+.I rpiece
+program avoids this by working on separate tiles in each
+process, with less overlap in the indirect irradiance calculation.
+Either program will benefit from an "overture" run of a
+single-process rpict to create the ambient file using a low-resolution
+rendering that is discarded, but this will not completely solve the
+problem for
+.I rtpict.
 .SH AUTHOR
 Greg Ward
 .SH "SEE ALSO"