--- ray/src/util/glarendx.c	1991/05/02 14:00:58	1.9
+++ ray/src/util/glarendx.c	1992/11/19 09:59:08	2.3
@@ -127,8 +127,8 @@ char	*s;
 
 	if (print_header)		/* copy to output */
 		fputs(s, stdout);
-	if (!strncmp(s, VIEWSTR, VIEWSTRL))
-		sscanview(&midview, s+VIEWSTRL);
+	if (isview(s))
+		sscanview(&midview, s);
 	else if (isformat(s)) {
 		formatval(fmt, s);
 		wrongformat = strcmp(fmt, "ascii");
@@ -289,6 +289,8 @@ FVECT	sd, vd, vu;
 	d = DOT(sd,vu)/sqrt(1.0-d*d);
 	if (d >= 1.0)
 		tau = 0.0;
+	else if (d <= -1.0)
+		tau = 180.0;
 	else
 		tau = acos(d) * (180./PI);
 	return( exp( sigma*( (35.2 - tau*.31889 - 1.22*exp(-.22222*tau))*1e-3