--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/scripts/quaternion/qcoordinate_plot.m	Fri Dec 04 22:08:23 1998 +0000
@@ -0,0 +1,64 @@
+function qcoordinate_plot(qf,qb,qv)
+# function qcoordinate_plot(qf,qb,qv)
+# plot in the current figure a set of coordinate axes as viewed from 
+# the orientation specified by quaternion qv.  Inertial axes are
+# also plotted
+# qf: quaternion from reference (x,y,z) to inertial
+# qb: quaternion from reference to body 
+# qv: quaternion from reference to view angle 
+
+degrees = pi/180;
+d180 = 180*degrees;
+
+# construct coordinate transformation to view frame
+cm = qtransvmat(qv);
+p1 = [-1,-1,1]; p2 = [-1,-1,-1]; p3 = [1,-1,-1]; p4 = [ 1,-1, 1];
+p5 = [-1, 1,1]; p6 = [ 1, 1, 1]; p7 = [1, 1,-1]; p8 = [-1, 1,-1];
+# outline positive quadrant
+box1 = cm*[p4; p6; p5; p6; p7]';
+# outline rest of the box
+box2 =cm*[p7; p8; p5; p1; p4; p3; p7; p3; p2; p1; p2; p8]';
+
+# compute inertial to body rotation eigenaxis
+# qb = qbf*qf => qbf = qb/qf
+#
+# need to use inverse quaternion to rotate axes
+qbf = qinv(qmult(qb,qinv(qf)));
+
+[eaxv,th_eig] = quaternion(qbf);
+
+# draw 1/3 circle in x-y plane around a unit z axis
+th = (0:-12:-120)*degrees*sign(th_eig);    lth = length(th);
+cpts = [0 0 0.1*cos(th) ; 0 0 0.1*sin(th); 0 1 1*ones(1,lth)];
+
+# rotate the 1/3 circle around eigenaxis of inertial to body rotation
+# qez = qe/qz = rotation to get from z axis to eigenaxis.
+# This rotates the 1/3 circle from x-y plane to the plane normal to
+# eigenaxis
+qez = qmult(qbf,qinv(quaternion(0,0,1,0)));
+eig_xm = qtransvmat(qez);
+cpts = cm*eig_xm*cpts;
+
+# transform inertial and body quaternions to view coordinates (rotate
+# by azimuth, elevation)
+qfm = qtransvmat(qf);                 qbm = qtransvmat(qf);
+qf = qmult(qv,qf);                 qb = qmult(qv,qb);
+
+# get coordinate axes in inertial and reference frame
+jnk = qtransvmat(qf); ifv = jnk(:,1); jfv = jnk(:,2); kfv = jnk(:,3);
+jnk = qtransvmat(qb); ibv = jnk(:,1); jbv = jnk(:,2); kbv = jnk(:,3);
+
+gset size square
+axis([-2,2,-2,2]);
+[vv,theta] = quaternion(qb);
+xlabel(sprintf("rotate about eigenaxis %5.2f deg",th_eig/degrees));
+plot( [ibv(1),0],[ibv(3),0],"-@11;x (body);", ...
+	[0,jbv(1)],[0,jbv(3)],"-@21;y (body);", ...
+	[0,kbv(1)],[0,kbv(3)],"-@32;z (body);", ...
+	[ifv(1),0],[ifv(3),0],"-@13;x (inertial);", ...
+	[0,jfv(1)],[0,jfv(3)],"-@23;y (inertial);", ...
+	[0,kfv(1)],[0,kfv(3)],"-@34;z (inertial);", ...
+	cpts(1,:), cpts(3,:),".-6 ;eigenaxis;", ...
+	box2(1,:),box2(3,:),"-4;;", ...
+	box1(1,:),box1(3,:),"-5;;");
+endfunction