From: Marc Mendez (mmendez++at++silicon-worlds.fr)
Date: 02/01/2002 04:15:22
Hi Performers,
I m really in a bad situation here and need a pfExpert in matrixes.
Here is my problem.
I try to visualize an object around the Earth. To compute its position, I ve got
three data : radius, latitude, longitude.
For the moment it looks easy.
But that object originally has a coordinate system that is R0 (X0, Y0, Z0).
Once in space, its coordinate system is Rs (Xs, Ys, Zs).
The constraints for its positionning are :
- put it at the right place (that is OK),
- set its nominal attitude (ie orientation) :
Zs must be colinear to the position vector (that means -Zs should point
the center of the Earth) AND,
-Ys (minus Ys) must be colinear to the speed vector (which means that the
object shouldn t turn around its Zs axis when flying).
I used that to put that thing pfCorrectly :
input : position_vector, speed_vector, radius, latitude, longitude.
translation_matris.makeTrans(0, 0, radius);
z_attitude_matrix.makeVecRotVec(Zs, position_vector);
y_attitude_matrix.makeVecRotVec(-Ys, speed_vector);
total_matrix = translation_matrix * y_attitude_matrix * z_attitude_matrix;
But every time I cross the Equator, I got a 180° rotation around the Zs axis
(which means that the y_attitude_matrix is incorrect, the z_attitude_matrix has
been checked alone and doesn t derive).
Any idea, suggestion, source code (8))))) ???
Lot of pfThanks in advance,
Marc.
-- Marc Mendez Silicon Worlds SA12, rue de Chatillon 75014 Paris Tel : +33 (01) 53 90 11 13 Fax : +33 (01) 53 90 11 12
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