Matrice

Identity Matrix

Each call to transformation functions are cummulative. Each time those functions are called, the appropriate matrix is constructed and multipled by the current modelview matrix. The new matrix then becomes the current modelview matrix, which is then multiplied by the next transformation, and so on.

In order to reset the coordinate system back to the center of origin of the eye coordinate system -- we load the modelview matrix wit hteh identity matrix. Identity matrix specifies that no transformation is to occur -- all cooridnates we specify when drawing are eye coordinates.

Loading the identity matrix means that no transformations are performed on the vertices. This is how you do it:

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

First line specifies that the current operating matrix is the modelview matrix. After the current operating matrix is sent, it remains active until you change it. Second line loads the current matrix (modelview matrix in this case) with the identity matrix.