View source for Model Space and Camera Space

Objects are defined in a Cartesian coordinate system, i.e. as xyz
coordinates for each atom (or surface point or corner or...). This
coordinate system is model space. To make objects visible, PyMOL
places a "camera" such that it sees most of the molecule. The picture
that is shown on the screen is the image that is taken by the
camera. Initially, after loading an object, the camera is placed such
that it looks on the object parallel to the z axis. x and y axes are
horizontal respectively vertical. In the beginning, the axes
correspond to the physical directions of the screen: x and y are
horizontal /vertical, z is perpendicular to the screen.  To change the
view, normally the camera is moved: view of all the objects is changed
simultaneously, the objects are not moved relative to each
other. After changing the view, x, y and z axes don't correspond to
the directions of the screen anymore.

turn, move, center, zoom, orient and mouse action in viewing mode move the
camera in object space.

For easy description of object movement relative to the camera, an
additional coordinate system is defined: Camera space. The camera is
situated in the origin of camera space, x and y are horizontal
respectively vertical and z is the viewing direction. Camera space
always corresponds to the directions of the screen.

The relation of camera space and model space is described in the view matrix. (See
get_view). 

Changing the coordinates in model space is only necessary when objects shall
be moved relative to each other or when the transformed coordinates
are to be written into a file. 

Model space coordinates can be changed with the commands rotate and
translate, transform_selection or with the mouse in editing mode.



== Space and File saving ==

When  model coordinates are saved (e.g. as a pdb file), PyMOL uses
model space coordinates. In contrast, when an image is saved as povray
or vrml, camera space coordinates are used. When image files in model
space coordinates are needed, first choose colors and representations
as needed, then align camera space to model space:

<source lang="python">
set_view (\
     1,    0,    0,\
     0,    1,    0,\
     0,    0,    1,\
     0,    0,    0,\
     0,    0,    0,\
     0,    300,  1 )
</source>

After setting the view, the molecule will probably be out of sight but
anyway it will be saved to the file. This can be used e.g. to receive
a list of surface points in model space.


----

== See Also ==

[[turn]], [[move]], [[center]], [[zoom]], [[orient]], [[rotate]], [[translate]], [[Transform_selection]], [[Get_View]]

[[Category:Advanced Issues|Camera Space/Model Space]]
[[Category:Concepts|Camera Space/Model Space]]