.. _background:

Background
==========
Page with general background information about tracking and alignment.

UVW Coordinates
---------------
The sensor-local coordinates are labeled UVW and are different from the
global XYZ coordinates by a translation and rotation. The rotations are
mostly small deviations from parallel or antiparallel.

Front
^^^^^
.. image:: _static/uvw-coord-front.png
   :width: 600
   :alt: Diagram Showing UVW Coordinates for Front of Detector

Back
^^^^
.. image:: _static/uvw-coord-back.png
   :width: 600
   :alt: Diagram Showing UVW Coordinates for Back of Detector

UChannel Ball and Pin Frames
----------------------------
The uchannel has two coordinate systems, called ball and pin frame, respectively. In the diagrams below, the front of the uchannel is on the right side, the back is on the left.

Top
^^^
.. image:: _static/uchannel_top.png
   :width: 600
   :alt: Diagram Showing Ball and Pin Frame Coordinate Systems for Top of UChannel, right=front, left=back

Bottom
^^^^^^
.. image:: _static/uchannel_bottom.png
   :width: 600
   :alt: Diagram Showing Ball and Pin Frame Coordinate Systems for Bottom of UChannel, right=front, left=back

Fixture Ball and Pin Frames
---------------------------
The fixture in which the sensors are measured also has two coordinate systems. The fixture pin frame is the same as the uchannel pin frame. The ball frames are different and share names because in both cases small metal balls are used to define the system.

.. image:: _static/fixture.png
   :width: 600
   :alt: Diagram Showing Ball and Pin Frame Coordinate Systems for Fixture