Coordinates spaces and detector geometry

This page is part of the ING document INS-DAS-29: Operations manual for UltraDAS..
This revision applies to the software in observing-system s9; it does not apply to system s8.

Complexity warning

To support all the various cameras and observing modes needed at ING, the system uses a very generalized system of coordinates to describe detector geometry.  The power of this system makes it complex to work with.

However, tools are on hand to make this easier. At this point, you should investigate the observing-system programme udas_geometry: that programme may tell you all you ever need to know about coordinates in UltraDAS.  Alternatively, see the pictorial examples below: these may explain sufficiently. If you really want to know the details, read on.

Tedious details

Three coordinate systems are important when observing UltraDAS: D-space is important to you as an observer because all readout windows are set using d-space coordinates. The relationship between d-space, r-space and i-space is important because it relates known cosmetic features of the detector to pixel positions in the output image.

For simple, single-output cameras, i-space, r-space and d-space are usually the same thing. In some cameras, i-space is different to r-space because the data are re-oriented before filing. In multi-output cameras, there are multiple r-spaces and things can get quite complex.

Areas of these coordinate spaces are often expressed in IRAF's image-section notation: [x1:x2,y1:y2]  means the sub-raster running from pixel  x1 to x2 inclusive, and from pixel y1to y2 inclusive.

These are points to bear in mind:

This is a precis. For full details, see the document  INS-DAS-19 coordinate systems for UltraDAS .

Graphic examples

The following pictures show how r-space, d-space and i-space are related for representative cameras.

In each picture, the light-sensitive areas are drawn in white and the bias regions, if any, in light grey. The legend on each section of the deetctor is in three parts:

  1. Output-channel number / chip name / amplifier name.
  2. Extent of the light-sensitve area, in d-space.
  3. Extent in d-space of the area read out, including bias regions.
The axes are those of d-space.

The pictures, incidentally, are the output of the udas_geometry programme, which is working directly from UltraDAS' configuration database.  That is, the pictures are exactly how the DAS thinks the detector works, and do not involve a manual transcription of the geometry.

Tektronix CCDs

Tektronix CCD



INT Wide-Field Camera