An IRAF package is available to help you take a quick look at your
INGRID data while you are observing at the telescope. Note that it is not
intended to provide fully reduced data ready for analysis.
When you take an exposure with INGRID the array is reset and
out. This is called the pre-read image, and is stored in extention 1 of
(rxxxxxx.fit). After the exposure time has passed the array is read
again. This is called the post-read image and is stored to the
extention 2 of file
(rxxxxxx.fit). It is the difference of these two images that is of
interest to the observer. The ingrid_ql
package provides a quick
way to access this information.
Using the INGRID quick look package
To use the INGRID quick look package from the WHT control room:
- Log onto the WHT data reduction
machine as whtguest
(with the password provided by your support astronomer).
- Open a display tool, such as ds9,
to display the data (eg. type ds9&).
- Start an IRAF session by opening an xgterm, changing to
the home directory and typing cl (or ncl). The prompt will change to cl>.
- Type: cl> ingrid_ql. The prompt will change
- Type: in>help usage, to get information
about the use of the package.
- Type: in>help to get a list of the available
- Type: in>help <task_name> to
get more information on using each particular task.
Some of the most frequently used tasks are:
| combine dithered images
|display frame (post-pre)
| find focus from focusrun images
| combine images
| find readout noise from two
| calculate and store post-pre
| list dark exposure times needed
|calculate image statistics
|subtract two images
You can also download the INGRID quick look package and install it
for your personal use:
- Download ingrid_ql-06092001.tar.gz. This gzip-ed tar file contains the IRAF quick look scripts for INGRID.
You can check the latest CHANGES to the package. IR UltraDAS is now used for INGRID. You need to
update INGRID_QL to work on data taken after 4 September 2001.
- To install follow the installation instructions in the file
While observing, the most useful tasks will probably be (i) to display
a single image and (ii) to quickly re-construct an image from a number
of images taken in a dither pattern.
Once you have taken an
exposure you will probably want to view it. This can be done with the idispframe
task. For example:
in>idisp r123456 1
will display exposure number 123456 in frame 1 of your display
You can then use imexamine to analyse this image. All
parameters for display are also available for idispframe. Additionally
if you want to subtract a sky frame from the image, before it is
displayed, you can use the parameters subsky and sky.
in>idisp r123456 1 subsky+ sky=sky_h
would subtract the image "sky_h" from "r123456" and display the
resulting image. A quick
and dirty way to subtract a sky image is to use an exposure from a
different field as the sky image, for example:
in>idisp r123456 1 subsky+ sky=r123455
This task can be used to combine a set of dithered images.
Changing the match parameter will select one of three methods
for computing the offsets between the images:
- match="wcs" This is the most automatic way. The wcs
coordinates, generated from the
telescope pointing information, is used to calculate the offsets
- match="pick1" This method is semi-automatic. The first
image is displayed and you have to pick a star with the 'm' key that
visible on every following image. The task calculates where the
star should be on each image (from the telescope pointing information)
then uses imcentroid to get the exact offset.
- match="manual" This method is completely manual. Every
image is displayed and you have to pick the same star on every image.
positions of the stars are then refined using imcentroid and used for
calculating the image offsets.
Eg. To reassemble a 5 point dither using the "pick1" method, and
store the result in a file named "comb", use:
As usual, you can also use lists to specify the input files. The
following example would combine all files listed (one file per line) in
the file allfiles, using the telescope pointing
information, and put the
output into a file named allcomb:
in>idedither @allfiles allcomb match="wcs"