Trouble-shooting

This section contains a few hints and tips which may be useful when unexpected behaviour is encountered while using POLPACK:

``POLPLOT cannot align the vector map with a previously displayed image''

- If you use the CURSA application XCATVIEW to create a catalogue, you should ensure that textual information is stored with the output catalogue. This is done by selecting the appropriate option when you use the Save command in the File menu. The textual information stored with a POLPACK catalogue contains the information describing how to align the vectors with other co-ordinate systems, and so failure to copy this information will mean that the output catalogue cannot be aligned with other images.

``Command not found''

- Have you started up POLPACK as described here?

``POLIMP will not accept my IRAF/FITS/etc. data files''

- Have you started up the CONVERT package has described here?

``Rendezvous file has disappeared!''

- If this message appears while using POLKA, you may have run out of disk space in your ADAM directory. Your ADAM directory is used to store files related to the operation of the ADAM parameter and message systems, and is usually a sub-directory named adam within your home directory. It may be changed to a new directory by assigning an alternative directory path to the environment variable ADAM_USER.

``POLKA cannot create any intermediate files''

- This may be due to lack of disk space. Intermediate files created by POLKA are stored in a sub-directory within the directory given by environment variable HDS_SCRATCH. Your current directory is used if HDS_SCRATCH is not defined. Check to see if the disk containing the appropriate directory is nearly full, or if your quote has been exceeded. If so, you can specify a different directory by setting HDS_SCRATCH to hold the required directory path. For instance,

% setenv HDS_SCRATCH /scratch5a/dsb/temp

would cause POLKA to put its intermediate files in /scratch5a/dsb/temp.

``POLKA seems to run very slowly''

- This can happen if the directory in which POLKA stores intermediate files is attached to a remote computer. Try changing the directory to one on your local disk by setting the HDS_SCRATCH environment variable before running POLKA.

``No browser appears when I try to use hypertext help in POLKA''

- The scheme used to activate the hypertext browser may not work for all combinations of browsers and operating systems. You may be able to get round this by specifying a different browser using the HTX_BROWSER environment variable. For instance, some revisions of netscape V4 fail to appear using POLKA under Digital UNIX V4. If you have a copy of netscape V3 you could use it instead by setting HTX_BROWSER to its path:

% setenv HTX_BROWSER /usr/local/bin/netscape.v3

replacing the example path with the correct path for your machine.

``POLKA always uses a private colour map''

- POLKA requires its own private colour table if there are other colour-greedy applications running when POLKA tries to create the image display area. The netscape hypertext browser is a common example. Shutting down such applications before running POLKA should get round the problem.

Note, if the parameter STARTHELP has a true value when running POLKA, then a hypertext browser will be created automatically before the image display area is created. If this causes a private colour map to be used, then you could disable the automatic creation of the hypertext browser by setting STARTHELP to a false value when running POLKA:

% polka starthelp=no

This need only be done once. Subsequent invocations of POLKA will use the same value for STARTHELP until a new value is specified on the command line. If necessary, you can still access the hypertext help using the Help menu button at the top right corner of the POLKA interface.

``The catalogue produced by POLVEC has lots of zero polarized intensity values in it''

- POLVEC can apply a correction to to the values of percentage polarization and polarized intensity to remove statistical bias introduced by the squaring and adding of the Stokes parameters $Q$ and $U$ (see POLVEC parameter DEBIAS). This can result in corrected percentage polarization values which are identically equal to zero if the original percentage polarizations are small and the corresponding variances are large. These zero percentage polarization values then result in zero polarized intensity values. Note, the $Q$ and $U$ values are not corrected in any way, since they already give unbiased estimates of the required quantities.