headers: Tools for modifying image headers.

Introduction

There are several tasks in this package for examining and editing image headers---particularly GEIS format image headers. Type "help geis" for more information about the data structure for HST data. The `headers' package is implicitly loaded when ST4GEM is loaded. Placing these tasks in a separate package merely serves (in this case) to emphasize the logical relationship between them, and to make the package menu small and informative. A quick summary is given in Table 1 below, followed by a few highlights. Utilities for examining, editing, and reformatting images can be found in the `toolbox.imgtools' package.

              Table 1.  Image Header Utility Tasks
+--------------------------------------------------------------+
| Task        | Description                                    |
+--------------------------------------------------------------+
| hdiff       | Display differences between two headers        |
+--------------------------------------------------------------+

Header examination

There are three tasks for examining the image header contents. The `iminfo' task prints the values of some generally useful keywords that are found in most astronomical image headers, such as the image size, the integration time, the RA & Dec, UT and ST, etc. For HST data this task will print various, instrument-specific information, such as the filter(s)/grating(s) used, the instrument operating mode, etc. The two more general tasks are `hdiff', which prints the names and values of keywords that differ between pairs of images, and `hcheck' which will print the values of specified keywords based upon a user-specified condition. `hcheck' is quite general and is very useful for finding keyword values that are, e.g., out of range, or missing altogether.

Group format images

Users should be aware that modifications to GPB keywords must be performed explicitly on each group in multi-group GEIS files; the default is to operate on only the first image group. To learn the syntax for operating on individual image groups, type "help geis".

See also

toolbox.imgtools.

Type "help geis" for more information about GEIS format files.