MPO Canopus - FITS/SBIG Header Editor
The main purpose behind the header editor is to allow correcting the date and/or time
of an image due to computer problems or to modify some of the "comment" fields,
such as instrumentation, the position of image center, and so on. Some fields cannot be
edited, even though they are displayed. Mostly these are values that, if modified, would
render the image unreadable, e.g. the number of pixels per row or column. These are shown
as dark gray fields.
The editor also allows adding additional standard keywords and associated values.
It cannot be emphasized enough that using the header editor requires great
care. If used incorrectly, an image can be rendered unreadable. It is a very
good idea to backup any images that you intend to edit, just in case something does not go
as planned.
Forced Formatting vs. Free Form Data Entry
Some header editors allow you to enter data with little or no validation. This can
cause a number of problems when trying to read the image header after it is modified. On
the other hand, forcing the format of many of the data fields can lead to problems when
the original data was not stored in that format.
For example, the MPO editor assumes the OBJCTRA field has a format of HH:MM:SS.sss. If
another program stored the data with fewer characters than in that "picture
mask", then the data doesn’t look quite right when displayed in the editing
field. In such a case and you do not need to modify the OBJCTRA field, then do not edit
the original data. It will be saved "as-is". However, if you do need to modify
the data, you must enter a value that exactly fills the expected data mask.
In addition to forcing the format of data entry, the editor also forces the data type
for a given keyword. To help avoid the proliferation of non-standard keywords, only a
limited number of keywords are allowed and no user-defined keywords can be added to a
header. These restrictions are in place to help avoid making your images unreadable. The
Canopus documentation contains a list of the accepted keywords and its allowed data
format. |
