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MPO Canopus - FITS/SBIG Header Editor

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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.

 

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This page was last updated on 01/19/11 15:53 -0700.
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