I am a complete beginner in astronomy. While learning DS9, I came up with the following question.

Say I want to exclude a boxed region from an image FITS. The corresponding parameters according to Chandra is

  • Box = (xcenter,ycenter,width,height)
  • Box = (xcenter,ycenter,width,height,angle)

Although the name is self-explanatory yet I am confused about their respective units. What unit is used to label these parameters?


Usually pixel coordinates. What I would do is to let DS9 make a region file, as your documentation site says it supports them.

To do so:

  • Open file in ds9
  • From region->shape select the kind of region you want.
  • Click on edit->region
  • Draw the shapes you want (just click on the img)
  • Click region->save. In the coordinates box choose physical pixel coordinates.

Probably that should work... Good luck!


Several different units are possible. If you double click on the box a dialogue window will open where you can adjust the size/location. In the drop-down menus on the right hand site, you can choose which unit and coordinate system you want.

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