<p><strong>Given the coordinates of an observation performed by XMM-Newton, is there a way to compute the coordinates of the limits of EPIC-PN's field of view?</strong></p>
<p>For instance, observation <code>0000110101</code> has coordinates <code>ra=64.897629 deg</code> (04h 19m 42.09s), <code>dec=56.022720 deg</code> (+55d 59' 58.0&quot;) and was made with an angle <code>pa_pnt=89.9568 deg</code> according to <a href="http://xmmssc.irap.omp.eu/Catalogue/4XMM-DR12/4xmmdr12_obslist.txt" rel="nofollow noreferrer">the observation list</a> used to compile the 4XMM-DR12 catalogue. When looking at the observation (see below), this point seems to be the middle of the field of view (FOV) of the overall observation, and ends up being a bit off the center of the PN FOV. I would like to compute the coordinates of the four corners.</p>
<p><a href="https://i.sstatic.net/V8sWo.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/V8sWo.png" alt="0000110101 PN image" /></a></p>
<p>Since the size of the FOV given by the spec of PN is 27.2 × 26.2 (<a href="https://www.aanda.org/articles/aa/abs/2001/01/aaxmm35/aaxmm35.html" rel="nofollow noreferrer">Table 1 of Strüder et al., 2001</a>, for the full frame mode) and the observation list gives an angle, I thought it would be easy but the offset bugs me off. I could not find any information about the consistency of the location of the observation center within PN's FOV in the XMM-Newton Users Handbook (see <a href="https://xmm-tools.cosmos.esa.int/external/xmm_user_support/documentation/uhb/epicmode.html" rel="nofollow noreferrer">here</a>, <a href="https://xmm-tools.cosmos.esa.int/external/xmm_user_support/documentation/uhb/pnchipgeom.html" rel="nofollow noreferrer">there</a> and <a href="https://xmm-tools.cosmos.esa.int/external/xmm_user_support/documentation/uhb/epic.html" rel="nofollow noreferrer">there</a>). Perhaps there is a tool in the SAS that can help, too. Or maybe these information are readily available in a PPS or ODF file associated to the observation.</p>

CC BY-SA 4.0
2023-06-14T16:47:54.323Z
Is there a World Coordinate System (WCS) in the FITS (?) image header ? If so, that would give a `CRPIX1/2` for the reference pixel and a `CRVAL1/2` for the coordinate values at the reference pixel. Along with the scale and skew which is also in the WCS and the number of pixels and gaps (looks to be multi-detector) that would let you work out where the corners are (Astropy has a [calc_footprint() method](https://docs.astropy.org/en/stable/api/astropy.wcs.WCS.html#astropy.wcs.WCS.calc_footprint) that can do this given the header)
astrosnapper
CC BY-SA 4.0
2023-06-15T03:39:16.163Z
What about the coordinates written on the edges of the image?
Pierre Paquette
CC BY-SA 4.0
2023-06-15T12:08:05.490Z
@PierrePaquette I would like to automate it. Manually annotate a large set of observations can become quite tiresome, and also error-prone.
Char siu
CC BY-SA 4.0
2023-06-15T12:09:16.223Z
@astrosnapper There is a WCS in the FITS header. Many thanks for pointing out the Astropy method, I'll try to get that working. It seems to be perfectly what I am looking for.
Char siu
<coordinate><xmm-newton>
Compute footprint of a region observed with EPIC-PN
Char siu
# Compute footprint of a region observed with EPIC-PN

(Asked by: username_0 on 2023-06-14)

**Given the coordinates of an observation performed by XMM-Newton, is there a way to compute the coordinates of the limits of EPIC-PN's field of view?**

For instance, observation `0000110101` has coordinates `ra=64.897629 deg` (04h 19m 42.09s), `dec=56.022720 deg` (+55d 59' 58.0") and was made with an angle `pa_pnt=89.9568 deg` according to [the observation list](http://xmmssc.irap.omp.eu/Catalogue/4XMM-DR12/4xmmdr12_obslist.txt) used to compile the 4XMM-DR12 catalogue. When looking at the observation (see below), this point seems to be the middle of the field of view (FOV) of the overall observation, and ends up being a bit off the center of the PN FOV. I would like to compute the coordinates of the four corners.

[![0000110101 PN image](https://i.sstatic.net/V8sWo.png)](https://i.sstatic.net/V8sWo.png)

Since the size of the FOV given by the spec of PN is 27.2 × 26.2 ([Table 1 of Strüder et al., 2001](https://www.aanda.org/articles/aa/abs/2001/01/aaxmm35/aaxmm35.html), for the full frame mode) and the observation list gives an angle, I thought it would be easy but the offset bugs me off. I could not find any information about the consistency of the location of the observation center within PN's FOV in the XMM-Newton Users Handbook (see [here](https://xmm-tools.cosmos.esa.int/external/xmm_user_support/documentation/uhb/epicmode.html), [there](https://xmm-tools.cosmos.esa.int/external/xmm_user_support/documentation/uhb/pnchipgeom.html) and [there](https://xmm-tools.cosmos.esa.int/external/xmm_user_support/documentation/uhb/epic.html)). Perhaps there is a tool in the SAS that can help, too. Or maybe these information are readily available in a PPS or ODF file associated to the observation.

**Tags:** coordinate, xmm-newton
> **Comments:**
> **username_1**: Is there a World Coordinate System (WCS) in the FITS (?) image header ? If so, that would give a `CRPIX1/2` for the reference pixel and a `CRVAL1/2` for the coordinate values at the reference pixel. Along with the scale and skew which is also in the WCS and the number of pixels and gaps (looks to be multi-detector) that would let you work out where the corners are (Astropy has a [calc_footprint() method](https://docs.astropy.org/en/stable/api/astropy.wcs.WCS.html#astropy.wcs.WCS.calc_footprint) that can do this given the header)  
> **username_2**: What about the coordinates written on the edges of the image?  
> **username_0**: @PierrePaquette I would like to automate it. Manually annotate a large set of observations can become quite tiresome, and also error-prone.  
> **username_0**: @astrosnapper There is a WCS in the FITS header. Many thanks for pointing out the Astropy method, I'll try to get that working. It seems to be perfectly what I am looking for.  

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## 0 answers

