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From: yuan-liu@mails.tsinghua.edu.cn
Subject: From RAWX, RAWY to DETX, DETY
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Date: Mon, 24 May 2010 06:42:45 GMT
From: yuan-liu@mails.tsinghua.edu.cn
To: xmmhelp@sciops.esa.int
Cc: yuan-liu@mails.tsinghua.edu.cn
Subject: From RAWX, RAWY to DETX, DETY
Full_Name: Yuan Liu
Submission from: (NULL) (166.111.16.2)


In the document of task 'epevents', I found 
"epevents computes physical camera detector coordinates DETX, DETY (in the
CAMCOORD2 system) from raw detector coordinates RAWX, RAWY"

Would you please explain the method used to convert 'RAWX, RAWY' into 'DETX,
DETY' in detail, or point out some references? Thanks. 


Reply 1

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From: Pedro M. Rodriguez Pascual <xmmhelp@sciops.esa.int>
To: yuan-liu@mails.tsinghua.edu.cn
Subject: Re: From RAWX, RAWY to DETX, DETY (PR#43992)
Date: Mon May 24 09:30:52 2010
Dear Yuan Liu, 

The description of the XMM-Newton spatial coordinates systems can be found at

http://xmm2.esac.esa.int/external/xmm_sw_cal/calib/documentation/CALHB/node7.html

The parameters used for coordinates transformation within a given instrument are
stored in CCF files

EMOS1_LINCOORD_xxxx.CCF
EMOS2_LINCOORD_xxxx.CCF
EPN_LINCOORD_xxxx.CCF
RGS1_LINCOORD_xxxx.CCF
RGS2_LINCOORD_xxxx.CCF

The parameters needed for the transformation between instruments and Star
Tracker (i.e., celestial coordinates) are in 

XMM_BORESIGHT_xxxx.CCF

The SAS functions used in all spatial transformations in EPIC cameras are listed
in 

http://xmm2.esac.esa.int/external/xmm_sw_cal/calib/documentation/CALHB/node44.html

Sincerely,

Pedro



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From: "liuyuan" <comingliu@gmail.com>
To: "Pedro M. Rodriguez Pascual" <xmmhelp@sciops.esa.int>
Subject: Re: From RAWX, RAWY to DETX, DETY (PR#43992)
Date: Mon, 24 May 2010 22:20:05 +0800
Hi Pedro,

Thanks for your quick reply. I think I should make my question more specific.
I found the unit of DETX/Y (0.05 arcsec) is much smaller than the pixel size of
CCD (e.g. 4 arcsec for PN). So what is the rule used to allocate DETX/Ys of
events in the same pixel of CCD (i.e. with the same RAWX/Y)? Are they allocated
uniformly and randomly across the same pixel of CCD? If yes, what is the purpose
of this allocation? Thanks.

Best regards,
Yuan


----- Original Message ----- 
From: "Pedro M. Rodriguez Pascual" <xmmhelp@sciops.esa.int>
To: <yuan-liu@mails.tsinghua.edu.cn>
Sent: Monday, May 24, 2010 5:30 PM
Subject: Re: From RAWX, RAWY to DETX, DETY (PR#43992)


> 
> Dear Yuan Liu, 
> 
> The description of the XMM-Newton spatial coordinates systems can be found
at
> 
> http://xmm2.esac.esa.int/external/xmm_sw_cal/calib/documentation/CALHB/node7.html
> 
> The parameters used for coordinates transformation within a given
instrument are
> stored in CCF files
> 
> EMOS1_LINCOORD_xxxx.CCF
> EMOS2_LINCOORD_xxxx.CCF
> EPN_LINCOORD_xxxx.CCF
> RGS1_LINCOORD_xxxx.CCF
> RGS2_LINCOORD_xxxx.CCF
> 
> The parameters needed for the transformation between instruments and Star
> Tracker (i.e., celestial coordinates) are in 
> 
> XMM_BORESIGHT_xxxx.CCF
> 
> The SAS functions used in all spatial transformations in EPIC cameras are
listed
> in 
> 
> http://xmm2.esac.esa.int/external/xmm_sw_cal/calib/documentation/CALHB/node44.html
> 
> Sincerely,
> 
> Pedro
> 
> 
> 
> ================================================================================================
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> 
> The unauthorised disclosure, use, dissemination or copying (either in whole
or in part) of its content is prohibited.
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> If you received this message in error, please delete it from your system
and notify the sender.
> 
> E-mails can be altered and their integrity cannot be guaranteed.
> 
> ESA shall not be liable for any e-mail if modified.
> =================================================================================================
> 
>



Reply 2

Resend
From: Pedro M. Rodriguez Pascual <xmmhelp@sciops.esa.int>
To: comingliu@gmail.com
Subject: Re: From RAWX, RAWY to DETX, DETY (PR#43992)
Date: Mon May 24 14:35:40 2010
Hello,

The position of every single event is uniformly randomized at a sub-pixel scale
of 0.05arcsec; in the case of multiple (double, triple,...) events their
centroid is computed as a PI weighted sum over randomized sub-pixel coordinates
(to avoid aliasing effects). 

Finally, since the accuracy of the pointing attitude is better than pixel size,
as it is the pointing stability, the celestial location of a source can be
better determined after sub-pixel randomization.

Sincerely,

Pedro

> Hi Pedro,
> 
> Thanks for your quick reply. I think I should make my question more
specific.
> I found the unit of DETX/Y (0.05 arcsec) is much smaller than the pixel
size
of
> CCD (e.g. 4 arcsec for PN). So what is the rule used to allocate DETX/Ys
of
> events in the same pixel of CCD (i.e. with the same RAWX/Y)? Are they
allocated
> uniformly and randomly across the same pixel of CCD? If yes, what is the
purpose
> of this allocation? Thanks.
> 

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