This page (revision-27) was last changed on 26-Oct-2022 21:57 by Peter Young

This page was created on 07-Jun-2010 19:35 by PeterYoung

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26 07-Dec-2016 14:14 6 KB Peter Young to previous | to last
25 05-Apr-2011 18:14 6 KB PeterYoung to previous | to last
24 08-Jul-2010 15:42 6 KB PeterYoung to previous | to last
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EISmethods
EISmethods

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At line 32 changed one line
The heliocentric coordinates for the data are given by
The heliocentric coordinates for the center of a raster at a given wavelength, WVL, are obtained with:
At line 34 changed 2 lines
{{{IDL> xpos=data->getxpos()
IDL> ypos=data->getypos()}}}
{{{
IDL> xcen=data->getxcen(/raster)
IDL> ycen=data->getycen(wvl,/raster)
}}}
At line 37 changed one line
XPOS gives the X-coordinate for each slit position and YPOS gives the position for each pixel in the Y direction. The X-coordinate given includes the jitter (in X) that was recorded by the AOCS system as well as the telescope tracking, the pixel position (Y-coordinate) given does not, but is rather based on the ycen at exposure '0'. In case the latter is desired for exposure 'n' then the (ycen(n)-ycen(0)) should be added to ypos(n) (see below).
More details about EIS pointing information are given on the wiki page [Obtained pointing information from EIS data|EISPointing].
At line 39 removed one line
In addition, the coordinates of the reference point used in the data object are given by
At line 41 removed 15 lines
{{{IDL> xcen=data->getxcen()
IDL> ycen=data->getycen()}}}
These points are defined to be the home position of the fine mirror in X including telescope tracking and jitter, and the middle of the physical slit in Y including jitter. Note that this definition differs from that given in the FITS file header where XCEN and YCEN refer to the center of the raster (at the beginning of the observation). Thus, the center of the raster can be accessed by
{{{IDL> xcen=data->getinfo('XCEN')
IDL> ycen=data->getinfo('YCEN')}}}
or, perhaps more reliably (especially as concerns older data), by taking the average of the extreme values given by the xpos and ypos methods. As of early July 2010 a keyword, '/raster', has been added to the XCEN and YCEN methods. Setting this keyword gives the center of the raster at the time of the beginning of the raster (DATE_OBS), i.e. by calling
{{{IDL> xcen_raster=data->getxcen(/raster)
IDL> ycen_raster=data->getycen(/raster)}}}
Note that each of these method calls (except the last) returns an array of same size as the number of exposures. This is because the center of the raster moves with time due to spacecraft tracking and jitter.
This page (revision-27) was last changed on 26-Oct-2022 21:57 by Peter YoungTop