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QC
PLOTS |
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CURRENT |
HISTORY |
X0
and Y0 |
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translational matrix
coefficients |
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rotational matrix
coefficients |
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image quality |
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ellipticity |
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QC1
database (advanced users): browse
| plot |
Click on CURRENT
to see the current trending (Health Check).
Click on HISTORY
to see the historical evolution of the trending. |
The Mask to CCD Transformation Matrix translates mask
coordinates into CCD pixels. It is determined with special MOS masks having
pinholes on a regular grid. Measurements using these mask are typically
executed once a day for health check purposes. Since August 2010, these frames are also used to check the VIMOS focus.
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Example MOS pinhole mask image |
top
Mask
to CCD transformation parameters |
The transformation matrix has the following form:
X = a_xx * x + a_xy * y + x_0
Y = a_yx * x + a_yy * y + y_0
with (x,y) being mask coordinates in mm and (X,Y) CCD
coordinates in pixels. X direction is along the slit orientation, y direction
is perpendicular to the slits (i.e. in dispersion direction).
The matrix coefficients a_xx, etc. and the zeropoints
x_0 and y_0 are determined from the pinhole image for each quadrant. The
diagonal coefficients a_xx and a_yy give the scale factor between mask
and CCD (around 8.4 pixels/mm). The coefficients a_xy and a_yx give the
rotation and are nearly zero.
QC1 parameters
parameter |
QC1 database: table, name
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procedure |
x_0 |
vimos_mask2ccd, x0 |
x0 coefficient of mask to CCD transformation |
y_0 |
vimos_mask2ccd, y0 |
y0 coefficient of mask to CCD transformation |
a_xx |
vimos_mask2ccd, xx |
xx coefficient of mask to CCD transformation |
a_xy |
vimos_mask2ccd, xy |
xy coefficient of mask to CCD transformation |
a_yy |
vimos_mask2ccd, yy |
yy coefficient of mask to CCD transformation |
a_yx |
vimos_mask2ccd, yx |
yx coefficient of mask to CCD transformation |
From the pinhole images, also QC parameters for checking the focus are calculated. These are image quality (as FWHM in pixels of the major axis fo the pinhole ellipses), ellipticity, and orientation (of the pinhole ellipses). Each quadrant is divided into 3x3 sub cells (squares). All parameters and their standard deviations are calculated in each cell and globally per quadrant.
QC1 parameters
parameter |
QC1 database: table, name |
procedure |
pinhole_count |
vimos_mask2ccd, pinhole_count |
total number of identified pinholes per quadrant |
image_quality_mean |
vimos_mask2ccd, image_quality_mean |
averaged image quality per quadrant |
image_quality_rms |
vimos_mask2ccd, image_quality_rms |
standard deviation of image quality per quadrant |
ellipticity_mean |
vimos_mask2ccd, ellipticity_mean |
averaged ellipticity per quadrant |
ellipticity_rms |
vimos_mask2ccd, ellipticity_rms |
standard deviation of image quality per quadrant |
orientation_mean |
vimos_mask2ccd, orientation_mean |
averaged orientation of pinhole ellipses per quadrant |
orientation_rms |
vimos_mask2ccd, orientation_rms |
standard deviation of orientation per quadrant |
iq_mean_cell[1-9] |
vimos_mask2ccd, iq_mean_cell[1-9] |
averaged image quality in each cell (per quadrant) |
iq_rms_cell[1-9] |
vimos_mask2ccd, iq_rms_cell[1-9] |
standard deviation of image quality in each cell |
ellip_mean_cell[1-9] |
vimos_mask2ccd, ellip_mean_cell[1-9] |
averaged ellipticity in each cell |
ellip_rms_cell[1-9] |
vimos_mask2ccd, ellip_rms_cell[1-9] |
standard deviation of ellipticity in each cell |
orient_mean_cell[1-9] |
vimos_mask2ccd, orient_mean_cell[1-9] |
averaged orientation in each cell |
orient_rms_cell[1-9] |
vimos_mask2ccd, orient_rms_cell[1-9] |
standard deviation of orientation in each cell |
History
date |
event |
2011-05 |
tilt between focal plane and detector plane fixed, image quality and ellipticity improved; there is, however, a dependency between ellipticity and temperature |
2011-08-27 |
Q3 out of focus, fixed 2011-09-06 |
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