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PointingModelOffsets » History » Version 18

Lucas Beaufore, 07/12/2013 01:51 PM

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h1. Pointing Model Offsets
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In order to study the effects the pointing model may have on the offsets, new offsets were calculated with possible corrections from the effects of the hexapod trim values.
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The following histograms show the distribution of the offsets before trim corrections, and with a trim correction of both addition and subtraction.
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RA offset with: No correction, addition of a scaled (.0176 arcsec/micron) trim_dy value, subtraction of the scaled trim_dy value
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|!{width:100%}dec_standard.png! |!{width:100%}dec_corrected_y.png! | |!{width:100%}dec_corrected_minus_y.png! |
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Dec offset with: No correction, addition of a scaled (.0176 arcsec/micron) trim_dx value, subtraction of the scaled trim_dx value
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|!{width:100%}ra_standard.png! |!{width:100%}ra_corrected_x.png! | |!{width:100%}ra_corrected_minus_x.png! |
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The following plots show how adding the trim correction removes the correlation between trim values and the correspoding offsets. The 
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colors correspond to exposure IDs, approximately time, to help distinguish between exposure sets.
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RA offset corrected with trim_dx value:
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No correction, correction added
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|!{width:100%}color_ra_trim_dx.png! |!{width:100%}color_ra_trim_corrected_trim_dx.png! |
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Declination offset corrected with trim_dy value:
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No correction, correction added
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|!{width:100%}color_dec_trim_dy.png! |!{width:100%}color_dec_trim_corrected_trim_dy.png! |
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By applying trim corrections, the offsets should no longer include the part of the offset due to hexapod corrections.
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As can be seen, adding the correction makes each set of four data points taken in the same position much more horizontal, removing correlation with trim values.
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After applying the correction, the offsets can then be reexamined for correlations with the telescopes position. The plots below illustrate the relations. 
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The following two plots show the Declination offsets plotted against the declination of the telescope. The color scale shows the HA of the telescope.
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No correction, correction added
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|!{width:100%}dec_teldec_ha.png! |!{width:100%}dec_corrected_teldec_ha.png! |
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The following two plots show the RA offsets plotted against the declination of the telescope. The color scale shows the HA of the telescope.
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No correction, correction added
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|!{width:100%}ra_teldec_ha.png! |!{width:100%}ra_corrected_teldec_ha.png! |