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PointingModelOffsets » History » Version 12

Lucas Beaufore, 07/12/2013 12:53 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 effect of the corrections are arguably more visible on a 3D plot. The following show the tweak values and exposure ID values (essentially time, in order to better show the exposure groups)
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versus the offsets.
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Blue = Original offsets
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Green = Original offsets + (.0176 * trim)
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Red = Original offsets - (.0176 * trim)
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Declination offsets vs trim_dy (vs expid):
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|!{width:100%}dec_all_corrections_back.png! | !{width:100%}dec_all_corrections_side.png! | 
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RA offsets vs trim_dx (vs expid):
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|!{width:70%}ra_all_corrections_side.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 (green) makes each set of four data points taken in the same position much more horizontal, removing correlation with trim values.
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Subtracting the correction makes each set of four data point correlate much more strongly 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. Each set of graphs
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has the correction applied in both directions.
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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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Correction added and correction subtracted, respectively
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|!{width:100%}dec_corrected_teldec_ha.png! |!{width:100%}dec_neg_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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Correction added and correction subtracted, respectively
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|!{width:100%}ra_corrected_teldec_ha.png! |!{width:100%}ra_neg_corrected_teldec_ha.png! |
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P3. Interesting observations
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By adding the correction, the range of offsets decreases, and the correlation of the offsets with trim values is mostly removed. However, the offsets are on average FARTHER from 0
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By subtracting the correction, the range of offsets increases, and the correlation of the offsets with trim values is mostly remvoed. However, the offsets are on average CLOSER to 0.