https://pfspipe.ipmu.jp/jira This file is an XML representation of an issue en-us 8.3.4 803005 13-09-2019 https://pfspipe.ipmu.jp/jira/browse/PIPE2D-547 DRP 2-D Pipeline <p>Investigate the problem of negative values reported by <a href="https://pfspipe.ipmu.jp/jira/secure/ViewProfile.jspa?name=price" class="user-hover" rel="price">price</a> in pfspipe.ipmu.jp/jira/browse/<a href="https://pfspipe.ipmu.jp/jira/browse/PIPE2D-333" title="Construct a 1D LSF from a 2D PSF" class="issue-link" data-issue-key="PIPE2D-333"><del>PIPE2D-333</del></a>. </p> PIPE2D-547

Investigate and solve the problem of negative values in LSF

Task Major Done Done ncaplar ncaplar Fri, 10 Apr 2020 13:51:37 +0000 Mon, 4 Jan 2021 20:23:15 +0000 Tue, 14 Apr 2020 14:28:02 +0000 0 2 <p>This is my priority for the week starting April 12</p> <p>I have evaluated what LSF would I expect at the position that <a href="https://pfspipe.ipmu.jp/jira/secure/ViewProfile.jspa?name=price" class="user-hover" rel="price">price</a> mentioned (fiber=339, wavelength=800nm, i.e., at x=1765 and y=2021). I get the result shown in the Figures (LSF_Neven_fiber339_wavelength_800.png and LSF_Neven_fiber339_wavelength_800_in_2d.png). I see no negative values in either 1d or 2d. </p> <p>The way forward:</p> <p>1. I will investigate if I ever see any negative values on my own computer.<br/> 2. If I never see any negative values, I have to investigate further from where did these negative values appear. </p> <p>I never see any negative values in any of my PSFs and LSFs at 1600 spots across the detector. I am concluding, based on this, that the negative values are happening ``somewhere'' downstream. I am investigating. </p> <p>Paul correctly pointed out that I was investigating the different input data (I was using Sep12, and the default input data was Sep11). With this input set, I did find some positions that have negative values for their predictions.</p> <p>Basically what happens is: </p> <p>1. the algorithm selects two points on the same side (e.g., both below the wanted point or above the wanted point)</p> <p>2. the algorithm does linear interpolation, and if these two inputs are nearby and the wanted point is far away, a small gradient can produce large enough difference that the predicted value drops below 0.</p> <p>This is illustrated in Figure ``Interpolation_effect.png''.</p> <p>The effect is more likely to happen in the areas of sparse data, as input data points are far away (Shown in ``where_the_data_is.png''). This is why we get negative values in the center where there are few input PSF spots.</p> <p>The problem will go away with a denser sampling of input points, as part of <a href="https://pfspipe.ipmu.jp/jira/browse/PIPE2D-521" title="Create global PSF solutions for the July 2019, using 2020 improvments" class="issue-link" data-issue-key="PIPE2D-521"><del>PIPE2D-521</del></a>, but the creation of that datasets is probably at least a week away.</p> <p>This was discussed on the technical telecon on Apr 13/Apr 14. The conclusions:</p> <p>In the short term:</p> <ol> <li>Finish <a href="https://pfspipe.ipmu.jp/jira/browse/PIPE2D-521" title="Create global PSF solutions for the July 2019, using 2020 improvments" class="issue-link" data-issue-key="PIPE2D-521"><del>PIPE2D-521</del></a></li> <li> Modify the Interpolation algorithm that is always positive definite</li> </ol> <p>In the longer term:</p> <p>     1. Improve the interpolation algorithm, and see how to get best results</p> <p>I'm not at all surprised that interpolation leads to negative values, it was certainly the explanation that came to mind. I assume that most are very close to zero.</p> <p>This problem should go away once we interpolate the pupil illumination/Zernikes</p> <p>I have added Figure ``Interpolation_effect_with_April1520_version.png'' showing that at the same location that we had negative values in the previous version, LSF is well behaved using the newest version of the spots. I still have to investigate if this is the case across the full detector plane.</p> Relates PIPE2D-347 PIPE2D-333 Development Rank 0|02qps0:39 Reviewers hassan Sprint 2DDRP-2021 A Story Points 4.0