| | 3 | === Circularization === |
| | 4 | |
| | 5 | When ppStack generates a target PSF, it does so by taking the envelope of a "circularized" realization of the input PSFs. This appears to work fine for PSFs that are already circular, but for highly elliptical PSFs, this breaks down for unknown reasons. As an example, the following figure shows the PSF grid for input 14 for a certain SAS stack. The target grid shown in the middle is dominated by the large size of input 14. However, disabling circularization creates the field shown in the right panel. The circularized form seems much larger than expected from this elongated PSF. Looking at the profiles along the major and minor axis and comparing this to the circularized form shows that there is an error somewhere in this calculation. |
| | 6 | |
| | 7 | [[Image(circular_example.jpg)]] |
| | 8 | |
| | 9 | [[Image(circularized.png)]] |
| | 10 | |
| | 11 | The effect of this circularization error is that the input PSF cuts work on a PSF radial profile corresponding to the elliptical form. This produces a FWHM on the order of 4. This is below the threshold, and is therefore accepted. However, upon circularization, the FWHM balloons to ~11, resulting in a target PSF of ~11. This likely explains some of the unexpected jumps in target FWHM from a "well behaved" set of inputs. |
