|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
[fitsbits] comment on SIP, optical distortion
080917 Dear Bill Pence and FITS community, reading about the proposed SIP conventions I would like to draw your attention to the most commonly seen, pure optical distortion (3rd order) term. This could be expressed with the SIP mechanism, however typically a single coefficient is applicable for many telescopes to control "distortion" (besides the knowledge of the "center" i.e. the location of the optical axis on the detector, which I see is already handled). Let D3 be the coefficient of (3rd order) optical distortion, and dx, dy the corrections to be applied to the x, y coordinates (e.g. in pixel unit), then dx = D3 * x * r**2 dy = D3 * y * r**2 with r**2 = x**2 + y**2 The SIP mechanism is more general but has the disadvantage that users (or people working on the calibrations of a detector) often try to solve for a full 3rd order polynomial, while the data might be better represented with just that single D parameter in order to keep the error propagation low. The D3 parameter is used since at least a century in the astrometric community, and having a FITS keywork mechanism for it as alternative option to the SIP for many applications would be good to have. Norbert ------------------------------------------------ Norbert Zacharias, Ph.D. Chief of Cataloging Division Astrometry Department US Naval Observatory voice: 202 762 1423 3450 Mass. Ave. NW fax: 202 762 1516 Washington, DC 20392 e-mail: ------------------------------------------------ |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
[fitsbits] Comments on image distortion conventions | Dick Shaw | FITS | 0 | September 18th 08 10:15 PM |
[fitsbits] Start of the 'INHERIT' Public Comment Period | Rob Seaman | FITS | 0 | April 6th 07 08:28 PM |
[fitsbits] Start of the 'INHERIT' Public Comment Period | Rob Seaman | FITS | 0 | April 6th 07 07:24 PM |
[fitsbits] Start of the 'INHERIT' Public Comment Period | Steve Allen | FITS | 0 | April 6th 07 06:27 PM |
[fitsbits] Comment Period on 2 FITS Proposals | William Pence | FITS | 0 | October 21st 04 09:56 PM |