|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
[fitsbits] Start of the Public Comment Period on 2 Image DistortionConventions
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] Start of the Public Comment Period on 2 Image DistortionConventions | David W Hogg | FITS | 0 | September 30th 08 07:26 PM |
[fitsbits] Start of the Public Comment Period on 2 Image DistortionConventions | William Pence[_2_] | FITS | 0 | September 17th 08 09:21 PM |
[fitsbits] Start of the 'INHERIT' Public Comment Period | William Pence | FITS | 8 | April 8th 07 03:59 AM |
[fitsbits] Start of the 'INHERIT' Public Comment Period | Doug Tody | FITS | 0 | April 6th 07 11:59 PM |
[fitsbits] Start of "Tiled Image Compression" Public Comment Period | William Pence | FITS | 0 | November 15th 06 06:08 PM |