Author: DM WG

Date last changed: 2018-11-16

Date accepted:

This erratum is to correct an error reported at the IVOA interop in Victoria, BC: May 2018

cite:

*The formula in Section 4.5.1.4 (pg 30: Region.Polygon) states"The summation is over determinants of matrices formed by the position vectors xi of successive vertices; xn+1 = x1. In spherical space (left-handed coordinates) the area is:*

A = - SUM[ α(i) ] – (n-2) *pi

A = (RA,DEC)[0] = (90, 0)

*B = (RA,DEC)[1] = (0, 0)C = (RA,DEC)[2] = (0, 90)*

The three angles of the polygon are all 90 deg, or pi/2 rad by construction. A in the above case is: -3 * pi/2 –pi = -5/2 pi

The correct formula is:

A =

- 4.5.1.4 page 30

A = + SUM[ α(i) ] – (n-2) *pi

Software using the wrong formula must be updated

- We need to confirm that the example has considered the 'left-handed' vs 'right-handed' qualifiers from the text.

Topic revision: r3 - 2018-12-19 - LaurentMichel

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