RFC comments - SSIG: points of confusion

[mcdittmar]

From: https://wiki.ivoa.net/twiki/bin/view/IVOA/MeasRFC2

Points of confusion for me:

Section 2.1.1, "Pixelated Image Cube": I am not at all clear on what the term "pixel domain" means. In my mind, pixels are "image cells".
Section 2.1.1 and subsequently: What does it mean to be "dimensionally compatible"? Are Angstroms "dimensionally compatible" with Astronomical Units, for example, because they both measure length? Are percentages "dimensionally compatible" with everything, or nothing?

[mcdittmar]

Section 2.1.1, "Pixelated Image Cube": I am not at all clear on what the term "pixel domain" means. In my mind, pixels are "image cells".

Exactly. The pixel domain describes the image cells (which are outside of the Measurement scope, and handled by the Coordinates model). The image cell VALUE however, is within the Measurement scope.

Section 2.1.1 and subsequently: What does it mean to be "dimensionally compatible"? Are Angstroms "dimensionally compatible" with Astronomical Units, for example, because they both measure length? Are percentages "dimensionally compatible" with everything, or nothing?

Simply that a 1-dimensional measure must have a 1D error (eg Symmetrical, Bounds1D).. not a 2D (Ellipse) or 3D (Ellipsoid).
The question of "Angstrom" vs "AU" is a unit-compatibility one, which is outside the scope of this model. We expect the units associated with any given Measure are compatible with the domain, and the client/consumer is responsible for verifying this.