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Boundary variables for auxiliary coordinates of more than two dimensions #527
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Dear all I propose the following changes to remedy the defect described above in Sect 7.1 "Cell boundaries". In addition I propose to insert some new subsection headings, explanatory text, and rearrangement of text in Sect 7.1, to improve clarity. I don't believe this is any change to the meaning of the convention, except for one small generalisation (at the end). On account of that, and because the text changes are quite extensive, I've relabelled the issue as an enhancement. The proposed changes are listed below. You might find it easier to look at the pull request or the HTML of the modified document. Cheers Jonathan
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This is a small generalisation to admit the possibility of 2D cells in other than the horizontal plane e.g. in (height,latitude). I'm sure CF is being applied to those cases, and they might need 2D auxiliary coordinates. I haven't made the requirement for the vertices to be traversed in a right-handed way apply to cases apart from the horizontal plane, where we already have that requirement. |
Section 7.1 on "Cell boundaries" contains the following text, about providing boundary variables for auxiliary coordinate variables of more than two dimensions:
There is no example given. I suppose it must mean something like this for three dimensions:
Since it talks about traversing the vertices clockwise in the lat-lon plane, it must be concerned with horizontal faces of the 3D cells. A horizontal coordinate variable only has to be 3D (rather than 2D) if the cells aren't aligned in vertical columns. Do you agree with this interpretation? If so, we should clarify it. 3D cells don't just have horizontal faces, so this convention is of restricted use. For a more general treatment of bounds in two dimensions, we could refer to UGRID.
Cheers, Jonathan
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