Filter projections in the Change Projection dialog

Discussion of things we want in Geocart
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Bernhard Jenny
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Joined: Thu Mar 22, 2012 5:22 pm

Filter projections in the Change Projection dialog

Post by Bernhard Jenny »

A filter for restricting the projections that are displayed or selectable in the Change Projection dialog would be useful. The filtering could be based on distortion characteristics and other properties. Possible inclusion/exclusion criteria could be:
  • Extent of the area displayed: entire sphere or a section
  • Distortion: equal-area, conformal, compromise, equidistant
  • Shape of the projection outline (for world map projections): pole lines, ellipsoidal, spherical, interrupted, asymmetric, sinusoidal antimeridian, height-to-width ration
Bernie Jenny
RMIT University, Melbourne
daan
Site Admin
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Joined: Sat Mar 28, 2009 11:17 pm

Re: Filter projections in the Change Projection dialog

Post by daan »

Bernie, interesting idea!

“Interrupted” is a (largely) independent trait. Maybe “interruptible” could work as a filter element.

Could you explain “sinoisoidal antimeridian”?

In “shape of the projection outline” do “spherical” and “ellipsoidal” refer to the datum? (In which case, I would answer that any projection could be set to spherical or ellipsoidal datums.)

Thanks!
— daan
Bernhard Jenny
Posts: 12
Joined: Thu Mar 22, 2012 5:22 pm

Re: Filter projections in the Change Projection dialog

Post by Bernhard Jenny »

Hi daan,

Ellipsoidal should have been elliptical (e.g., Mollweide), and spherical should have been globular.

As for "sinusoidal (anti-)meridian", I was thinking of Bojan Savric's distinction between elliptical and sinusoidal shapes for meridian lines in his study "User preferences for world map projections".

A criteria to add could be straight vs. curved parallels.

Also, could the Change Projection dialog be resizable?

Bernie

PS - why are the Ginzburg VIII, Denoyer, lateral equidistant, and Ortelius oval projections in the Miscellaneous group and not the Pseudocylindric group?

PS 2 - what is the lateral equidistant?
daan
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Re: Filter projections in the Change Projection dialog

Post by daan »

Hello Bernie, and thanks for the explanations. I think I understand all of those now.

Ginzburg VIII, Denoyer, lateral equidistant, and Ortelius oval are not proper pseudocylindrics. That is, the x coordinate is not strictly proportional to the longitude along a given parallel.

Lateral equidistant preserves distances from the central meridian at any parallel to any point along that same parallel.

Best,
— daan
Bernhard Jenny
Posts: 12
Joined: Thu Mar 22, 2012 5:22 pm

Re: Filter projections in the Change Projection dialog

Post by Bernhard Jenny »

Hi daan,

Thanks for the explanation concerning Ginzburg VIII, etc. As a side note, it seems that John Snyder distinguishes true pseudocylindricals from "regular" pseudocylindricals (Flattening the Earth, 1993, page 189).

Bernie
daan
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Re: Filter projections in the Change Projection dialog

Post by daan »

Interesting interpretation, Bernie. I do not interpret Snyder’s verbiage there as attempting to distinguish “true” pseudocylindrics from “regular”. There is no support in the rest of the literature for such a distinction. I think he is just emphasizing that some projections casually appear to be pseudocylindric, but actually are not.

Best,
— daan
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