Plot 3D symbols via plot3d in animations (via events)

[PaulWessel]

See this forum post for background. In the design of events we only considered plotting symbols via plot, and then later we added the capability of using meca, coupe, and velo. However, 3D symbols via plot3d were left out.

I think there are various ways we can extend events to handle symbols offered by plot3d. Since plot and plot3d both can accept z-ranges in -R and -p and -JZ as well, it is not enough to check for those options. Furthermore, plot3d expects a z-coordinates as part of its input. Hence, I think we need to tell events that we are selecting from the 3-D symbols in plot3d. Some possibilities:

1. The only unused upper-case letter in event is -I. So it could be used to flag 3-D mode.
2. We could add a modifier to a suitable option to flag this effect.
3. We could let -Z (used for meca etc symbols) flag 3D by giving it no arguments.

I think the last suggestion makes most sense. Z is a better mnemonic than I and it should be simple to just let -Z with no arguments mean two things:

1. Call plot3d instead of plot when doing the plotting (the -S argument etc are passed as string options anyway)
2. Expect an extra input column for the z-coordinate

Let me know what you think of this plan for enhancement.

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[joa-quim]

I think that is ok but it will put more pressure on the ps spheres. 3D scatter plots with flat symbols (except cubes) aren't particularly nice.

[Esteban82]

I agree with -Z.

[PaulWessel]

Yes, we do want those f*ng spheres and eventually ellipsoids.

[PaulWessel]

I am working on a PR for this (events-3D) and will keep hacking away until I can make a short movie of some moving cubes...

[gd-a]

Always too late, but this :

-Se${azimuth}/0.3/$(gmt math -Q 0.3 ${elevation} SIND MUL =)

gives decent "circles" for plot3d (except when azimuth is 0, then it reverts back to ugly ellipses)