CUBE vs. Sphere

gomi42 · April 21, 2021 at 9:27 AM

From time to time I revisit my processes and self-made tools that create the XML and the tiles to keep them up-to-date. Since ever I have been converting the equirectangular image to cubes and then the cubes to tiles. For multiple resolutions of course. The following question has been asked a decade ago but I don't find a more recent one: Is this still the state of the art?

I don't mind converting to cubes first, but I'm wondering if using a sphere instead would be fine as well (plus split the sphere into tiles). Is there an advantage for one or the other way? Which one creates the best results, sphere or cubes?

Michael

odysseyjason · April 22, 2021 at 4:14 AM

Multiresolution CUBE is the most efficient projection in tile and data usage for full spherical imagery that is currently supported by krpano. Beyond 60 degrees latitude at the poles the spherical format starts to get quite wasteful (from 50% to 100% wasteful from 60 degrees to 90 degrees). The spherical format is best for partial panoramas, especially if they do not include much above or below 60 degrees latitudes. Technically, the percent waste is a 1- ( COS(angle above or below horizon)). A truly state of the art projection would be the spherical projection from -60 to +60 and a flat top and bottom multiresolution square projection of what is above 60 degrees (it would be a circle projected onto the square) as even the cube gets less efficient towards the corners. I don't know if this projection exists but would be happy to take credit and name it.

gomi42 · April 22, 2021 at 7:43 AM

Thx a lot. I see I'm still on the right track and keep preferring Cubes over Spheres for full spherical images.

klaus.krpano · April 24, 2021 at 8:18 PM

Hi,

right, good explanation by odysseyjason!

As always there are advantages and disadvantages, e.g.
- the advantage of using spherical would be one less conversion step
- but therefore the more tiles would need to be loaded to fully render the pole areas

That means for smaller 360x180 panos that don't have many tiles using spherical can be a consideration.
Or for panos that will be rarely viewed (or even zoomed-in) at the pole areas.

Just test a few panos with cube-conversion and without. For doing that e.g. just change the 'converttocube=true' setting in the vtour-multires.config.

Best regards,
Klaus

venca.venca · December 13, 2022 at 3:43 PM

Quote from klaus.krpano

Just test a few panos with cube-conversion and without. For doing that e.g. just change the 'converttocube=true' setting in the vtour-multires.config.

Klaus, is there any rationale behind the "converttocubemaxwidth =60000" https://krpano.com/docu/tools/config/#converttocubemaxwidth I mean the default value 60000px? And are there any limits for "converttocubemaxwidth"? I often work with high resolutions (360x180) above 60000 so I adjusted converttocubemaxwidth to my values in order to get cubes. Is it OK to have it set this to 300000 (as a limit for *.psb resolution)? Now it's working fine for me with 300000 set, but just after the change of the converttocubemaxwidth in the config files I got few error messages in MakeVTour and that made me wonder if there are any limits. Thx

Venca

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