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Data in exported shapepack for ellipsoids

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asked Mar 30 by MaxWiebicke (220 points)
Hi,

I was just wondering, how the data of ellipsoids is saved when exporting it  with

sp=ShapePack()
sp.fromDem(S,S.dem)
sp.saveTxt('....')

I understand the following entries in the output file:

Label Shape Center[x,y,z] missing_value orientation_vector[x,y,z] semiaxes[a,b,c]

The value I called missing_value corresponds to the first semiaxis -- why?. Should the missing_value be the angle for the orientation_vector? As described in the Quaternion?

Best regards, Max

1 Answer

+1 vote
answered Mar 30 by eudoxos (44,890 points)
selected Mar 31 by MaxWiebicke
 
Best answer
Hi Max,

the missing_value is bounding sphere radius, so the maximum semi-axis in case of ellipsoid. It is not necessary to reconstruct the ellipsoid, as orientation is stored as rotation vector (which is unit-length rotation axis times the angle of rotation), but it is used by RawShape https://woodem.org/woo.dem.html#woo.dem.RawShape.radius so that it can represent any shape by its bounding sphere.

I hope this answers your question. I am glad there are curious people out there :))

Best, Vaclav
commented Mar 31 by MaxWiebicke (220 points)

Hi Vaclav,

thank you for your very fast answer!
That's a great way to store the orientation -- I was already wondering why it's norm was not == 1, but that makes sense.

Best, Max

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