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Lets say i want to flip a set of 3d polyhedra. Lets say Flip Y.
Instead of some complex voodo involved wouldn't one just rotate by 180 degrees around X axis? Will this provide same result as standsrd flip, because i have no idea how to flip a set of objects...
Not sure what the standard flip is but my gut feeling (and I could be wrong) is you want to scale Y by -1. Rotating can never actually change an object, just it's orientation.
It's more kind the other way around: You can express any rotation of a vector by reflecting it about a given plane (this is why quaternions store the cosine of just one half of the rotation angle). With reflection i mean flipping or mirroring not sure which term is right.
So you can also flip that single vector by rotation and you're not so wrong.
But for a whole model with multiple points the difference between flip and rotation shows up. Usually you negate one (or two) axis to flip the model.
1 hour ago, Gnollrunner said:Not sure what the standard flip is but my gut feeling (and I could be wrong) is you want to scale Y by -1. Rotating can never actually change an object, just it's orientation.
That is more of a mirror than a flip. But it will flip the normals. 
2 hours ago, fleabay said:That is more of a mirror than a flip. But it will flip the normals.
True, That is why 3D software usually have a "recalculate normals" option. A simple trick would be to mirror it and to invert the normal in the same direction.
As you say it seems that i need to use a mirror term, ok so lets say i want to mirror Y,
Now i do sth like this:
Calculate geometric center of a shape that consist of x objects
through all selected objects i negate y coordinate of each vertex v.y = -v.y;
Then i calculate geometric center of this shape and calculate a vector from new center to old center - then i translate new shape, however this doesnt fit, shape moves around instead of being in one place this is what i want to fix.
In 1 you see which object i want to mirror
In 2 you see the result
In 3 is what i want to achieve
This must be something simple like some one easy subtraction of a vector however cant see this for now.
In this case I would think that you would just want to take the average of Y min and Y max for the object you are flipping, and flip around that line. For instance you could translate all points in said object by subtracting (YMax + YMin) / 2.0, and then go ahead and do your v.y = -v.y and and then translate back the other way by adding (YMax+ YMin) / 2.0.
