Positive vertex data appears in negative unity space

Hello there,
.
i am loading my 3d models into unity. Small assets are of course centered around 0,0,0. But i have level models that are not centered around 0,0,0.
I nailed it down to the following problem:

I have a *.obj file in wich I only have positive x and z vertex values:

v 1.500000 -0.500000 1.500000
v 1.500000 0.500000 1.500000
v 1.500000 -0.500000 2.500000
v 1.500000 0.500000 2.500000

If i now open this file in unity the model (cube) get visible in the negative section of unitys coordinate sysetm. If i place the camera at the location ( 1.5 , 0 , 1.5 ) were the cube should be, you see the difference.
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alt text
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Can someone please tell me what i need to do to see a positive vertex from a obj file in the positive part of unitys coord system?
I have hundrets of models i would need to chnage otherwise … and the game logic as well. ( game was prev. coded in custom java code)
.
thank you in advance!

Most file formats use a right handed coordinate system. Unity uses a left handed system. So whatever your coordinates are in your original source, if they are specified in a right handed system, they need to be converted to a left handed system which makes it necessary to invert one axis. How you map from one system to the other is kinda arbitrary. Not every coordinate system uses the x-z plane as the ground and y as up. So there’s almost always some sort of conversion going on.

OBJ does not necessarily contain right or left handed data. That’s completely up to the exporter. Also the winding of the faces may also differ from system to system. In Unity a clockwise winding indicates the front face. That does not necessarily be the case for your model. Some OBJ models even assume double sided meshes and do not pay any attention to the winding order which is generally an issue when importing such a model.

Hi there,

and thanks for your answer.
I knew about the left hand and the right hand system stuff.
But my knowlege is limited here.
.
If i have only positive values in my obj file ( handwritten, no exporting tool at all ), i would expect the object to appera at this positiv position in any matrix system. dont you think ?
.

So this is why i expect this *.obj data to be at POSITIV ( 1.5 , … , 1.5 ) … but its not.

v 1.500000 -0.500000 1.500000
v 1.500000 0.500000 1.500000
v 1.500000 -0.500000 2.500000
v 1.500000 0.500000 2.500000

Any think i overlook here ?

thanks
kai