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Reversed Normals When Importing DAE & OBJ from Rhino

VeronicaAnderson

What can I do to make sure that I don't have reversed normals before exporting/importing a bunch of geometry into CityEngine from Rhino? All the surfaces I created were basically done the same way and I'm not sure why they are coming into CityEngine all randomly backwards. Actually, I'm sure it's not random, but it's frustrating and a waste of time and I'd like to understand why this happens and what I can do about it. I've attached the offending files in DAE, OBJ and Rhino format, for your convenience.

patios.obj.zip

Patios.dae.zip

patios.mtl.zip

Transportation Center.3dm.zip

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Accepted answers

Anonymous User

I use the same process, from Rhino to CE - both 2D surfaces, and 3D models with textures - and I get the same problems.

Usually I'm bringing in 2D surfaces drawn from plan view. When I see many facing down and many facing up, then I write a rule like this:

Shape --> extrude(100)

Applied to those shapes the extrusion will either go down or up, then I select the down facing shapes from the side view so as to only select the shapes with reversed normals. You might have to cut and paste those shapes to another layer depending on which CE version you are on (and then select them by layer). Main idea is after you have all of those shapes selected, then in shapes menu do "Reverse Normals" ( and then put them back on correct layer if you had to change their layer). For small imports (<20 objects reversed maybe), then just hold shift while selecting each shape.

For 3D models, I just go back to the original Rhino model, and use Flip to reverseNormals, then export again replacing the current model (be sure to refresh the folder in CE containing the model). I think that Rhino's Dir is also for that, but gives more options. Try both and see which is best.

Also, to see which faces on your models have normal problems, use the gear icon above the viewport, and turn on "Backface Culling" this will show the faces as transparent if you are behind them. This is how the WebScene view displays models, so if you are exporting to web scene, then it is best to turn this on and check over your model before exporting.

Chris

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ChandrasekharreddyGuda

Thank u Thomas Fuchs, i will try above

ThomasFuchs

chandrasekhar reddy guda wrote:
Matthias Buehler
i am also having the same problem, normals problems getting when importing drawing file, please share a code of .net

Hello Chandra Sekhar Reddy Guda,

There is no need to write .net code, in fact CityEngine does not use .net at all.

Instead you can use CityEngine CGA modelling language to manipulate the imported shapes from a drawing file.

The cga rule snipped above provided by Matthias Buehler can be used to reverse any down facing normals.

Further information can be found in the CityEngine CGA Help:

reverseNormals Operation

As a second option, you can use the CityEngine python scripting interface.

This python script corrects the shapes normals after import:

# checks if the shape point order is clockwise

# note: applies to horizontal plane (x: east, y: up, z: south)

def clockwise(shape):

shapeVertices = ce.getVertices(shape)

sum = 0

for i in xrange(0,len(shapeVertices),3):

x1 = shapeVertices

z1 = shapeVertices[i+2]

x2 = shapeVertices[(i+3)%len(shapeVertices)]

z2 = shapeVertices[(i+5)%len(shapeVertices)]

sum += (x2-x1)*(z2+z1)

return sum < 0

if __name__ == '__main__':

selectedShapes = ce.selection()

for shape in selectedShapes:

if ce.isShape(shape):

# ensure counter-clockwise order of input shapes (normal up)

if clockwise(shape):

ce.reverseNormals(shape)

Further information can be found in the CityEngine Python Help:

Python Scripting Interface Reference

ChandrasekharreddyGuda

Matthias Buehler

i am also having the same problem, normals problems getting when importing drawing file, please share a code of .net

MatthiasBuehler

There we go ..

normalYComponent = convert(y, scope, world, orient, 0, 1, 0) - convert(y, scope, world, orient, 0, 0, 0) # calc scope normal's y component in world coords

Shape -->

alignScopeToAxes(y)

ShapeAligned

ShapeAligned -->

case normalYComponent >= 0: # if positive: ok, otherwise reverse normals !

TestMove

else:

reverseNormals

TestMove

TestMove -->

t(0,1,0)

Matthias Buehler

Head of 3D Technologies

twitter: @MattB3D

--------------------------------------

Garsdale Design Limited

matthias.buehler@garsdaledesign.co.uk

www.garsdaledesign.co.uk

VeronicaAnderson

Hey Matt,

That would be a good code to have if you are willing to share please post!

-V

MatthiasBuehler

Hey,

Yes, the vertex order drives the normal direction.

Btw. you can write a rule that automatically fixes the orientation if needed.

Let me know if yo need the code.

Matt

Matthias Buehler

Head of 3D Technologies

twitter: @MattB3D

-------------------------------------

Garsdale Design Limited

matthias.buehler@garsdaledesign.co.uk

www.garsdaledesign.co.uk

BenLeslie1

Sounds like you have a solution so just a thought:- I wonder if the orietation of the faces is linked to the direction the polygons were originally drawn

e.g. clockwise polygons face-up

anti-clockwise polygons face-down...... or visa versa

.......just a thought..........

VeronicaAnderson

Me too. I've never used 3dsMax so I'm not 100% informed on this, but to me CE & Rhino are like the power couple of the 3d modeling world. If only Rhino could get some geolocation capabilities going then life would be perfect.

Anonymous User

No problem. I like using Rhino with CityEngine.

Chris

VeronicaAnderson

Yay, Chris!

I'll use Dir before exporting from Rhino from now on to check my geometries and eliminate some unnecessary back and forth. Thanks for saving the day!

Cheers,
V

Anonymous User

I use the same process, from Rhino to CE - both 2D surfaces, and 3D models with textures - and I get the same problems.

Usually I'm bringing in 2D surfaces drawn from plan view. When I see many facing down and many facing up, then I write a rule like this:

Shape --> extrude(100)

Chris

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