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# Bug when trying to create a normal to a face

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### Bug when trying to create a normal to a face

Posted by Richard S. at August 17. 2010

Hello guys,

I hope someone can help me.

I need to compute normals to different faces, but when I try  the measure tool "Normal to a face"

and use it to compute the normal to a sphere at the point at the bottom of it (in z-direction) i get

the error massage: "Normal vector of a face has null magnitude"

The same happens if I write a script and use GetNormal.

The strange thing is, that this only happens if i want a normal in the negative z-direction.

I use version 5.1.3 - so if  someone of u uses the newest version and he could check if this bug has been fixed

that would be nice.

Thank you,

Richard

### Re: Bug when trying to create a normal to a face

Posted by JMB at September 02. 2010

Previously Richard S. wrote:

I use version 5.1.3 - so if  someone of u uses the newest version and he could check if this bug has been fixed that would be nice.

Hello Richard,

I am using 5.1.4 and the problem occurs in both the +ve and -ve directions of Z.  My GUI procedure was:

1. Create a sphere radius 100

2. Explode its face

3. Create 4 vertices at (200,0,0), (0,200,0), (0,0,200) & (0,0,-200)

4. The create normal works for the first 2, but errors on the last two with the message you reported.

If you can post the python script here, I am willing to test it for you in 5.1.4.

Regards,

JMB

### Re: Bug when trying to create a normal to a face

Posted by Richard S. at September 02. 2010

Hello JMB,

you´re right, this problem has nothing to do with the direction. In my particular case i had a radius of 20 i think and the problem was that there is an "edge"  at the point  (0, 0, -20) on the surface of the sphere, which came from approximation of the ideal sphere. This is the same in 5.1.4. The getNormal funktion can´t handle the points on those "edges".

So I tried to approximate the normal at this point by two normals near it.  But this didn´t  work  perfectly, as i don´t know where these "edges are, until i get the error message.

Perhaps you have an idea how to solve that one.

Thanks a lot.

Regards,

Richard

### Re: Bug when trying to create a normal to a face

Posted by JMB at September 02. 2010

Hello Richard,

Try a normal to the point (1,0,200), then it worked for me.

Regards.

### Re: Bug when trying to create a normal to a face

Posted by Erwan ADAM at September 03. 2010

Previously Richard S. wrote:

Hello JMB,

you´re right, this problem has nothing to do with the direction. In my particular case i had a radius of 20 i think and the problem was that there is an "edge"  at the point  (0, 0, -20) on the surface of the sphere, which came from approximation of the ideal sphere. This is the same in 5.1.4. The getNormal funktion can´t handle the points on those "edges".

So I tried to approximate the normal at this point by two normals near it.  But this didn´t  work  perfectly, as i don´t know where these "edges are, until i get the error message.

Perhaps you have an idea how to solve that one.

Thanks a lot.

Regards,

Richard

This bug is present in development version too ... we are going to see how to fix it for next version. Regards, Erwan.

### Re: Bug when trying to create a normal to a face

Posted by Erwan ADAM at December 23. 2010

Previously Erwan ADAM wrote:

Previously Richard S. wrote:

Hello JMB,

you´re right, this problem has nothing to do with the direction. In my particular case i had a radius of 20 i think and the problem was that there is an "edge"  at the point  (0, 0, -20) on the surface of the sphere, which came from approximation of the ideal sphere. This is the same in 5.1.4. The getNormal funktion can´t handle the points on those "edges".

So I tried to approximate the normal at this point by two normals near it.  But this didn´t  work  perfectly, as i don´t know where these "edges are, until i get the error message.

Perhaps you have an idea how to solve that one.

Thanks a lot.

Regards,

Richard

This bug is present in development version too ... we are going to see how to fix it for next version. Regards, Erwan.

Fixed in 5.1.5

### Re: Bug when trying to create a normal to a face

Posted by Richard S. at December 24. 2010

Hello Erwan,

thanks for the great work!

Just for curiosity I´m interested in the way you solved the problem, perhaps you could give me an impression of how you fixed it.

Now I have another problem:

The make-common algorithm seems to  need an improvement too.

First problem is the execution time which seems to be very long (compared to the other boolean operations). I wrote a tui script which needs to execute a lot of make-common operations and  sometimes one operation takes several seconds, which is way to slow to make the script usable.

Secondly, I often get an error message that says the operation can`t be done on the given shapes. most of the time this occurs if I try to do the operation on a small solid like a sphere and a big face.

Hopefully this could be fixed as fast as the last one!

Best regards,

Richard

### Re: Bug when trying to create a normal to a face

Posted by Richard S. at January 12. 2011

Is there any enhancement planned for the make-common algorithm?

Regards,

Richard

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Activate by Richard S. on Aug 17, 2010 05:47 PM