Posted: 07 March 2007 at 2:32pm | IP Logged

Hi All. 

I came across some info which I thought may be benificial to anybody who surfaces quite a bit so I thiough I'd post it here.. below is the original question and followingis the responce I got from PTC.

Cheers,

James

Original Question..

I have a few questions about surface normals and the effect that they can have.

Firstly, What defines the normal direction of a surface (swept, extruded and blended if possible)? E.g. what defines the initial direction of a surface offset – I’m assuming it’s the normal direction….

Secondly, Is there anything that can be done which would change the normal direction of a surface without using edit / flip normal?  For example, is there anything that can be done to a blended surface (redefining curves, changing tangency conditions etc) which would cause the normal to change?

Thirdly, if you have two adjacent surfaces, both of who’s normals are opposite to each other, and they are merged does the resulting quilt have a normal which matches the primary quilt?

I’d also like to know what else surface normals can effect – here’s a few which I’ve come across.

The image below shows a blended surface in grey, an extruded surface in yellow, an intersect in red, a sweep in green and a point on the end (not a ratio) of one of the segments of the intersect.  

Posted: 07 March 2007 at 2:36pm | IP Logged

Here is the responce from Tim and Paul at PTC.

James,

In answer to your question there are a number of elements which define a surface normal.  

For example when sketching a line the normal is taken from the direction ofthe line creation (i.e left to right or right to left.)  In the case of anarc the direction is taken counter clockwise. 

The normal is to the left of the curve direction. 

There are further elements which can overwrite these such as an extrude where the surface normals will be defined from the direction. 

You are correct the initial direction of an offset is defined by its surface normal. 

The normals for a boundary blend are taken from the first curve used to define the blend. Therefore you could change the curve order and this could change the surface normal.

You are correct about the surface merge. The normal for the quilt is taken from the primary surface. 

Hopefully this will give you some answers to your questions 

Regards 

Paul.

____________________________________________________________ ___

I've attached a part to demo what I've been talking about

Cheers,

James

2007-03-07_143544_surf_normal_test.prt.zip

Posted: 07 March 2007 at 2:37pm | IP Logged

If anybody has any more information or experience in dealing with this I'd love to hear about it!

Cheers,

James

Posted: 12 March 2007 at 3:08pm | IP Logged

You are trying to get a surface to sweep relative to the pull direction.  (needed if you are using a sweep instead of draft)     

SURFACE NORMAL:   A surface normal is a line perpendicular to a line (at a point) that is tangent to a curve or surface at a point.   Basicly a take on the first theorem of Calculus.

Oh.. I forgot to say hi James.   We got 60 degree weather in Chicago today.   Bet is is raining in england. ;)

Posted: 12 March 2007 at 3:58pm | IP Logged

Hi Bart, well yes it is raining! (in Ireland I might add ) and I have a cold and I feel miserable!  but hey, colds pass, you come to enjoy the rain and I'm still left in this beautiful country sourounded by Guinness!  Happy almost Paddys Day!

I think what yo've described is surface normal at a point - lime a porqupine analysis of a surface, however, ProE also has it's own definition of a surface normal - and it's very dependant on quite a few things (dependong on how your surface was created! which I found a little confusing!

Anyway - though the info may be of use to somebody! :)

Good talking to you again Bart!

Cheers,

James

p.s. how's everything at Design Engine? see you at User this year?