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Shortest distance across irregular surface

14 REPLIES 14
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Message 1 of 15
Cnoj
1882 Views, 14 Replies

Shortest distance across irregular surface

Quite often I need to measure shortest surface distance between two points (electrical tracking diatance) as in pic below. I can do it iteratively by taking a range of slices out of the part (2nd pic) and measuring the cut edge length but it's quite meticulous and time consuming. Anyone have a better/easier/faster way to do this? .ipt attached.

Thanks,

Jon.

 

2012-11-19 09_49_59-Autodesk Inventor 2010 - [Part2.png

 

2012-11-19 10_11_27-Autodesk Inventor 2010 - [surface distance.png

Inventor 2013/Pro SP2
SimCFD 2015 SP2
Win7-64bit
14 REPLIES 14
Message 2 of 15
JDMather
in reply to: Cnoj

I get error that file not checked out to me, but -

 

Not sure what the red and green cylinders are for.

Create axis through surface at desired point.

Create workpoint at intersection of surface and axis.

You can now measure distance between these workpoints.


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Message 3 of 15
Cnoj
in reply to: JDMather

Does the check-out error stop you from opening the file? I just use Save As to remove check-out flags if I can open them.

 

The red/blue cylinders are the points I'm trying to measure between. If they were electrical terminals at high PD then electricity would 'track' across the surface taking the shortest path betwen terminals.

 

I don't fully understand your solution but it sounds like it would measure a straight line distance. I need the length of a curvy path following the surface.

 

Also I should add that my cutting solution from first post isnt ideal as it can only find paths that stay on a single plane, which won't always be the case.

 

If you can open my model and move the EOP down you should see my single plane attempt.

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Message 4 of 15
JDMather
in reply to: Cnoj


@Cnoj wrote:

 

If you can open my model and move the EOP down you should see my single plane attempt.


I can open the file just fine.  There is nothing below the EOP in the file you attached - so I didn't understand what you were trying to do.  I thought you were after a straight line distance.


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Message 5 of 15
Cnoj
in reply to: JDMather

Sorry about that. Here's the correct part file.

 

WP3_offset param adjusts the angle of the 'measurement cut' which I'm using to get an edge to measure the length of.

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Message 6 of 15
Cnoj
in reply to: Cnoj

Here's another one. Pretty obvious that the shortest surface path from red to blue will not lie on a single plane.

 

Any ideas how you could plot/measure it?

 

surfdist2.png

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Message 7 of 15
sam_m
in reply to: Cnoj

if it's an obviouse "as the crow flies" straight line between 2 points along/around an object then could offset a plane above the points, create a 2d sketch with a line joining the 2 points, then 3d-sketch and intersect that line with the object to give you the creepage-path along the surface.  Use measure loop to get the length.

 

But... if it's something like the 2nd example where the shortest path isn't necessarily obvious (presumably direct to the "finger" and then around it instead of over the top) then i think you'll need to be creative and draw the expected path on the 2d sketch before intersecting in the 3d sketch.  Can't think of an obvious "minimum distance between 2 points but following a surface" which is what I believe you're after.

 

However it's done it's going to be an approximation as there's probably too many variables in the real-world which would affect the creepage-path (surface contamination/humidity/etc.)



Sam M.
Inventor and Showcase monkey

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Message 8 of 15
LT.Rusty
in reply to: sam_m

Create plane, project cut edges, measure loop?

Rusty

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Message 9 of 15
Cnoj
in reply to: sam_m

"Can't think of an obvious "minimum distance between 2 points but following a surface" which is what I believe you're after."

 

That's exactly what I'm after, Sam_m. I'm not at all worried about real world stuff, just cad world for now 🙂

 

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Message 10 of 15
sam_m
in reply to: LT.Rusty

Rusty, it's not a simple cut with a plane tho.

 

Look at the cylinder with a finger example picture - a straightforward cut would cut the finger in half and provide a "shortest path" going up and over the finger (red path in drawing)

 

But, if you were an ant wallking from the red to blue points you'd walk in a straight line to the finger, to a point tangential with the path, then around nearly 1/2 the finger's circumference, to a point tangential to the straight-line to the blue-point - isn't that the shortest path? (green path)

 

original1.jpg

 

 (sorry for crude quick drawing - hope it makes sense...)

 

 



Sam M.
Inventor and Showcase monkey

Please mark this response as "Accept as Solution" if it answers your question...
If you have found any post to be helpful, even if it's not a direct solution, then please provide that author kudos - spread that love 😄

Message 11 of 15
Cnoj
in reply to: sam_m

I like the ant anology.

Green path is obviously shorter but wouldnt be shorter still to head for a tangent to the finger rather than heading for it's center then skirting round?

 

So the question is: How to answer the above question 🙂

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Message 12 of 15
Cnoj
in reply to: Cnoj

Here's another one.

Shortest distance will lie on a single plane for this one but I still don't see a way of finding it without iterating/homing in on the plane manually (or mathematically in this simple case).

 

surfdist3.png

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Message 13 of 15
Maxim-CADman77
in reply to: Cnoj
Message 14 of 15
hosford
in reply to: sam_m

If you do a google search on "shortest path on a polyhedral surface" you will find this is a pretty hot topic.

A thought is if it doesn't have to be precise, you could apply a surface texture of squares or circles and visually assess the path.

Thaddeus Hosford
NUC9i9QNX i9-9980HK, Win 10 Pro 64
Nvidia GTX 1650
Inventor 2021
Message 15 of 15
graemev
in reply to: Cnoj

Two solutions, one per problem.

 

How accurate a solution would you like?

 

The first returns fairly stable three decimal consistency across a somewhat generous variation in slice angle.

 

The second is generated by a slicing plane through the "finger's" lower fillet center point, as plotted in Sketch 4, measured 45° from the upper disk face. (Which should yield something close to the shortest path over the fillet.) The planar "bee line" from post to fillet path may not be mathematically the shortest, but would be a close approximation.

 

(IV2015 SP2)

 

The more complicated the geometry, the more complicated the solution, of course. Visualizing a string pulled taught between points, though constrained to the surfaces, is a good way to home in on a simplified result. (Example: Two points on a cylinder: a helix about the shorter polar angle. If by chance the points are coplanar with the cylinder's axis, the helix has an infinite pitch.)

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