Best fit lines & arcs

[SW]

I've got a load of data point coordinates for measurements around the edge of a flat component. I need to create best-fit lines and arcs based on these data points, ideally within Pro/E. I can bring the data in as datum points, and probably can get a .pnt file too, but don't know an easy way of creating the best-fit lines.

I thought re-style would be the best bet, but I need facet data to create analytical features.


The CMM module can create best-fit lines, but I don't have an
as-designed reference part to start with and after a quick look at the module work-flow, it doesn't seem to be a good
approach, even if it is possible.

Has anyone got any other suggestions on how I can do this?

Many thanks,

Sam

 

[cloughna]

I am a little unclear on your problem, but as I understand it, this is what I would do.

Take my huge load of datapoints, put them into excel, and get a best fit line (poly, linear, whatever). Copy the equation of that line and create a datum curve based on that equation.

Depending on the situation, you might also want to checkout the trajpar and evalgraph functions

 

[SW]

It sounds like you've got the idea of what I'm trying to achieve. I could do it in Excel, its just I've got quite a few line segments, so I wanted to jut select the relevant points within Pro/E and put a best fit line through them.

 

[rklatte]

Check this video tip from Leo Greene:

http://e-cognition.net/Pages/Surf-Model-1.html

Basically just get the data points into a .ibl file (text file with a certain syntax) and create a curve using the "From
File" option. You will the option to simplify the curve too (see the video tip).

 

[cloughna]

Is this data set of points defining a line, or is at a point cloud from which you want to interpolate a line-of-best-fit?

 

[design-engine]

restyle will manage facet data too....

I could talk for a week about reverse engineering parts using point cloud ... then creating parametric data to those points....


[url]http://www.proetools.com/courses/pro_surface/advanced_import .htm[/url]


http://www.proetools.com/courses/pro_surface/restyle.htm

On link discusses capturing point cloud data into a 3d model and the other does the same yet creates parametric data native to Pro/ENGINEER. Big difference

I met leo at the Caralinas PTCUSER conference. Great Guy!
Edited by: design-engine

 

[SW]

I've created a manual approximation of what I'm trying to do.

The image below shows a set of points where I have manually put very poor approximate best fit lines through the points. I want to be able to do the line fitting automatically, as you would do in Excel using the linear regression capabilities. If I could just do this with straight lines it would be good.



Hopefully this makes sense.

Sam


Edited by: SW

 

[SW]

I've just found that AutoCAD Civil can do it, as explained on page 43-45 in Probert et al "Mastering AutoCAD Civil 3D 2008"

Is there any way of doing something similar in Pro/E?

Sam

 

[design-engine]

nothing beats your eye and a comb plot tool... besides the data you get from camera or scanner is always above and below the average mean. My model will be parametric and in between the highs and the lows.All the reverse engineering tools such as restyle, geomagic will preform the tasks you looking for.

 

[SW]

I often use Restyle to work with 3D point clouds to create facet data and then surfaces, but how can I use the module to create best-fit lines and arcs from an array of 2D (or 3D) data points?

I need to use the least squares method, or an equivalent, for some simple regression within Pro/E. The maths isn't difficult and I've found some AutoLISP code to do it, but I've no idea how to do the same thing in Pro/E.

Sam

Edited by: SW

 

[SW]

This shouldn't be that difficult, I need to read the coordinates of the points relative to pre-defined coordinate system, perform some simple calculations using this data then create a datum curve relative based on the results of the calculations. Is there a straightforward way to do this sort of thing in Pro/E? Do I need to use Pro/toolkit or J-link?

Sam

 

[drwtds]

I've created a manual approximation of what I'm trying to do.

The image below shows a set of points where I have manually put very poor approximate best fit lines through the points.

I tend to create spline or curve through all points. Then I check the curvature plot and try to simplify spline into single segments. So it ends up with a couple of sketches which contain single spline.

I do not care about curvature transition between, only tangent.

In the end I combine them all within Composite(Approximate) Curve, and Pro/E dos the whole job of curvature transition for me.
The quility is up to discussion but it works.

However it all works fine until there is a situation with "spine" curves(Boundary Blend) wich approximate curve should follow. I find i difficult to create cute curves through 3 points, becasue Pro/E turn off control polygon for them.

Has any one over came this problem?