Author Topic: Ah ha!  (Read 280 times)

M.E.

  • Newbie
  • *
  • Posts: 13
Ah ha!
« on: March 21, 2018, 10:09:22 PM »
Ah ha! In another post I explained a problem I have with passing drawings on to be plasma cut for to build boats (skiffs, actually). It's been driving me nuts. The cutter has the latest, greatest AutoCad (which I cannot, nor ever will throw the coin down for) and he relays the hitches in my drawings to me. I know through research that AC has a function to both identify and 'fix' those problems but that is both time consuming for him and unacceptable to me for obvious reasons. So, I began to study and going through my work procedures and found at least ONE of the main culprits:

I import into DC lines from a surface modeling program specific to boats called ProSurf. It has the ability to take 3D shapes and lay them flat in order to be cut on a plasma, router or other methods cutting table. These imported lines, even if they are staight are comprised of MANY points; it's the nature of the program to do so.

In order to be economical with material use, I need to chop up some of these generated shapes to achieve that. For example, a skiff can have long curved elements such as sheer/chine 'flats' and other lengthy longitudinal scantlings that because of their curvature would eat up a lot of expensive real estate if not parsed.

I discovered, by experimenting with the 'combine lines' command that these chopped up parts did not have joined ends to lines where the were sliced. To be specific: If I took one of these shapes and bisected it with a line, then, after making copies used 'section trim' command to make  two pieces of it I would then use the 'trim' command to remove the tails. BUT! after zooming in at these trims a bazillion percent, sure enough, they did not come clean - there are gaps. Thereafter by using the 'point select' command I'm able to heal them. I prefer that to 'join end points' because I don't know why!

I suspect this problem has to do with the numerous points generated by the parent program.
Anyway, I haven't sent off the lastest set of drawings so, we'll see...

What are the chances of DC having a function to detect these gaps?   

bdeck

  • Hero Member
  • *****
  • Posts: 896
Re: Ah ha!
« Reply #1 on: March 22, 2018, 01:09:21 AM »
If you are trimming Curve entities, DC cannot slice precisely. The iterative interpolation routine used for trimming curves seems to have been written in the 1980s, and optimized for speed, not accuracy.  If that is the problem you are having, there is no precise solution unless you write your own. A few years ago DC added one extra iteration to the routine.

If you are trimming Line entities, on the other hand,  the trim will be precise to the mathematical limits of the program. 

For a faster trim without gaps, you could Vector Convert prior to the cut, and then convert Line To Curve afterward. Or just leave the shape as a multi point line entity. If converting back to curves, make certain to add an extra point to each corner in point select mode.

But this method may not be as accurate as your present method, even if the trim line goes through two existing points on the curve.
« Last Edit: March 22, 2018, 01:17:41 AM by bdeck »

Dr PR

  • Hero Member
  • *****
  • Posts: 5614
Re: Ah ha!
« Reply #2 on: March 22, 2018, 09:33:23 AM »
Be cautious when using the functions to cut and combine lines and curves. DesignCAD has a habit of changing a simple line or curve into bazillions of points. In the past the huge number of points would overwhelm some other program a file was being exported to - I don't recall which program.

There are functions to reduce the point count, but these can also change the shape of lines and curves.

I have found that it is much easier and faster to use existing lines and curves as templates, and start over on a new layer and draw new lines and curves by tracing (gravity snap) over the original lines. Then I can make the desired edits while I am drawing the new objects.

Phil
DesignCAD user since 1987

M.E.

  • Newbie
  • *
  • Posts: 13
Re: Ah ha!
« Reply #3 on: March 22, 2018, 12:36:57 PM »
Thanks Phil and bdeck, I just got word from my cutter that he is thrilled with the 'new' work product. He's CNC software digested the test drawings without a single snicker.

I cannot use the point reduction edit because the original surface modeling software matches point-to-point along the edges of NURBS. I don't want to even consider what might happen should I monkey with that monkey! 

"I have found that it is much easier and faster to use existing lines and curves as templates, and start over on a new layer and draw new lines and curves by tracing (gravity snap) over the original lines. Then I can make the desired edits while I am drawing the new objects."

Phil, I don't understand exactly what you are describing above. The principal parts (sides, bottom) produced by the surface modeling program have hundreds of points when imported without any further manipulations. When I 'combine lines' in the original, nothing is added or subtracted as far as I can tell. It seems that the slicing, dicing and addition was the progenitor of all my problems.

Thanks again, you folks are terrific!

Mark

M.E.

  • Newbie
  • *
  • Posts: 13
Re: Ah ha!
« Reply #4 on: October 12, 2018, 02:24:29 PM »
I have to add to this thread because the original problem krept back into the design stream. After much experimenting with various commands and submitting trials to a blessedly willing cutter, I discovered that by doing the following my drawings 'dropped right into' their Hypertherm nesting/toolpath software:

a) Select all principal lines in what needs to have closed geometry and use 'Combine Lines' command.

b) Select all (ctl+a, every drawing on one layer) and then use 'Vector Covert' command. If I need a different treatment as, for example, a set of lines to be markings (layout lines, text) instead of cuttings I make them a different color and they are happy to deal with that as they may.

As has been stated previously, this is not an uncommon problem and I'm glad to have it resolved in this instance.   And, it took a lot of time! 

Dr PR

  • Hero Member
  • *****
  • Posts: 5614
Re: Ah ha!
« Reply #5 on: October 12, 2018, 09:57:28 PM »
Mark,

My "template" idea works like this:

1. I have a 2D drawing that has short lines and curves that either do not connect end to end, or have a huge number of points.

2. I enable the layer(s) containing the short segments or lines with many points, and lock the layer so it cannot be edited.

3. I select an empty layer for the working layer.

4. Then I use Line (V) or Curve (C) to draw new lines on top of the existing lines, using Gravity Snap to set points for the new lines/curves at points on the existing lines on the locked layer. By carefully selecting the points to snap to I create these new lines/curves with the same shape as the originals, but with fewer points and continuous with no gaps.

5. Afterward I can delete the original likes, or just move them to a "Junk" layer in case I want to reference them again.

****

If you save a 3D drawing as a 2D projection ("File/Save As" with the "Save 2-D Projection" option checked) the program will generate a 2D file with bazillions of duplicate line segments and unwanted segments (especially if the 3D drawing has grids in it). These 2D files can be up to 10 times larger than the original 3D files and very slow to work with.

If you import XYZ data sets (such as a topographic map contour lines) any curves will become thousands of short line segments. Again, very large files that are difficult to edit.

The "File/Save As" dialog has two options to help clean up all the unwanted garbage. The "With Hidden Lines Removed" option will clan up some lines that are on top of other line segments, but it misses a lot, and just doesn't work well with grids. The "Enable Hidden Line Cleanup" option actually is too aggressive and will remove some of the necessary line segments.

You can try to delete all the duplicate line segments and extra garbage manually but it can take hours to find the unwanted bits and delete them.

It is MUCH faster to just draw on a new layer, gravity snapping to the points in the original drawing. This also allows you to select necessary points and skip over unnecessary points. And you can combine the line segments or curves any way you want to.

Phil
DesignCAD user since 1987