Corel 'Snap-To' Anomaly (long)

[Lee DeRaud]

Something to watch out for if you require very precise cuts...

Here's a simple example of what's happening:
1. Set 'snap-to-objects' on, 'snap-to-grid' off, and set the display precision to five digits.
2. Draw a rectangle and size it to 4.00000x4.00000, center it at 3.00000,3.00000.
3. Using the polyline tool, draw a line from one corner node to the opposite corner. Repeat for the other pair of corners.

These two lines should be 4.00000x4.00000, centered at 3.00000,3.00000, same as the square, right? No: on my system, they are 4.00234x4.00234, centered at 2.99017,3.00514. Huh?!?

It gets better:
4. Delete the diagonal lines.
5. Rotate the square 45 degrees.
6. Repeat step 3.

The square is now 5.65685x5.65685, still centered at 3.00000,3.00000. That dimension works out to 4.0*sqrt(2), as expected. The diagonal lines (now vertical and horizontal) should be 5.65685x0.00000 and 0.00000x5.65685, still centered at 3.00000,3.00000. Nope:
Vertical: 0.00002x5.65848 at 2.99369,3.00514
Horizontal: 5.65848x0.00002 at 3.00749,2.99134
The change in dimension is at least consistent in X and Y, the change in position is not.

Lest anyone accuse me of being picky, note that these errors are the same order of magnitude as the "kerf width" of the laser. I discovered this anomaly when some cut parts that should have been identical were not. An example:
1. Draw a 4x4 square.
2. Draw a 2x2 square, centered on the 4x4.
3. Draw four lines connecting each corner of the inner square with the adjecent corner of the outer square.
The four lines drawn in step 3 should be identical except for orientation: they're not. Worse, if you cut out the four trapezoids, they don't match.

My first thought was round-off error, but the numbers involved should survive intact using anything more sophisticated than 16-bit integer math. Then I noticed the errors were different depending on which computer I was using. But it's not the computer: it's the screen resolution. The 'snap-to-object' function is apparently using the coordinates of the nearest screen pixel to the node you're snapping to, instead of the actual node coordinates: if you 'zoom-to-selected' on the 4x4 square, the errors are smaller. Of course, if you're working with large objects, that won't help, since as far as I know, you can't pan/zoom after you establish the first node of a multinode drawing operation.

I realize that CorelDraw is not a CAD system, but this is just plain wrong.

[Joe Pelonio]

Lee,

As I first read this I was beginning to think that you have way too much time on your hands, but then I realized it can definitely cause problems for people doing precision work. I just finished cutting a bunch of parts for a
product developemnt company doing a new cell phone prototype. They gave me cad files and it turned out fine, but this means that if I create the file from written specs it could be wrong and/or inconsistent. I may be forced to use my plotter graphics program and export to Corel for some of future jobs. I appreciate your efforts and sharing it. Are you going to forward your testing to Corel Technical Support?

[Lee DeRaud]

As I first read this I was beginning to think that you have way too much time on your hands, but then I realized it can definitely cause problems for people doing precision work. I just finished cutting a bunch of parts for a
product developemnt company doing a new cell phone prototype. They gave me cad files and it turned out fine, but this means that if I create the file from written specs it could be wrong and/or inconsistent. I may be forced to use my plotter graphics program and export to Corel for some of future jobs. I appreciate your efforts and sharing it. Are you going to forward your testing to Corel Technical Support?Well, I do have way too much time on my hands, but that's a good thing.:D

I first ran into this doing those coasters last fall: several of the geometric designs are derived by laying up concentric geometric shapes and adding radial lines between nodes. I thought my laser was having alignment issues, because "identical" parts weren't.:eek:

I'll probably pass this along to Corel, but I'm not sure how much good it will do: I have a feeling (having done a lot of graphics programming in the past) that they'll decide it's more trouble than it's worth..and I'm not sure I can really disagree with that, at least for their core customer base.

What it's probably going to force me to do is use my "big" machine (which is not connected to the laser) for most of my Corel work: it's got a 1280x1024 LCD panel instead of the 1024x768 LCDs that are on the laser machine and my laptop.

[Lee DeRaud]

Here's the response I got from Corel...time will tell whether anything comes of it.

Response (Greg) - 02/15/2006 12:51 PM
Your comments have been forwarded to the appropriate manager here at Corel. Please understand that due to the volume of mail we receive, a personal reply is not always possible. Please rest assured that every message submitted to Corel is read and given proper consideration by management.
As always, feedback and suggestions from our customers are very important and we thank you for your message.
Best Regards,
Greg
Corel Customer Support Services

[Dave Fifield]

Thanks for the heads-up on this Lee. Most appreciated. I will watch out for it and try to compensate where need be. Maybe I can use this as a reason to get LOML to allow me to get that 23" LCD 1900x1200 monitor I've been wanting..... :D

Dave F.

[Rodne Gold]

What version is this? I tried it on 11 and X3 on various puters with various rez monitors and couldnt get it to replicate this?

[Lee DeRaud]

What version is this? I tried it on 11 and X3 on various puters with various rez monitors and couldnt get it to replicate this?Version 12.0.0.458 is what it's showing. I don't know if that number reflects the updates added shortly after installation in early 2005: it still shows a 2003 copyright date.

[Jerry Allen]

Lee,
I tried duplicating what you stated in v12 and X3. The diagonals were correct and everthing located correctly after the rotation. The only thing I noticed was that a straight horiz line which should have been at 5.65685x.00000 was always off at 5.65685x.00002 (and vert as well). I can handle that although it is still off.

v12 should be at ...536. I would recommend a reinstall, update to the latest rev and Pressing F8 when Draw is loading the first time to set the defaults back to factory. Then do your test before altering your settings.


PS--If you add a few more sayings to your byline, subsequent posts will get their own page; a first. :-)

[Lee DeRaud]

Lee,
I tried duplicating what you stated in v12 and X3. The diagonals were correct and everthing located correctly after the rotation. The only thing I noticed was that a straight horiz line which should have been
should been at 5.65685x.00000 was always off at 5.65685x.00002 (and vert as well). I can handle that although it is still off.

v12 should be at ...536. I would recommend a reinstall, update to the latest rev and Pressing F8 when Draw is loading the first time to set the defaults back to factory. Then do your test before altering your settings.Thanks, I'll give it a try...on a machine not connected to the laser.:p

That 0.00002 line-width thing is probably just something the programmer did to keep from getting divide-by-zero exceptions.

[Jerry Allen]

I tried it again at 4 places and it does not appear, as it should not. It does occur at 5 whether redrawn or not deleted and simply rotated.

I don't see what the laser would have to do with it since Corel does not link to the driver like Word does.

[Lee DeRaud]

Jerry, I installed CD SP1 and the version is at ...536 now. The problem remains, but I did discover that it only affects the Polyline tool: everything works as expected with the Freehand tool and the Bezier tool, which may be why you and Rodne didn't see it.

It's still annoying, since what I tend to do is use the Polyline tool to "trace" around regions formed by intersecting geometric shapes. I can do the same thing with the Freehand tool, but I find it less intuitive: Polyline is "click at each node, double-click to end", Freehand is "click to end, double-click to extend" which I find completely bass-ackward.:mad:

[Jerry Allen]

I rarely use the Polyline tool because I am more comfortable with the Freehand tool, although I recognize that being able to use it would be useful. I used the Freehand tool, so I guess that's the reason.
X3 has a new tool, Smart Fill, that automatically creates new objects from intersection of objects or curves. Very cool.

[Lee DeRaud]

X3 has a new tool, Smart Fill, that automatically creates new objects from intersection of objects or curves. Very cool.Ok, that's the first good reason I've seen to cough up the cash for the upgrade.