Intersection of two lines -- Overshoot?

[aclee]

Hi all,

I'm a Solidworks newbie since they only teach/use Pro/E
at my university.

I'm having trouble with lines properly intersecting
and/or mating together.

For example, I would draw a circle, then draw a chord in
the circle (a line from one part of the circle to
another). The when setting the "end" of the line, it
would snap with the edge of the circle and the circle's
line would highlight orange, meaning that the chord is
supposed to be mated already. However, if I zoom in, the
end of the line is not perfectly mated to the edge of the
circle. Instead, it overshoots (see picture), or it would
undershoot (creating a gap).

Sorry if this is hard to understand.

Thanks for any help.
Edited by: aclee

 

[Mihail]

This is not a problem. What you see is not the SW "reality".
The line's end points ARE on the circle. If you drag the line you will see that the end points will follow the circle. So, in SW's mind (SW's math), the points ARE on the circle.
My English is not very good but hope you understand what I mean.

Good luck !

 

[joelewinski]

Mihail is correct. Mathematically, it's 100% correct, graphically not. The closer that you zoom into the circle, you'll notice that it is graphically, a polygon. Therefore, the endpoint APPEARS to be either too short or too long. As long as you see that coincident icon, rest assured that it is mathematically correct.

 

[aclee]

Thank you!

However this sometimes causes
problems for me.

For example this can cause open contour
errors etc.

 

[Mihail]

No. It don't causes errors.
If you have an error something else is wrong not THIS.

Remember: The screen is not like the paper. It is composed of pixels.
The pixel's coordinates are INTEGER numbers.
The real points coordinates are rarely integer numbers, so the routines for display must approximate (and sometimes interpolate) not integer numbers to the integer. This cause the gap you SEE between the circle's points and the end point for the chord.
But the internal relation COINCIDENT is satisfied any time.
If you establish that relation, of course.
Sometimes you SEE a coincident but the RELATION COINCIDENT is NOT there. In THIS case yo will get SURE an error.

Good luck !