Line intersections not recognized

[Dstephenson]

Why does AutoCAD 2008 tell me that there is no intersection between two lines that clearly cross each other? Note that both lines have zero Z coordinates, zero angles in the z plane, are flattened, and clearly cross each. What’s more frustrating is that I can trim either line using the other as a cutting edge, but still, AutoCAD tells me that they do not intersect! Any advice would be greatly appreciated.

[NBC]

could you post a sample of your drawing ?

[CADguy209]

Make sure your UCS is set to world and double check the lines. If youre origin is not at world and one of the lines was draw while in this other ucs position it will list the z as being 0.

Also depending on your units and how the percision is set its possible for one of the lines to be in a different z but becuase its bellow what your percision is set to it will display it as being at 0 when you do a list on it. When in doubt rotate about your x axis 90 and do a plan view to the current ucs.

[Shiloh]

Sounds like the classic "your lines are not on the same plane" problem. We get that all the time with files that are sent to us from civilcad or some other program in 3d and simply flattened.

[Hedgehog]

Sounds like the classic "your lines are not on the same plane" problem. We get that all the time with files that are sent to us from civilcad or some other program in 3d and simply flattened.

Except that it's already been stated that they are at z=0 & angle in z=0.

This is an interesting one & it'd be good if you posted a block of the offending lines to have a look... remember that things can get a bit unpredictable at extreme scales or distances from wcs 0,0,0... though I must admit CADguy's precision suggestion sounds most likely.

[BOB'27T]

Along with what Shiloh said, the lines may have an elevation difference. I have this happen when I try to join or fillet, if the lines each have a different elevation.

[CADken]

this may be a total shot in the dark, but when is the last time you updated your drivers? sounds like it may be a graphic driver or something....

[Teeds]

this may be a total shot in the dark, but when is the last time you updated your drivers? sounds like it may be a graphic driver or something....

This may be part of the issue, but not all of it.

I have had it happen when one of the lines is a dashed line and they happen to cross in the broken area.

Sometimes ACAD doesn't seem to recognize a line regardless of the fact that I can see it. The only solution for me in that case is to save the drawing, exit it and reload it and then ACAD sees the line. I chalk it up to the software gods not liking my vibes at that moment.