tangent to spline or any curve

[cad manty]

Dear Friends,

hi i m new here and a new user of AUTO CAD 2010.

Can anyone tell me how to draw a tangent to any curve(basically a spline).

[MSasu]

Check the Tangent OSNAP mode (i.e. + right-click when asked for points).

 

Regards,

Mircea

[cad manty]

kindly elaborate............i m not able to understand

[cad manty]

dear msasu.........please explain this step by step..........thanks a lot

[MSasu]

Please follow the steps below:

• Call LINE command.
  
• Pick an arbitrary point.
  
• Press & right-click on the mouse and select Tangent from the menu that pop-up.
  
• Select the curve close to where you want to have the tangent drawn.
  
• End the line command.
  

This will help you understand the way this OSNAP mode works.

 

Regards,

Mircea

[cad manty]

Dear msasu.......thanks for the reply .............this has really helped me a lot.............but the problem is that i wanty to draw tangent on the curve at selected/desired point.......the method explained by you picks up the point of tangency automatically.

So kindly explain how to draw tangent on any curve at a point defined by user on the curve.

[MSasu]

For an arc/circle is easy – it is the perpendicular on the radius drawn on that given point; for a spline, the only way I see is to do it programmatically (i.e. AutoLISP).

 

Or, if you know the distance from first point of spline to that particular point (measured along curve) can use the MEASURE command with a block and Aligned option to get the perpendicular on curve at that point – the tangent is the perpendicular on that.

 

Regards,

Mircea

[eldon]

One way is to offset the curve, and then draw from the given point a line which is perpendicular to the offset line. Now the tangent is at right angles to the line you have just drawn.

[MSasu]

Interesting solution, thanks for sharing it. Only one comment: this is an approximation and the precision is inverse proportional with offset distance.

 

Regards,

Mircea

[SEANT]

Also –

 

 

 

The XLINE command has some advantages for this type of osnap query. A command sequence:

 

 

 

Command: _xline Specify a point or[Hor/Ver/Ang/Bisect/Offset]: tan

 

to

 

Specify through point: nod

 

of

 

Specify through point:

 

 

 

 

 

 

This sequence will work well for convex entities (circle,ellipse, splines, etc). Problems do arise, however, if a spline wraps back on itself. In that instance it may be more sensible to use PER, and rotate 90 to get back to tangent (as similarly suggested by eldon).

 

 

 

Command: _xline Specify a point or[Hor/Ver/Ang/Bisect/Offset]: per

 

to

 

Specify through point: nod

 

of

 

Specify through point:

 

 

 

Command: ROTATE

 

 

 

Current positive angle in UCS: ANGDIR=counterclockwise ANGBASE=0

 

 

 

Select objects: last

 

1 found

 

 

 

Select objects:

 

 

 

Specify base point: nod

 

of

 

Specify rotation angle or [Copy/Reference] : 90

Edit: The TAN method is so tempormental that it is probably better to just use the PER variant.

[Tyke]

Interesting solution, thanks for sharing it. Only one comment: this is an approximation and the precision is inverse proportional with offset distance.

 

I just tried eldon's suggestion on a spline, using a 2m offset and a 200m offset. I lengthened the 2m line to 200m and measured the distance between the end points of the two lines, it was 11mm. I reckon for most practical purposes the difference is negligible.

[MSasu]

My testing method was to draw a tangent to spline from an arbitary point and after use @eldon’s solution from the end of that line and measured the angle.

You are right, the deviation is very small (2nd or 3rd decimal).

 

Regards,

Mircea

[cad manty]

dear eldon ...........

how can offset of a curve can be line

[cad manty]

thanks a lot everybody for your comments and suggestions.................Mr. eldon ....your idea of offset is fabulous............i have cross checked on a similar spline in autocad and than compared the results on solidworks drawing modules ...........the results match on dot values...........great.

Thanks.

 

 

regards

Manty