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3 Points, 3 Lines

jcsteele560
Participant

3 Points, 3 Lines

jcsteele560
Participant
Participant

Hi everyone,

 

I have three points in AutoCAD which need to be at a specific spacing apart.  I also have three lines which need to be at a specific angle apart.

Is there any way in which I can have the lines lying on the points without upsetting the point position or angles between the lines? Maybe using the parametric constraints in some way perhaps?

I have attached a JPEG along with this post.

 

Best regards,

 

Chris

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Alfred.NESWADBA
Consultant
Consultant

Hi,

 

>> Is there any way in which I can have the lines lying on the points without

>> upsetting the point position or angles between the lines?

If line-angles are fixed and the point-positions are fixed then just use command _MOVE, select each line and move the line from (objectsnap) endpoint of the line to (objectsnap) node to the point.

 

20171118_113918.png

 

If you expect all 3 lines to meet in one intersection point ... then no, I don't see a (mathematical) solution for that.

 

- alfred -

------------------------------------------------------------------------------------
Alfred NESWADBA
ISH-Solutions GmbH / Ingenieur Studio HOLLAUS
www.ish-solutions.at ... blog.ish-solutions.at ... LinkedIn ... CDay 2025
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(not an Autodesk consultant)
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leeminardi
Mentor
Mentor

Let's label the lines 1, 2, and 3,  and the points as A, B, and C.

Resection-LABELED.jpg

 

If I understand your goal, you would like to keep the points where they are and reposition the lines, without changing their orientation, so that the pass through their respective points and STILL INTERSECT AT A POINT.  YES?

 

Requiring line 1 to pass through A and line 2 to pass through B you have fixed the intersection point where they meet. You cannot create a line through an arbitrary point C with a specified angle and have it pass through the intersection point established by 1 and 2.  Is there a constraint here that can be eliminated?  Does line 3 have to pass through the same intersection point of 1, 2?

 

 

lee.minardi
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jcsteele560
Participant
Participant

Hello Iminardigmail,

 

Yes, that's exactly what I'm looking for - Line 1 to lie on Point A, Line 2 to lie on Point B and Line 3 to lie on Point C but maintain the angles between Lines 1,2 and 3.

 

This is part of a surveying exercise where I'm to find out the co-ordinates of the intersection point the three lines create (call it D) but I'm trying to accurately find out where Point D is.

 

Many thanks and kind regards for the replies,

 

Chris

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leeminardi
Mentor
Mentor

What does the surveying exercise say about handling error?  Since the three lines do not intersect exactly at a point then some method must be used to address the error.  One approach may be to make a line parallel to 3 passing through point C and then extend each line until it intersects with both of the other lines.  You can then construct a circle through the 3 intersection points (red circle) or draw a circle tangent to the three lines (yellow circle), or use some other rule.  This construction is very easy in AutoCAD.

 

On a related note, I recommend an excellent book on the origins of handling surveying error (regression analysis).  It is "The Measure of All Things" by Ken Adler.  It is the story of how the length of the meter was first established and in the process the importance of handling error in measurements. 

 

Resection-LABELED2.jpg

 

 

lee.minardi
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jcsteele560
Participant
Participant

Hi Iminardigmail,

 

As far as I know in geometry, there can be only one specific point that Point D can lie due to the constraints of lines on points.  I have attached a screenshot as close to my goal as possible but it is not completely accurate.

If I move one line, another line will move off the point.  I was hoping AutoCAD could control this in some way with parametric modelling.

 

Best regards,

Chris

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leeminardi
Mentor
Mentor

Chris, I don't think we are understanding each other. Given 3 points with lines going through them at a given angle, it is unlikely that the 3 lines will intersect at a point.  Let's say the angle of your line 3 going through C were slightly different.  Line 3 would no longer pass through D but lines 1 and 2 would.   You couldn't make line 3 pass through D (which cannot change due to it being defined by lines 1 and 2) without changing its angle or moving point C. It is not a question of AutoCAD finding a solution but your problem statement, as I understand it, makes it an impossible task.  

lee.minardi
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parkr4st
Advisor
Advisor

There is nothing that prohibits rotating the three lines as a block?

 

if not then as long a line 1 stays on point a and line 2 stays on point b there is a solution of rotate and moving that will put line 3 on point 3 and the Relative angle between the lines stays the same.

 

 

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jcsteele560
Participant
Participant

Hi parkr4st,

 

Yes, you're correct.  There is nothing prohibiting the lines from rotating on each point - the only rule is that the points don't move and the angle between the lines don't move.

 

Imagine the situation where the lines are 3 x steel beams welded together and the three beams are to sit on three columns.  The intersection of the three beams must sit somewhere in space.  My goal is to find out that position.

 

In the context of some other CAD programs, the lines are constrained to linear movement on the point but there is also rotational movement too.

 

Many thanks and best regards,

Chris

 

 

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leeminardi
Mentor
Mentor

So the lines as a group can rotate!!!  I thought this was a surveying problem where the bearing (angle) was fixed.

 

The solution is quite easy with AutoCAD's parametric constraints.

s1.JPG

  1. Place a Fix constraint on the 3 points
  2. Place angle dimensions between two sets of the lines.  Note, in the image below I added a reference dimension (29°) to show the rotation angle after all constraints have been applied.
    s2.JPG


  3. Place coincident constraints
    1. between the end of line 1 and line 2 (where they intersect)
    2. between the end of line 1 and line 3
    3. between the free end of line 1 and point 1
    4. between the free end of line 2 and point 2
      s3.JPG
  4. And finally between the free end of line 3 and point 3

s4.JPG

 

Note, the three lines have been rotated approximately 4°.  Quick properties will show many decimal places.

 

 

lee.minardi