Topic: Find opposite points diagonally

[Coder]

hello guys .

I am stick with one problem and I hope someone can help me with it . 

I have the points p1 and p2 and I need to find p3 and p4 .

is it difficult  ?

Code: [Select]

(if (and (setq p1 (getpoint "\n first point :"))
         (setq p2 (getpoint p1 "\n second point :"))
         )
  (progn
  ( ................


Many thanks .

[David Bethel]

You're going to need more information than just 2 points.  Any other know values or predetermined conditions ?  -David

[Coder]

You're going to need more information than just 2 points.  Any other know values or predetermined conditions ?  -David

Thank you David .

I am sorry not  , I am after to draw a box with the four points and offset box from the first one .

[ronjonp]

Look into vlax-curve-getclosestpointto.
(vlax-curve-getclosestpointto (car (entsel)) (getpoint))

[Bhull1985]

The two bounding lines would be good info for finding angle, rise/run

[Coder]

Look into vlax-curve-getclosestpointto.
(vlax-curve-getclosestpointto (car (entsel)) (getpoint))

I don't have line to select , I need to get the points 3 and 4 after specifying the points 1 and 2

The two bounding lines would be good info for finding angle, rise/run

I did not understand your reply Bhull 

[CAB]

In addition to p1 and p2 you will need one angle.

[efernal]

if you have a line p1/p3 or p2/p4 so you have the angle...

[irneb]

From the screen cap it seems you already have the 2 bounding lines. After picking P1 & P2 it should then be possible to select those lines from those points (no further user input needed) - you could use ssget for this (send the P1 & P2 points as single selection points to ssget). From this you then have the angle(s) to calculate P3 & P4. If you don't want to calculate then what about using osnap to pick the perpendicular points as-and-when you pick 1 & 2 (you might have to fiddle with the lastpoint setvar to work out the correct perp)? If the lines are always longer than the resulting "rectangle" then you could also simply use the vlax-curve-getClosestPointTo.

E.g. here's the quickest way I know of doing this without ssget and only using old ALisp functions:

Code - Auto/Visual Lisp: [Select]

1. (if (and (setq p1 (getpoint "\n first point :"))
2.          (setq p2 (getpoint p1 "\n second point :"))
3.          )
4.   (progn
5.     (setq p3 (osnap p1 "_Perp"))
6.     (setvar "LastPoint" p1)
7.     (setq p4 (osnap p2 "_Perp"))
8.     ;; Continue using the 4 points here
9.   )
10. )

If your screen cap is indicating something other than 2 bounding entities, then there's no way for ACad to "know" what angle the rectangle is to be drawn at. You need to specify it somehow, either ask the user to provide the angle, or default to the current UCS.

[CAB]

See reply #5, he said he doesn't have a line to select.

[Coder]

See reply #5, he said he doesn't have a line to select.

That is correct ,

The grey colored hidden lines representing a wall and the other two lines are the two sides of pipe , and I want to find the other two points p3 and p4 .

Many thanks

[snownut2]

Would you know the distance say p1 to p4 or p1 to p3, that would work. (angle would not matter)

Then you could do a distance/distance intersection type of function to create points p3 & p4.

[Bhull1985]

"bounding lines" are the lines that pass through points p1 and p3, and p2 and p4 respectively.
The line that is created by going through either set of these two points in relation to the p1-p2 line, doing an angle command on those two lines will tell you your base angle.
your base angle minus 90 degrees will tell you the angle at which to draw your new line from p2 to leave a perfect 90 perpendicular system as shown in the screencap...I think

[snownut2]

The included angle from p1 to p2 to p4 is definitely not 90deg.  That is the problem in trying to get you an answer....

[CAB]

See reply #5, he said he doesn't have a line to select.

That is correct ,

The grey colored hidden lines representing a wall and the other two lines are the two sides of pipe , and I want to find the other two points p3 and p4 .

Many thanks

If the pipe and / or wall exist (no lines but pline or block object) then that would work for establishing a perpendicular.