tangent to two entities, through a point, when the point belongs to one of the two entities

If you are having problems with QCAD, post here. Please report bugs through our Bug Tracker instead.

Always attach your original DXF or DWG file and mentions your QCAD version and the platform you are on.

Moderator: andrew

Forum rules

Always indicate your operating system and QCAD version.

Attach drawing files and screenshots.

Post one question per topic.

Post Reply
mangel
Newbie Member
Posts: 3
Joined: Sun Sep 12, 2021 2:56 pm

tangent to two entities, through a point, when the point belongs to one of the two entities

Post by mangel » Mon Sep 27, 2021 6:32 pm

When I use the tool: tangent to two entities, through a point, and the point belongs to one of the two entities, Qcad does not solve the problem.

Works well if there are two lines,
but if it is a line and a circle gives false solutions,
and if it is two circles say that there is not solutions.

Tested in Debian Gnu/linux 10 and Qcad 3.26.4.0

User avatar
Husky
Moderator/Drawing Help/Testing
Posts: 4935
Joined: Wed May 11, 2011 9:25 am
Location: USA

Re: tangent to two entities, through a point, when the point belongs to one of the two entities

Post by Husky » Mon Sep 27, 2021 7:08 pm

mangel wrote:
Mon Sep 27, 2021 6:32 pm
When I use the tool: tangent to two entities, through a point, and the point belongs to one of the two entities, Qcad does not solve the problem.
Sorry, never heard about a tool called "Tangent to two entities". I know about a tool called "Tangent two circle (LT2) which works between two circle. Is that the tool what you refer to?
Work smart, not hard: QCad Pro
Win10/64, QcadPro, QcadCam version: Current.
If a thread is considered as "solved" please change the title of the first post to "[solved] Title..."

User avatar
andrew
Site Admin
Posts: 9037
Joined: Fri Mar 30, 2007 6:07 am

Re: tangent to two entities, through a point, when the point belongs to one of the two entities

Post by andrew » Mon Sep 27, 2021 8:19 pm

mangel: please attach your drawing file with the two tangential entities and indicate which exact tool you are using, thanks.

CVH
Premier Member
Posts: 3416
Joined: Wed Sep 27, 2017 4:17 pm

Re: tangent to two entities, through a point, when the point belongs to one of the two entities

Post by CVH » Tue Sep 28, 2021 7:23 am

mangel wrote:
Mon Sep 27, 2021 6:32 pm
When I use the tool: tangent to two entities, through a point, and the point belongs to one of the two entities, Qcad does not solve the problem.
Husky wrote:
Mon Sep 27, 2021 7:08 pm
Sorry, never heard about a tool called "Tangent to two entities".
Draw circle tangential to two entities, through a point (CT2).
Andrew, all my findings are in the attached dxf files ... Not limiting. :wink:

- With 2 lines and a point on one of the lines QCAD presents 2 correct solutions.
The indicated point is then the (forced) tangent point with that line.
Solutions reduce to one unique if the lines are parallel.

- With a circle, a line and a point on the line QCAD may present 4 solutions of which none is correct.
If the indicated point is exactly the center projected perpendicular on the line, a lucky shot or by an auxiliary line, ...
... then 2 correct solutions are presented.
With 4 solutions it is clearly visible that the indicated point is an intersection with the line and that all the solutions intersect twice.
CT2-Line-Circle-Point.dxf
(103.38 KiB) Downloaded 344 times
For the correct solutions:
The tangent point of two circles is on a line through both centers. (Cyan)
And the center of a circle tangent to a line is on a line orthogonal in the tangent point. (Blue)
One can find these correct solutions by the intersection of 2 incorrect solutions. :P :wink:

- Analog with a line, a circle and a point on the circle.

- With two circles there will not be a solution for a point inside one of the circles.
The solution can't be and tangent to and crossing the circle at the same time.
For a point outside the circles 4 solutions may be presented. Not all 4 are correct in all cases.
CT2-Circle-Circle-Point-1.dxf
(101.41 KiB) Downloaded 334 times
For a point on one of the circles there are no solutions presented.
These can be found by mirroring the other circle over the symmetry axis center - point and matching solutions of 3 tangents (CT3). :P :wink:
CT2-Circle-Circle-Point-2.dxf
(101.88 KiB) Downloaded 344 times

This knowledge is gathered in the past few months while I investigated how to round all corners of bulging polylines.
It boils down to what is considered tangent, what is the intersection of two circles, and how arc segments are prepended/appended to a polyline.
The tool is perfectly functional up to a point where the numbers don't add up anymore. They should mathematically.

Regards,
CVH


Post Reply

Return to “QCAD Troubleshooting and Problems”