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Perpendicular Snap Not Working

Posted: Thu Nov 08, 2018 11:53 pm
by asdfqwert
I'm getting some really bizarre results with perpendicular snap. Some of the time it works fine, but with certain lines it chooses an arbitrary and random angle as "perpendicular". See the picture:
Screen Shot 2018-11-08 at 2.37.37 PM.png
Screen Shot 2018-11-08 at 2.37.37 PM.png (38.91 KiB) Viewed 1054 times
Lines A and B were already drawn, I dragged the ends to the "perpendicular" snap points along D and this is what I got. I made the line C as a test, and it oriented correctly. I tried to make both A and B perpendicular to C, and it didn't give me a snap point anywhere along C for either line. I moved the end of C off of D, then couldn't find the perpendicular snap point again.

I have auto snap on, with perpendicular snap enabled in application preferences. I'm running Qcad Pro version 3.21.3 on OS X 10.13.6. This is one of several DWG files that I got from an architect running Archicad. I'm having this trouble on at least one of the other files.

Is there some setting I'm not aware of, or is this just a bug?

Re: Perpendicular Snap Not Working

Posted: Fri Nov 09, 2018 12:05 am
by andrew
Perpendicular means "perpendicular to the (often imaginary) line between the current position of the relative zero point (small red circle with cross) and the entity closest to the mouse cursor".

When drawing lines, perpendicular means "perpendicular to the line that is being drawn" since the relative zero point is automatically moved to the start point of the line when it is drawn.

However, when dragging an endpoint of a line, the relative zero point is moved to the original position of the point that is being dragged. The perpendicular line is then not the line you happen to be dragging but the imaginary line between the relative zero point and the entity. In other words, your movement of the dragging is perpendicular to the entity.

Before you say "but this should be different": Notice that you could be dragging multiple endpoints of multiple lines or even other entities such as arcs or splines, etc. Perpendicular might then be ambiguous.

When dragging the endpoint of a line you could move the relative zero point manually to the other endpoint of the same line (Snap > Set Relative Zero) to achieve what you intended.

Re: Perpendicular Snap Not Working

Posted: Fri Nov 09, 2018 12:21 am
by asdfqwert
andrew wrote:
Fri Nov 09, 2018 12:05 am
Perpendicular means "perpendicular to the (often imaginary) line between the current position of the relative zero point (small red circle with cross) and the entity closest to the mouse cursor".

When drawing lines, perpendicular means "perpendicular to the line that is being drawn" since the relative zero point is automatically moved to the start point of the line when it is drawn.

However, when dragging an endpoint of a line, the relative zero point is moved to the original position of the point that is being dragged. The perpendicular line is then not the line you happen to be dragging but the imaginary line between the relative zero point and the entity. In other words, your movement of the dragging is perpendicular to the entity.

Before you say "but this should be different": Notice that you could be dragging multiple endpoints of multiple lines or even other entities such as arcs or splines, etc. Perpendicular might then be ambiguous.

When dragging the endpoint of a line you could move the relative zero point manually to the other endpoint of the same line (Snap > Set Relative Zero) to achieve what you intended.
Thanks for the explanation. That makes a lot of sense in terms of the behavior I've been experiencing, but it seems like much less useful behavior than what I'm trying to do. How would I go about setting the relative zero point while also moving the other end of the line? As soon as I select the end to move, the zero point moves, and I can't see any way to set it while I have that end selected.

Re: Perpendicular Snap Not Working

Posted: Fri Nov 09, 2018 6:39 am
by Husky
Hi,

I've to confess that I never understood how this works and I'm always working around the problem. Maybe I can learn it now too ... :shock:
andrew wrote:
Fri Nov 09, 2018 12:05 am
When dragging the endpoint of a line you could move the relative zero point manually to the other endpoint of the same line (Snap > Set Relative Zero) to achieve what you intended.
asdfqwert wrote:
Fri Nov 09, 2018 12:21 am
As soon as I select the end to move, the zero point moves, and I can't see any way to set it while I have that end selected.
I took screenshots which explains the same struggling and unfortunately I can't solve it with Andrews explanation too.

Example:
I draw lines in a 1, 2, 3 order. Three was direct placed perpendicular on 1. No problem!

Husky-2018.11.08-07.png
Husky-2018.11.08-07.png (19.09 KiB) Viewed 1031 times

Then - following your description - I placed RZ as marked on line 2 and tried to drag the other end perpendicular on line 1. It shows a perpendicular info on the mouse pointer but it isn't correct. That is perpendicular to the other end of the line (not to RZ!) where I snapped the line to drag it to 1. Looks like RZ is ignored / moved? I tried also to lock RZ without any luck.


Husky-2018.11.08-01.png
Husky-2018.11.08-01.png (33.48 KiB) Viewed 1031 times
Husky-2018.11.08-03.png
Husky-2018.11.08-03.png (29.86 KiB) Viewed 1031 times

Haven't I understood the solution correctly or is there a trick?

Current QCAD Version / Win10

Re: Perpendicular Snap Not Working

Posted: Fri Nov 09, 2018 10:16 am
by andrew
I hope this helps (step by step):
1. Select entity or entities you want to change by dragging a reference point:
Screen Shot 2018-11-09 at 09.02.19.png
Screen Shot 2018-11-09 at 09.02.19.png (35.12 KiB) Viewed 1022 times
2. Move the mouse cursor on top of the reference point you want to drag:
Screen Shot 2018-11-09 at 09.02.19 copy.png
Screen Shot 2018-11-09 at 09.02.19 copy.png (37.9 KiB) Viewed 1022 times
3. Press the left mouse button and hold it down (don't let go).
4. Move the mouse a significant distance away from its current location, thereby starting to drag.
5. As soon as you can see a preview of the dragging operation, let go of the left mouse button.
6. If you drag to the target line now, the perpendicularity is between the original position of the reference point (= position of the relative zero point) and the target line. I.e. the green line is perpendicular to the white target line:
Screen Shot 2018-11-09 at 09.06.15.png
Screen Shot 2018-11-09 at 09.06.15.png (65.29 KiB) Viewed 1022 times
7. Since we want a different perpendicularity, we have to move the relative zero point. Choose Snap > Set Relative Zero (or type RZ if you want to be quick) and click the startpoint of the line you want to be perpendicular to the target line:
Screen Shot 2018-11-09 at 09.09.23.png
Screen Shot 2018-11-09 at 09.09.23.png (42.74 KiB) Viewed 1022 times
8. Approach the target line and find the new perpendicular point and click it:
Screen Shot 2018-11-09 at 09.11.36.png
Screen Shot 2018-11-09 at 09.11.36.png (56.14 KiB) Viewed 1022 times
Note: in QCAD you can start almost any tool at almost any time without terminating the current tool. If you are adventurous, try to start drawing a line by setting its start point, then draw a circle, right-click and set the end point of the line tangential to that circle. You can even start a line, then start the line tool again, draw another line, right-click twice and finish the first line. This is handy if you start something and then realize you need an auxiliary construction to finish it. Just go ahead and create the auxiliary construction, then finish what you were doing.

Re: Perpendicular Snap Not Working

Posted: Fri Nov 09, 2018 8:14 pm
by Husky
andrew wrote:
Fri Nov 09, 2018 10:16 am
Note: in QCAD you can start almost any tool at almost any time without terminating the current tool.
Ahhhhhhhhhhhhh - that is the trick. :lol:

Thanks for the explanation - works like a charm!

Re: Perpendicular Snap Not Working

Posted: Fri Nov 09, 2018 11:06 pm
by asdfqwert
Yes very helpful, thank you!