Snap to Center of Arc

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RobertMcManus
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Snap to Center of Arc

Post by RobertMcManus » Sat May 16, 2020 9:22 pm

This seems very basic but it just won't work for me. I'm trying to snap to the center of an arc, say for the start point of a line. If I type sc or select the center snap the cursor will snap to the center of circles and some arcs, not not all arcs. If I first select the arc and see the magenta center reference the cursor will still not snap to that reference point. If I hover near objects it will find the center of circles and some arc but not all arcs.
QCAD Circle snap.JPG
Can't snap to the center of this arc
QCAD Circle snap.JPG (46.94 KiB) Viewed 442 times
. Thank you.

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andrew
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Re: Snap to Center of Arc

Post by andrew » Sat May 16, 2020 9:29 pm

Just to make sure we're on the same page: Note the difference between "middle of arc" (middle of the arc's length, along the arc line) and "center of arc" (center point at the center of the circle out of which the arc is a part).
Screenshot 2020-05-16 at 22.25.02.png
Screenshot 2020-05-16 at 22.25.02.png (104.25 KiB) Viewed 438 times
If you cannot snap to the center of an arc using snap to center, please attach the drawing and indicate which arc.

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RobertMcManus
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Re: Snap to Center of Arc

Post by RobertMcManus » Sun May 17, 2020 4:49 pm

Thank you for the response. Yes, I sometimes confuse the middle and the center snap, but I usually type SC without using the sidebar. I have modified the file since posting, but can recreate the issue here. With the arc selected as shown, I can snap to the center by hovering near the arc itself, but not near the magenta center reference. However, I can snap to the center of the three concentric arcs to the left by hovering near the arcs OR the arc center itself. Is there a reason the magenta highlighted center will not snap? File is attached. I'm using QCAP Pro on Windows 7.
QCAD Circle snap 2.JPG
Can't snap to the selected arc center.
QCAD Circle snap 2.JPG (89.06 KiB) Viewed 405 times
Attachments
QCAD Pro Arc Snap Example.dwg
Example file for arc snap.
(21.63 KiB) Downloaded 39 times

CVH
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Location: Belgium; Antwerp

Re: Snap to Center of Arc

Post by CVH » Sun May 17, 2020 5:14 pm

This has a lot to do with being nearer to then ....

But in this case there is a spook at the sow said center.
A null-line at -940.61954133, -514.51835950
And the middle of that is chosen.

One can see this by the Arc/Circle that is grayed a bit while a center is previewed.
You can even see Qcad guessing while moving a bit.
Even cleaned up the left centers are more widely found.
But you can't get those centers comming form the opposite side...

Regards,
CVH
QCADpro 3.25.2.1 / win7pro 32 bit / 4GB / 1e generation i7 2.6Ghz / HDD GeForce GT 520

RobertMcManus
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Joined: Sat May 16, 2020 8:58 pm

Re: Snap to Center of Arc

Post by RobertMcManus » Mon May 18, 2020 7:37 am

Thanks for your help. I was able to find the "null Line" (a line with length of zero) using rectangle selection and delete it.

Alas, I find that that there are still some arcs for which it impossible to select the center, such as the dashed blue arcs in the lower left. I can see now that if "snap center" is on the snapping algorithm does not select the center of the entity closest to the cursor, it selects the entity close to the cursor whose center is calculated to be closest. I find this to be unlike other CAD software I have used. It makes it impossible to select the center of an arc with large radius of there is a line close by because the middle of the line is always closer than the center of the arc. Please let me know if I have stated this incorrectly.

Suggestion 1: SC should snap only to circles or arcs, not to lines. SM is already available to snap to the middle of lines.
Suggestion 2: SC should snap to the actual centers of entities as well as the entity itself.

Both of these suggested behaviors are common to other CAD I have used. Other than that, I find QCAD to be very powerful and useful.

One more quick question: It is possible to change the "highlight color" of the entity that is snapped to? I did not even notice the entity was "grayed" until you mentioned it above because my line weights are very thin. Did not see this option in the application preferences.

Thank you again.

CVH
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Joined: Wed Sep 27, 2017 4:17 pm
Location: Belgium; Antwerp

Re: Snap to Center of Arc

Post by CVH » Mon May 18, 2020 8:02 am

RobertMcManus wrote:
Mon May 18, 2020 7:37 am
I can see now that if "snap center" is on the snapping algorithm does not select the center of the entity closest to the cursor, it selects the entity close to the cursor whose center is calculated to be closest.
That is a part of the story but it doesn't hold always.
RobertMcManus wrote:
Mon May 18, 2020 7:37 am
One more quick question: It is possible to change the "highlight color" of the entity that is snapped to? I did not even notice the entity was "grayed" until you mentioned it above because my line weights are very thin. Did not see this option in the application preferences.
Thats another topic.
But yes: Application Preferences (ctrl+,) ... Graphics View ... Colors

Regards,
CVH
QCADpro 3.25.2.1 / win7pro 32 bit / 4GB / 1e generation i7 2.6Ghz / HDD GeForce GT 520

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