Author Topic: 2D arrows  (Read 1485 times)

Dr PR

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2D arrows
« on: November 08, 2013, 12:02:53 PM »
I would like to see arrows that behave like 2D text - with the line and arrowhead plane always perpendicular to the line of sight.

In the "original arrows" drawing I created an arrow and then made a circular array of eight. Above this I placed the 2D text "ORIGINAL ARROWS." Notice  how all arrowheads are clearly visible.

Then I rotated the view and made the "rotated view" image. I changed the 2D text to read "ROTATED VIEW." Notice how some of the arrowheads almost disappear? This isn't good, especially if you have added comments to a 3D drawing and you need to create images from many different view angles.

It would be nice to have "2D arrows" that behave like the 2D text, always facing the viewpoint.

Phil
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magic

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Re: 2D arrows
« Reply #1 on: November 08, 2013, 02:36:54 PM »
Hi Phil,

You mean like Rotate View vs. Rotate as seen in this video clip: http://www.magicsystems.com/Arrowhead%20-%20Rotate%20View%20vs%20Rotate.htm?
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Lar

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Re: 2D arrows
« Reply #2 on: November 08, 2013, 06:14:54 PM »
Phil,

Since I do construction drawings in 3d I run into this issue often when notating. This normally happens with 2 point arrows.

A trick I have learned is that, while viewing from the angle you need, if you put a 3rd point in the middle and move it out so the arrow has a bend in it then the arrowhead will turn to face the viewer.

If it's important that the arrow appear to be straight then move the middle point ever so slightly out of line. The arrowhead will face the viewer while the arrow appears to be straight.

Lar
ps: I guess I should add this to the tricks and tips dept...
« Last Edit: November 08, 2013, 06:25:21 PM by Lar »

Dr PR

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Re: 2D arrows
« Reply #3 on: November 08, 2013, 09:58:35 PM »
magic,

Rotate view with "Set View by Drawing Center" causes the arrowhead to just about disappear when the view is rotated 90 degrees.

Lar,

I tried what you said and it has no effect on the problem I described. The arrowhead stays in the plane it was originally created in even if the arrow shaft has an extra point (added in Point Select mode) that makes it a bit curved. Adding the point may cause the arrowhead to rotate into a new plane, but when the view is rotated the arrowhead disappears as described above. In other words, the arrowhead does not stay in the view plane (perpendicular to the line of sight).

Worse still, if you have a bunch of arrows that were created in different view rotations they do not all look alike.

I am looking for an arrowhead that is not in a fixed plane, but rotates with the plane of view the way 2D text does. All we have now are "3D" arrows that behave like 3D text.

Phil
« Last Edit: November 08, 2013, 10:02:39 PM by Dr PR »
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magic

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Re: 2D arrows
« Reply #4 on: November 08, 2013, 10:09:41 PM »
Hi Phil,

I second your motion!
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Dr PR

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Re: 2D arrows
« Reply #5 on: November 08, 2013, 10:26:01 PM »
Here is an even stranger arrow behavior.

Open a new 3D drawing.

Rotate the view 90 degrees around the Y axis.

Draw an arrow - you can't see the arrowhead!

Rotate the view back to 0 degrees and you can see the arrowhead again.

Phil
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Rob S

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Re: 2D arrows
« Reply #6 on: November 09, 2013, 08:28:59 AM »

Putting together a couple of earlier posts, I think the solution would best be implemented as a true 3-D cone-shaped arrowhead!

Now to keep it oriented correctly on a 3-D spiral curved line!!!

I think the solution where it works like 2D text might not have the desired effect, as the arrow would end up not pointing where it should.  Else how would you handle the arrowhead as you begin to view the arrow along its length??
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Dr PR

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Re: 2D arrows
« Reply #7 on: November 09, 2013, 09:13:31 AM »
Rob,

Good question. Not only does the arrowhead need to rotate with the view, but the line must do so also. If the arrow shaft is a wide line it is essentially a visual 2D plane. This plane must be kept coplanar with the arrowhead plane.

The problem with cone arrowheads is that they shade as cones and they cast shadows. The line shaft of the arrow does not cast a shadow. Shadows would be a very bad thing in a shaded 3D drawing.

Cones do not shade evenly because they are curved surfaces, and this shading effect makes eack "arrowhead" look different from all others at different angles to the light. It really looks pretty crummy!

You can make the cones the "Black" material and use Phong rendering to get them to come out black black - and they will show little effect of the rendering. But you can't use black arrows over black surfaces, so you will need some other colors. All other colors will produce pretty ugly cone arrowheads.

I don't see what the problem is here. 2D text is far more complex than a simple arrow. If they can get the text to rotate properly surely it can be done with arrows.

Phil
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Rob S

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Re: 2D arrows
« Reply #8 on: November 09, 2013, 08:44:34 PM »
I don't think it is so easy.  Text is fixed at its insertion point, and you don't care where in space the other end goes, it is simply drawn extending out from that insertion point perpendicular to your line of sight.

Let's say an arrow extends from a starting point at line of text to a point on the drawing.  I would expect both ends to remain where they are.

If it were like 2D text, as you rotate the view, unless the rotation is about the axis of the arrow, in order to remain perpendicular to your line of sight, either the point of the arrow would move away from the destination point, or its starting point would have to move away from the text.

If not, then if you rotated the view 90 degrees from the current direction of the arrow, you might end up seeing a point in space with an arrowhead attached.

I will attempt to demonstrate this tomorrow, by drawing an arrow consisting of the characters --------> drawn as 2D text, and see what happens.


Primitive example now attached below, open it and use "Set view by view centre" to see the effect of rotating these.
« Last Edit: November 10, 2013, 02:44:59 PM by Rob S »
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samdavo

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Re: 2D arrows
« Reply #9 on: November 09, 2013, 09:49:39 PM »
Some people use small circles (spheres?)  for arrowheads.  Would that help?