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# How do you make a perfect circle?

Discussion in 'Bob's Track Builder' started by nfshp253, May 3, 2009.

1. ### nfshp253

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How to make a perfect circle of radius 2km? Can't seem to get a perfect circle if I use the "Create closed loop track" and use 8 points on the track. Trying to make the Nardo Test Track.

2. ### zaxxon

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You can use only 4 nodes and Entry and Exit Distances of 1103.568 m
(http://www.tinaja.com/glib/ellipse4.pdf)

You can create a project with BTB 0.6, create a closed track with 4 nodes (doesn't matter what coordinates) and substitute those nodes for this ones

<node NodeId="0">
<Position x="0" y="0" z="2000" />
<ControlPoints AngleXZ="-1.570796325" AngleY="0" EntryDistance="1103.568" ExitDistance="1103.568" />
</node>
<node NodeId="1">
<Position x="2000" y="0" z="0" />
<ControlPoints AngleXZ="0" AngleY="0" EntryDistance="1103.568" ExitDistance="1103.568" />
</node>
<node NodeId="2">
<Position x="0" y="0" z="-2000" />
<ControlPoints AngleXZ="1.570796325" AngleY="0" EntryDistance="1103.568" ExitDistance="1103.568" />
</node>
<node NodeId="3" Selected="True">
<Position x="-2000" y="0" z="0" />
<ControlPoints AngleXZ="3.14159265" AngleY="0" EntryDistance="1103.568" ExitDistance="1103.568" />
</node>

If you are really interested on using 8 nodes you can use Entry and Exit distances of 530.4062 m (instead of 1103.568)
In that case the AngleXZ values should follow pi/4 steps.
I haven't tested this 8-nodes case, but it should work.

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3. ### nfshp253

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What do you mean by Entry and Exit Distances? I don't understand and don't know where to adjust. Anyway, I tried the same coordinates for the four points but it turned out to become this weird shape! Anyway I'm a total NOOB at this program, I don't even know how to change the camber for different points of the track

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4. ### zaxxon

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292
Ratings:
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Each node has two control points, one for the entry and one for the exit
(see image attached). I see this control points in a pink color. You move the control points to give shape to the circle.

You must use a separation of 1103.568 m between the node and the control points (in the tangential direction, of course).

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5. ### nfshp253

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can you tell me where i can adjust the control points?

6. ### zaxxon

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292
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Right click on a node.
Select "Smooth Selected Nodes->Control Points"

Now you should see the control points. Click on them and drag to modify their position.

7. ### nfshp253

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I don't have that option. I only have "By Height" or "Flatten"

8. ### zaxxon

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292
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Create again the track, and do NOT just click to define the nodes, DRAG a little bit.

9. ### nfshp253

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Drag? Nothing happens. Am I suppose to create a closed loop track?

10. ### zaxxon

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I don't understand. You want a closed loop track, don't you?

11. ### nfshp253

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Yes. But I can click and drag to define nodes. The nodes only show if I click! Can you upload your saved circle instead?

12. ### zaxxon

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Put these files inside the My Projects folder and open the project

http://www.sendspace.com/file/6bquxq

13. ### nfshp253

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Thanks! But can you help me figure out how adjust entry and exit distances. I'm using the newest version anyway. So is there any difference?

14. ### zaxxon

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292
Ratings:
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With version 0.7 you can adjust them graphically.
On the first 10 seconds of this video you can see how the control points
are set when creating the track (drag the mouse).

You can edit the file Venue.xml I sent to you and set there the control
points with more accuracy

15. ### banger

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661
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click and drag the mouse , don't let the button go. then you will see the control nodes.release when finished

16. ### Lee Knight

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Gday zaxxon,
Ive seen a photo of a 'magic round-about' (7round-abouts layed out around a larger one!:eek that I wish to build for a playground for cars.
Unfortunately, Im a noob & my efforts so far to make perfect circles have been greatly let down by my skills but this would go a long way to getting me started.
I doubt it'll ever be released, (more an experiment & a laugh really) but if Im successful I'd send a copy back to you....
BLeeK

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765
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A circle, are you joking guys ?

Just trigger 'Bezier Curve' in options, align/each CP (control point) to the grid (a cross shape in a cube) & ALIGN the 4 CP tangents to the grid (X/Y axis from top view). You're done, only with 4 CPs, a perfect circle is created. Since you know the grid distances, you can adjust quickly your scaling & get your precise length.

18. ### Lee Knight

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Thank You AGAIN ehrlec!
I tried the .csv but couldn't get it to work for me....
Ive never used .csv data before, just .kml
I'll let you know if I manage to make myself dizzy!:wink:
THANK YOU!