Perfect Straights in Bob's Track Builder

In Bob's Track Builder it's easy to make a smooth flowing track, but there are times when things need to be perfectly straight. See also: Constant Radius Corners in Bob's Track Builder

This tutorial will show you how to make straights that are perfectly straight. Or as close as possible with the tools available.

Step 1: Set up the straight.

Assuming you've already built your track, you'll need to ensure there is a node at the start of the straight, and another node at the end.* For a section of track that is perfectly straight between nodes A and B, the exit control point of node A must point directly at node B, and the entry control point of node B must point directly at node A:

In the above image you can see that they aren't quite lined up. You could keep adjusting the control points, but in order to get the necessary fine control, you have to zoom in, and then you can't see other other node.

*You may have several nodes along the straight to create hills and dips, but for now, two nodes are enough.

Step 2: Build a genuinely straight track

Create a new open ended track open_track.gif with just 2 nodes (press Escape after adding the second one).


This optional step will show you what happens.
Move the nodes of the open track so that it has a noticeable curve. Select both nodes, and right-click in the top view. From the menu, select "Smooth Selected Control Points > All Directions". You will see the following transformation:
st2.gif st3.gif
This has made the track perfectly straight. It won't work with the nodes of your main track because it has other nodes before and after the straight.

Step 3: Align the nodes

Select the first node of the open track, hold down M, and drag it towards the node at the beginning of the straight:
Node C will snap to the position of node A.

Move the second node of the open track to the end of the straight of the main track:
Node D will snap to node B.

Step 4: Straighten the open track

Select the two nodes (C and D). Right click in the top view, and select "Smooth Selected Control Points > All Directions". This makes the second track perfectly straight:

Step 5: Compare the two straights

Zoom in around the middle of the straight. If the main track has a perfect straight, you won't see any difference. More likely you'll see this:
The blue track is the main one, and the red track is the perfect straight.

Step 6: Correct the main straight

Move the two circled control points so that they line up with the centreline of the open track:
st9.gif st10.gif

Now the main straight really is a straight.

Step 7: Using extra nodes

A straight with bumps and dips may have extra nodes, but the straightening technique is very similar.

  • The open track still only needs just two nodes (otherwise it cannot be made perfectly straight).
  • Follow steps 1, 2 and 3.

Let's say the straight has 4 nodes:

  • Line up the exit control point of node 1 with the middle of the open track
  • Move node 2 so that it's over the middle of the open track.
  • Line up the entry control point of node 2 with the middle of the open track.
  • Line up node 3 with the middle of the open track
  • Line up the entry control point of node 3
  • Line up the entry control point of node 4

Now you should be able to make perfect straights.

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