Tuesday, February 28, 2012

Borders, sides, barriers

Well, after 'some' silence - and renaming the blog - let me share what I'm fiddling with these days.

I'd like to build a track that models a temporary endurance track, using a standard, 2 * (2+1) lane motorway somewhere in Europe. That is, 2 lanes for normal traffic and one emergency lane, in both directions. There are some chicanes put up using huge plastic piles, a U-turn to turn onto the same motorway but the other side (other direction), a bridge, etc...
Problem comes when you want to build it in Speed Dreams so that it looks great and works correct, too. Why? Here's a brief introduction.


Tracks in Speed Dreams

In Speed Dreams' track format, you are given arbitrary length track segments, that have:
  • width
  • 2 borders (left and right)
  • 2 sides (left and right) and
  • 2 barriers (left and right).
The width is static, so you define the 'track width' at the beginning of the track description and it does not change from then. It is a limit very hard to live with and we aim to get it changed sometime soon.
The borders are fixed width along each segment, but can change width on the next segment. The border also has 'height', that is the height of the border's outer side - just think of curbs on racetracks and you'll get the picture. If you set height to 0, it will be flat of course.
Here comes the side - that should be the side of the track, like the grass next to the concrete strip on a racetrack. The side can change width linearly from the start to the end for each segment, so you can define  narrow or wide areas next to the tracks easily.
The barriers mean the physical edge of our tracks. There is no life outside the barrier on a Speed Dreams track - this is that farthest you can wander from the track. We use this to put up walls, fences, armco around the track.
Well if you happen to use a 3D editor to change the track's landscape, you can of course define any scenery wwwwwaaaay behind the barrier, but that is only eye-candy - you cannot enter that realm with your car.
Obligatory picture just to make all the lines above useless

All of the above is much better described in Andrew's tutorial, worth checking out.


Chicane ahead!

Now back to the original problem. At first you'd think there is nothing simpler than modelling a motorway: set track width to 3 lanes's width (which I've googled to be 3 * 3.75m usually for Europe), set some 50cm border to mark the transition from asphalt to grass, then use 2 metres of grass on the inside and 20m on the outside, then set up a fence as barrier and you are done.
But we want chicanes to slow the cars down a bit before a U-turn! So technically speaking, the track is about 1.5-2 lanes wide only, goes from one edge of the 3 lanes to the other edge when entering or exiting the chicane. Still we want to use the 'side' for the grass areas and we must have barriers, too:
Motorway with chicanes and the racingline cars will most likely follow

That means we need borders that change their width along the segment's length. In Speed Dreams, our robots use the borders or the sides without any fear, if they seem to be 'good' for driving. So if you set the surfaces of the borders the same as the track, the robots will use the borders when chosing their racing line. If you set the side's surface the same, the robots will drive on the sides, too - but set it to some bumpy or grippy or slippery and the robots will keep away from it. That is ideal for us in this situation, we can use the borders as asphalt and the sides as grass.


Digital technique

Now let's see our next picture:
Digital magic

Sadly enough, borders cannot change width currently, so we have to use a trick somehow. This is what I'm trying now: whenever there is need, I cut the track segment into short pieces (quantate it...), see the ugly lilac lines. Every short segment will have a border with different width (gray lines, black distance markers), this is how I emulate the border width changing. In fact, it is changing, not continuosly but step-by-step, like when you digitize an analogue value (quantate then sample average for the segment).
This is a dirty trick indeed and looks awful when you produce the track and try it in the simulator. However, Speed Dreams uses the track description only to make the cars know where to drive - what you see is a completely different story. The visuals can be edited in a 3D editor like Blender or AC3D and we can get rid of all the jigged borders there. Likewise, you could build a track on an iced lake completely covered with ice and only signposts to signal the track, or in a desert with camels showing the limits...


Does it work?

Soon I'll tell you if I've succeeded or not.
BTW did you like my 6-year-old-level graphics? This is our new toy in the family, a Bamboo table & pen - actually my daughter got it as a birthday present and she can draw beautiful drawings using it. Her dad obviously is not able to do the same :)

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