### Author Topic: Geometary question  (Read 18766 times)

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#### jamespetts

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##### Re: Geometary question
« Reply #35 on: October 14, 2015, 08:48:37 PM »
It is not the fact of points that limit speed, but the fact of diverging at an angle and there therefore being a sharp turn: this is why it is common for signalling to give an indication to a train of the route that it is to take so that the driver knows the speed: even where, for example, the main and relief lines both have speed limits of 160km/h or 110km/h, the speed limit for crossovers between the two might be closer to 50km/h (especially in earlier times where very large radius points had not been developed).

As for (b), this might apply to trains that are stopping at stations, but not to those passing through, which generally pass at line speed. (e) is not uncommon in the games that I have seen, at least where track passes through built up or mountainous (or even mildly hilly) areas, and it is often necessary to slew to avoid crossing a river at a junction of a tributary or a bend.

#### Ters

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##### Re: Geometary question
« Reply #36 on: October 14, 2015, 09:39:27 PM »
It seemed very clear to me that you did not seriously consider to start coding and replace the tile based system simutrans uses with a system using some free-form curves, e.g., splines. But rather that you offered it as a way of how speed limits for complicated bends could be properly evaluated. In contrast to the current system where it would be nearly hopeless because of some reasons you gave in detail.

Almost. I was using it as a yardstick for how much work I think it will be to implement what I wrote about earlier in the post. That they could be so close, that one (almost) might as well go for the real thing.

#### isidoro

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##### Re: Geometary question
« Reply #37 on: October 15, 2015, 12:02:33 AM »
Regarding Sarlock's "straight" lines:

It's all a question of scale, I think.  A mathematical algorithm can only possible see what comes out from the data you input to it.  In order to detect "straight" lines like Sarlock's, you have to give "a few" tiles before and "a few" tiles after the point in question.  How many is "a few"?  That's the question.

For straight, one tile.  For 45, two tiles, etc.

But I'm with James that it makes little sense, at least to me, to consider those things "straight" if you can have trains much smaller than the number of tiles to detect those "straight" lines.

And that also applies to the algorithm some of us have proposed above (mine too), how can a train "sense" a big, big 90 degree curve if she isn't long enough to be in the two 45 degree turns at the same time?