Calculation of unlit_factor

[ChenW12]

Hi,

I am quite curious about the calculation of the unlit_factor. Is there any story behind it? What if unlit_factor_ = unlit_factor + 1.f is used?

valhalla/src/sif/dynamiccost.cc

Lines 365 to 368 in 6fbe96e

	void DynamicCost::set_use_lit(float use_lit) {
	unlit_factor_ =
	use_lit < 0.5f ? kMinLitFactor + 2.f * use_lit : ((kMinLitFactor - 5.f) + 12.f * use_lit);
	}

Thank you

[chrstnbwnkl]

Yeah there was a discussion about it when it was introduced in #3957 . The idea was to convert the use_lit value (a float between 0 and 1) into a cost factor in a way that does not impact costing when use_lit == 0, and also has a stronger impact when use_lit > 0.5.

[ChenW12]

Thank you so much for answering! I am trying to introduce a new factor about crime rate. Is there a preferred range for a factor (like the range of unlit_factor is [1,8])?

[chrstnbwnkl]

It really depends on what you want to achieve. With unlit_factor the idea was not too exaggerate the factor too much, since it would not be very sensible to have a huge detour on a route just to get a few meters of lit road. As stated in the API reference a factor can take a max value of 100000, so there's lots of room, but whether or not you need it is completely use case dependent.

[ChenW12]

Thank you so much for the response! I understand it now!