openplans/OpenTripPlanner — Issue #560: avoid starting search in unsafe place
Author: andrewbyrd
Created: 2011-11-09 18:59:06+00:00
State: open

During a check-in call we discussed the problem of searches starting/ending in areas from which one cannot safely access transit on foot/bike.

There are two cases here:
1) The user actually really wants to start in a place from which you cannot safely access transit. This causes the search to fail, and an appropriate error message is given.
2) The closest road to where the user clicked in his/her client app does not allow safely reaching transit, but this road was really arbitrarily chosen because the client map is zoomed out to where individual roads are not easily distinguishable.

The solution may be to start the search in several places at once, eg all roads within a certain specific radius of where the user clicked. However, if all these start points are enqueued with 0 initial weight, paths originating at the start point farthest from where the user clicked are likely to dominate. These alternate starting points should therefore be enqueued with a weight greater than a reasonable estimate of walking cost from the principal search start point.

This method would require the client to provide the server with both a start point and a 'radius of ambiguity'. The client can then account for input methods and the display resolution of the device it is running on.

This ticket is related to #559 and should also be addressed when multi-objective searching is stable.