abstreet/geometry.md at a1176e053bbc407e6455b8ee0bfdf38b4790a667

mirror of https://github.com/a-b-street/abstreet.git synced 2024-12-29 17:34:58 +03:00

Dustin Carlino 260a2bdc3d forming the intersection polygon by the expected adjacency order, not by blindly sorting points by angle from a center. seems to fix some problems in merged mode!

2019-02-06 11:49:45 -08:00

Intersection geometry brainstorm

can we merge adjacent polylines at intersections based on closest angle, and then use the existing stuff to get nice geometry?
- i think we still have to trim back correctly
- first figure out all the trimming cases for the T, outside and inside lanes, etc
before trimming back lines, project out the correct width. sort all those points by angle from the center. thats the intersection polygon? then somehow trim back lines to hit that nicely.
do the current trim_lines thing, but with lines, not segments? no, there'd be many almost-parallel lines.
at a T intersection, some lines aren't trimmed back at all
https://www.politesi.polimi.it/bitstream/10589/112826/4/2015_10_TOPTAS.pdf pg38
just make polygons around center lines, then intersect?

morning thoughts!

trim lines based on outermost POLYGON border line, not lane center lines or anything
the ascending angle and skipping existing lines in the thesis seems to make sense
find where infinite line intersects line segment for some cases?

Problems right now:

i28: on a simple 4-way, sidewalk polygons both overlap and leave a little bit of gap space
- fig1: could trim back, but would want to later add back the corners for sidewalks.
- fig2: embrace overlap of sidewalks at corners
  - dont worry about agents on sidewalks overlapping
- just draw entire block's curb, just for rendering, not logical center sidewalk lines?
  - TODO check sources to see if any have this
i52: on a 4-way at a slant, road endings are very jagged
thoughts on trim lines
- need to run it in playground step-by-step
- fig 3: almost want to think about matching up equivalent lanes on adjacent half-roads
  - trim adjacent sidewalks, then adjacent parking lanes, ...
  - but maybe this looks very weird, and sidewalks are the exception

afternoon idea:

start with entire roads and the giant thick polygons
just find the intersection of all those big polygons
almost like a loop:
- trim back yellow center lines, compute giant road band, see if there's intersection
- then figure out the lane geometry WITHIN the constraint of the big road band
probably doesnt have to be a fixed point loop. what if we just trim lines based on the outermost lines of all the roads? and then based on how much length we removed there, reduce the original yellow center lines. at some angles this is exactly the same. at others, it's probably different -- is there a specific relation we can figure out?

Not aiming to get it right forever, just improving the mess now.

Pt2D
- just a pair of f64's, representing world space (non-negative)
- no more ordered_float; have a variant only when needed
Angle
- normalized, with easy reversing/perpendicularing
Line
- pair of points
Polyline
Polygon