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<ol class="chapter"><li class="chapter-item expanded "><a href="../index.html"><strong aria-hidden="true">1.</strong> Overview</a></li><li class="chapter-item expanded "><a href="../howto/index.html"><strong aria-hidden="true">2.</strong> Instructions</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../howto/dev.html"><strong aria-hidden="true">2.1.</strong> Developer guide</a></li><li class="chapter-item expanded "><a href="../howto/map_parking.html"><strong aria-hidden="true">2.2.</strong> How to map on-street parking</a></li><li class="chapter-item expanded "><a href="../howto/new_city.html"><strong aria-hidden="true">2.3.</strong> Importing a new city</a></li><li class="chapter-item expanded "><a href="../howto/misc_dev_tricks.html"><strong aria-hidden="true">2.4.</strong> Misc developer tricks</a></li></ol></li><li class="chapter-item expanded "><a href="../how_it_works.html"><strong aria-hidden="true">3.</strong> How it works</a></li><li class="chapter-item expanded "><a href="../map/index.html" class="active"><strong aria-hidden="true">4.</strong> Map model</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../map/importing/index.html"><strong aria-hidden="true">4.1.</strong> Importing</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../map/importing/convert_osm.html"><strong aria-hidden="true">4.1.1.</strong> convert_osm</a></li><li class="chapter-item expanded "><a href="../map/importing/geometry.html"><strong aria-hidden="true">4.1.2.</strong> Road/intersection geometry</a></li><li class="chapter-item expanded "><a href="../map/importing/rest.html"><strong aria-hidden="true">4.1.3.</strong> The rest</a></li></ol></li><li class="chapter-item expanded "><a href="../map/edits.html"><strong aria-hidden="true">4.2.</strong> Live edits</a></li><li class="chapter-item expanded "><a href="../map/misc.html"><strong aria-hidden="true">4.3.</strong> Misc</a></li></ol></li><li class="chapter-item expanded "><a href="../trafficsim/index.html"><strong aria-hidden="true">5.</strong> Traffic simulation</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../trafficsim/discrete_event.html"><strong aria-hidden="true">5.1.</strong> Discrete event simulation</a></li><li class="chapter-item expanded "><a href="../trafficsim/travel_demand.html"><strong aria-hidden="true">5.2.</strong> Travel demand</a></li><li class="chapter-item expanded "><a href="../trafficsim/gridlock.html"><strong aria-hidden="true">5.3.</strong> Gridlock</a></li></ol></li><li class="chapter-item expanded "><a href="../case_studies/index.html"><strong aria-hidden="true">6.</strong> Case studies</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../case_studies/lake_wash.html"><strong aria-hidden="true">6.1.</strong> Lake Washington Blvd Stay Healthy Street</a></li><li class="chapter-item expanded "><a href="../case_studies/west_seattle.html"><strong aria-hidden="true">6.2.</strong> West Seattle mitigations</a></li></ol></li><li class="chapter-item expanded "><a href="../api.html"><strong aria-hidden="true">7.</strong> API</a></li><li class="chapter-item expanded "><a href="../project/index.html"><strong aria-hidden="true">8.</strong> Project</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../project/roadmap.html"><strong aria-hidden="true">8.1.</strong> Roadmap</a></li><li class="chapter-item expanded "><a href="../project/motivations.html"><strong aria-hidden="true">8.2.</strong> Motivations</a></li><li class="chapter-item expanded "><a href="../project/history/index.html"><strong aria-hidden="true">8.3.</strong> History</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../project/history/backstory.html"><strong aria-hidden="true">8.3.1.</strong> Backstory</a></li><li class="chapter-item expanded "><a href="../project/history/year1.html"><strong aria-hidden="true">8.3.2.</strong> Year 1</a></li><li class="chapter-item expanded "><a href="../project/history/year2.html"><strong aria-hidden="true">8.3.3.</strong> Year 2</a></li><li class="chapter-item expanded "><a href="../project/history/year3.html"><strong aria-hidden="true">8.3.4.</strong> Year 3</a></li></ol></li><li class="chapter-item expanded "><a href="../project/CHANGELOG.html"><strong aria-hidden="true">8.4.</strong> Full CHANGELOG</a></li><li class="chapter-item expanded "><a href="../project/references.html"><strong aria-hidden="true">8.5.</strong> References</a></li></ol></li></ol>
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<h1 class="menu-title">A/B Street</h1>
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<main>
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<h1><a class="header" href="#map-model" id="map-model">Map model</a></h1>
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<p>A/B Street builds a rich representation of a city map using OpenStreetMap (OSM) and other sources. This chapter describes how.</p>
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<p>TODO: Integrate pictures from
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<a href="https://docs.google.com/presentation/d/1cF7qFtjAzkXL_r62CjxBvgQnLvuQ9I2WTE2iX_5tMCY/edit?usp=sharing">these slides</a>.</p>
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<p><a href="https://youtu.be/chYd5I-5oyc?t=439">This recorded presentation</a> covers some of
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this.</p>
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<h2><a class="header" href="#the-map" id="the-map">The map</a></h2>
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<p>A single city is broken down into different pieces...</p>
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<p>A/B Street comes with a few maps, each defined by a bounding/clipping polygon
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for some portion of Seattle. Each map has these objects:</p>
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<ul>
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<li><strong>Roads</strong>: A single road connects two intersections, carrying OSM metadata and
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containing some child lanes.</li>
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<li><strong>Lanes</strong>: An individual lane of traffic. Driving (any vehicle), bus-only, and
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bike-only lanes have a direction. On-street parking lanes don't allow any
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movement, and they have some number of parking spots. Sidewalks are
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bidirectional.</li>
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<li><strong>Intersections</strong>: An intersection has references to all of the incoming and
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outgoing lanes. Most intersections have a stop sign or traffic signal policy
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controlling movement through it.
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<ul>
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<li><strong>Border</strong> intersections on the edge of the map are special places where
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agents may appear or disappear.</li>
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</ul>
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</li>
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<li><strong>Turns</strong>: A turn connects one lane to another, via some intersection.
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(Sidewalks are bidirectional, so specifying the intersection is necessary to
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distinguish crosswalks at each end of a sidewalk.)</li>
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<li><strong>Buildings</strong>: A building has a position, OSM metadata, and a <strong>front path</strong>
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connecting the edge of the building to the nearest sidewalk. Most trips in A/B
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Street begin and end at buildings. Some buildings also contain a number of
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off-street parking spots.</li>
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<li><strong>Area</strong>: An area has geometry and OSM metadata and represents a body of
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water, forest, park, etc. They're just used for drawing.</li>
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<li><strong>Bus stop</strong>: A bus stop is placed some distance along a sidewalk, with a
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pointer to the position on the adjacent driving or bus lane where a bus stops
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for pick-up.</li>
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<li><strong>Bus route</strong>: A bus route has a name and a list of stops that buses will
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cycle between. In the future, they'll include information about the
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frequency/schedule of the route.</li>
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<li><strong>Parking lot</strong>: A parking lot is connected to a road, has a shape, and has
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some internal driving "aisles." The number and position of individual parking
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spots is auto-generated.</li>
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</ul>
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<h2><a class="header" href="#coordinate-system" id="coordinate-system">Coordinate system</a></h2>
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<p>A/B Street converts (longitude, latitude) coordinates into a simpler form.</p>
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<ul>
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<li>An (x, y) point starts with the top-left of the bounding polygon as the
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origin. Note this is screen drawing order, not a Cartesian plane (with Y
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increasing upwards) -- so angle calculations account for this.</li>
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<li>The (x, y) values are f64's trimmed to a few decimal places, with way more
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precision than is really needed. These might become actual fixed-point
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integers later, but for now, a <code>Pt2D</code> skirts around Rust's limits on f64's by
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guaranteeing no NaN's or infinities and thus providing the full <code>Eq</code> trait.</li>
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<li>A few places in map conversion compare points using different thresholds,
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usually below 1 meter. Ideally these epsilon comparisons could be eliminated
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in favor of a fixed-point integer representation, but for now, explicit
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thresholds are useful.</li>
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</ul>
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<h2><a class="header" href="#invariants" id="invariants">Invariants</a></h2>
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<p>Ideally, the finalized maps would satisfy a list of invariants, simplifying the
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traffic simulation and drawing code built on top. But the input data is quite
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messy and for now, most of these aren't quite guaranteed to be true.</p>
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<ul>
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<li>Some minimum length for lanes and turns. Very small lanes can't be drawn, tend
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to break intersection polygons, and may lead to gridlocked traffic.</li>
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<li>Some guarantees that positions along adjacent lanes actually match up, even
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though different lanes on the same road may have different lengths. Examples
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include the position of a bus stop on the sidewalk and bus lane matching up.
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<ul>
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<li>Additionally, parking lanes without an adjacent driving lane or bus stops
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without any driving or bus lanes make no sense and should never occur.</li>
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</ul>
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</li>
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<li>Connectivity -- any sidewalk should be reachable from any other, and most
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driving lanes should be accessible from any others. There are exceptions due
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to border intersections -- if a car spawns on a highway along the border of
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the map, it may be forced to disappear on the opposite border of the map, if
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the highway happens to not have any exits within the map boundary.</li>
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</ul>
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<h2><a class="header" href="#connectivity" id="connectivity">Connectivity</a></h2>
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<p>For a single mode, each lane is connected to two intersections. Turns connect
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two lanes. There are no turns between sidewalks and driving/bike/bus lanes.</p>
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<p>All buildings and parking lots have driveways. This must connect to a sidewalk,
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allowing pedestrians to enter/exit that object. The driveway OPTIONALLY
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connects to the nearest driveable lane. This allows cars to enter/exit that
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object for parking.</p>
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<p>Public transit stops are located somewhere on a sidewalk. They're associated
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with a driveable position where the bus or train stops. In the future, this
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will need to account for dedicated surface-level platforms and for underground
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transit stations, likely associated with a building.</p>
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<p>There's a concept of "parking blackholes." If you treat every road as
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bidirectional without access restrictions, then the graph is connected. But the
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more detailed view has to factor in one-way roads and things near the map
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border. These blackholes influence where cars will try to look for parking
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(since we don't want them entering a blackhole and getting stuck) and also, for
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temporary/unintentional reasons, where pedestrian<->bicycle transitions will
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happen.</p>
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