[GIS] How are section of roads uniquely identified (in both directions) by Google Maps

database-designgoogle mapsmappingroad

I am wondering whether roads around the world are uniquely identified by a certain value in Google Maps? If so, are they mapped uniquely in terms of their direction? i.e is route A to B is identified differently from route B to A?

In general, I am looking at how the backend database would be structured in terms of uniquely identifying a road, and also if they split it into the two different directions.

Since I don't really know most of the maps, I guess to narrow down the scope any example would work else just take it that I am asking about how Google Maps does it!

Best Answer

From the Google Maps Maker Maker Help page:

Lanes designate the number of vehicles that can pass parallel to one another on the route. Select the number of lanes to specify the total number of drivable lanes on the drawn road. Verify the number of lanes selected using satellite imagery and Street View where available.

One-way Roads: Use the total number of lanes present on the road.

Undivided Two-way Roads: If traffic is travelling in both directions, use the total number of lanes on both sides of the road.

Split Roads: If the road is split into two separate segments due to a physical or painted median, the Lanes attribute should be set separately for each side of the road.

Note: Some road segments may act as funnels, causing the total number of lanes to increase or decrease along the length of the segment. Use the total lanes at the narrowest part of the segment. For example, a ferry dock entrance road may have 10 or more lanes at its widest point, but decrease to 3 lanes at its narrowest point - so the road would have a lane count of 3.

...

The Direction describes how automobile traffic flows on the road. In the US, vehicles travel in the right-hand lane, whereas the opposite is true in places such as India and the United Kingdom. Select from the following Directions:

No traffic: This should not be used for any restrictions on a road.

Two-way: Road that supports two-way traffic (bi-directional traffic).

One-way (A to B) / One-way (B to A): Road that supports traffic in a single direction. Select A to B or B to A based on the direction of traffic flow. The A and B markers refer to the endpoints of the road on the map. Use Street View and satellite imagery when possible to verify the direction of travel.

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[GIS] Interpolate points between coordinates for smooth animation in google maps or openmap

You have a variety of strategies -- in general, you can think of your points as a set of constraints: at time t, the displayed point must be at (x,y) on the screen. What happens between constrained times is up to you. ;)

Note: I'm assuming that you're interested in interpolating on the plane -- that is, you're not doing airplane routes (or other long distances) that must be great circles.

The simplest interpolation is linear: Between points p0 and p1 at times t0,t1 respectively, you can generate the point p for any time between t by:

dt = (t - t0) / (t1 - t0) // fraction of time elapsed between t0 & t1
p.x = p0.x + ( dt * (p1.x - p0.x) )  // the point's x is that same fraction between x0 and x1
p.y = p0.y + ( dt * (p1.y - p0.y) )  // ditto, y.

However, there's a lot of complication you can add, if you want to make things even "smoother". Some examples:

Constrain and interpolate travel speed as well as position.
Ditto, velocity vectors (that also incorporate direction of travel as well as speed -- this is how bezier curves work, by the way).
Easing, which is a nonlinear transformation of 'dt' -- lets animations e.g. accelerate at the beginning and decelerate at the end.

[GIS] Data from google maps or bing maps available for offline use? Whole cities, I mean

When you say download, I assume you mean for free. You may be able to find something here http://gis-lab.info/qa/vmap0-eng.html which will be good enough for testing.

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[GIS] Data from google maps or bing maps available for offline use? Whole cities, I mean

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