I have a map with about 80 annotations. I would like to do 3 things.
1) From my current location, I would like to know the actual route distance to that position. Not the linear distance.
2) I want to be able to show a list of all the annotations, but for every annotation (having lon/lat) I would like to know the actual route distance from my position to that position.
3) I would like to know the closest annotation to my possition using route distance. Not linear distance.
I think the answer to all these three points will be the same. But please keep in mind that I don't want to create a route, I just want to know the distance to the annotation.
I hope someone can help me.
Best regards,
Paul Peelen
From what I understand of your post, I believe you seek the Haversine formula. Luckily for you, there are a number of Objective-C implementations, though writing your own is trivial once the formula's in front of you.
I originally deleted this because I didn't notice that you didn't want linear distance at first, but I'm bringing it back in case you decide that an approximation is good enough at that particular point of the user interaction.
I think as pointed out before, your query would be extremely heavy for google maps API if you perform exactly what you are saying. Do you need all that information at once ? Maybe first it would be good enough to query just some of the distances based on some heuristic or in the user needs.
To obtain the distances, you could use a Google Maps GDirections object... as pointed out here ( at the bottom of the page there's "Routes and Steps" section, with an advanced example.
"The GDirections object also supports multi-point directions, which can be constructed using the GDirections.loadFromWaypoints() method. This method takes an array of textual input addresses or textual lat/lon points. Each separate waypoint is computed as a separate route and returned in a separate GRoute object, each of which contains a series of GStep objects."
Using the Google Maps API in the iPhone shouldn't be too difficult, and I think your question doesn't cover that, but if you need some basic example, you could look at this question, and scroll to the answer.
Good Luck!
Calculating route distance to about 80 locations is certain to be computationally intensive on Google's part and I can't imagine that you would be able to make those requests to the Google Maps API, were it possible to do so on a mobile device, without being severely limited by either the phone connection or rate limits on the server.
Unfortunately, calculating route distance rather than geometric distance is a very expensive computation involving a lot of data about the area - data you almost certainly don't have. This means, unfortunately, that this isn't something that Core Location or MapKit can help you with.
What problem are you trying to solve, exactly? There may be other heuristics other than route distance you can use to approximate some sort of distance ranking.
Related
How can I get speed limit for multilevel intersections/roads? When I go over the bridge or under the bridge, I can get wrong speed limit.
I am using: way[maxspeed](around:20, <latitude>, <longitude>), but I cannot specific altitude.
I am using Overpass API by OpenStreetMaps.
Unfortunately, your current approach of considering speed limits of any road within a certain radius around your location is likely to struggle not just at multilevel intersections, but also with parallel roads and at regular intersections involving ways with different speed limits. It assumes that you know your location with an accuracy that you won't have available in many use cases, and fails in 3 dimensions because OpenStreetMap data does not contain altitude information, only a vertical ordering (i.e. whether an object is above or below another).
It seems to me that the problem you need to solve is finding out which road you're actually on. Once you know the road, you can easily access any of its attributes, including those relevant to speed limits.
This problem of finding the corresponding road for a location, and preferably a history of past locations, is called map matching. For OpenStreetMap data, I believe GraphHopper offers a map matching implementation and API.
I would like to calculate a graph similiar to an isochrone using pgsql. Therefore, I already used the algorithm pgr_drivingDistance. You provide a starting point and a distance value and receives an isochrone.
The output using the algorithm is received with code which looks something like:
SELECT * FROM pgr_drivingDistance(
'SELECT id, source, target, cost FROM edge_table',
2, 2, false -- starting point, distance, directed
);
The red star represents the starting point.
Now, I want a graph which works the same way, like starting at one point and get routes in all directions. The difference is, that I don't want to provide a travel distance, but a list with point coordinates, which are lying on the road network. The route in every direction has to stop at the first reached point lying on each route. The distance on every route is different and I don't know which points are the closest ones.
The desired output using the "stopping" points, which are visualized in green, is supposed to look like this.
I tried already:
Using the given algorithm pgr_drivingDistance and raising the distance value every time no point is reached -> problem here: the distance is equal for all directions and not individual for each route.
Using the algorithm pgr_dijkstra for each route -> problem here: because you don't know which point is affected you don't know which end point to choose for the calculation. You also cannot take the closest one in the immediate vicinity because you need the closest one on the specific route.
I know that I have to build an almost complete new algorithm, but maybe someone has an idea how to start or even experience with this kind of problem.
Thank you in advance!
This is a one to many routing problem. You have to compute the route to each end point to find the shortest one. I have not looked at the pgRouting function recently, but I believe there is a one to many, many to one and many to many Dijkstra function(s). You should be able to use the one to many to compute all the routs in one go and then you can sort the routs based on length to find the shortest one.
I want to calculate a route from A to B using only a subset of the routes available in a city, as long as it is possible (if A or B is not on the subset of roads I still need to calculate the route). I tried to use avoidareas but it's quite difficult to define rectangles to avoid outside of the roads (and I saw somewhere the number of boxes is limited).
Can you please explain what do you mean by "subset of the routes". Do you mean to avoid a particular kind of road?
if you want to always include a certain road(s) you can always use waypoints to direct the route through those roads. Generally, Routing algorithms are designed to "avoid" not "prefer" an area.
Various examples on how to avoid a rectangle(s) is explained here- https://developer.here.com/documentation/routing/topics/example-route-avoiding-an-area.html
How to use a waypoint is explained here - https://developer.here.com/documentation/routing/topics/resource-param-type-waypoint.html
How to avoid a certain road type is explained here - https://developer.here.com/documentation/routing/topics/avoiding-certain-road-types.html
I am implementing an app which measures the how much distance it has moved .For example if my device felldown from my table to ground ,then I would like to calculate the distance.So Kindly help me to do this. Let me know if my question is not clear.
Thanks in advance.
Your question is very clear : you want to compute the second level integral of the acceleration, which theorically is possible, by supposing the speed null at some time, but I really doubt you could get something precise enough to make any sense (as in many integral computations).
This isn't done today because the error is too big. Done in hardware (for permanent integration of the acceleration) it could be a little more precise but probably not enough to really compute a distance in any acceptable sense of the word "accuracy".
If you want to try it by yourself, here's a document describing more in detail the approach : http://perso-etis.ensea.fr/~pierandr/cours/M1_SIC/AN3397.pdf
It is possible to easily use the GPS functionality in the iPhone since sdk 3.0, but it is explicitly forbidden to use Google's Maps.
This has two implications, I think:
You will have to provide maps yourself
You will have to calculate the shortest routes yourself.
I know that calculating the shortest route has puzzled mathematicians for ages, but both Tom Tom and Google are doing a great job, so that issue seems to have been solved.
Searching on the 'net, not being a mathematician myself, I came across the Dijkstra Algorithm. Is there anyone of you who has successfully used this algorithm in a Maps-like app in the iPhone?
Would you be willing to share it with me/the community?
Would this be the right approach, or are the other options?
Thank you so much for your consideration.
I do not believe Dijkstra's algorithm would be useful for real-world mapping because, as Tom Leys said (I would comment on his post, but lack the rep to do so), it requires a single starting point. If the starting point changes, everything must be recalculated, and I would imagine this would be quite slow on a device like the iPhone for a significantly large data set.
Dijkstra's algorithm is for finding the shortest path to all nodes (from a single starting node). Game programmers use a directed search such as A*. Where Dijkstra processes the node that is closest to the starting position first, A* processes the one that is estimated to be nearest to the end position
The way this works is that you provide a cheap "estimate" function from any given position to the end point. A good example is how far a bird would fly to get there. A* adds this to the current distance from the start for each node and then chooses the node that seems to be on the shortest path.
The better your estimate, the shorter the time it will take to find a good path. If this time is still too long, you can do a path find on a simple map and then another on a more complex map to find the route between the places you found on the simple map.
Update
After much searching, I have found an article on A* for you to to read
Dijkstra's algorithm is O(m log n) for n nodes and m edges (for a single path) and is efficient enough to be used for network routing. This means that it's efficient enough to be used for a one-off computation.
Briefly, Dijkstra's algorithm works like:
Take the start node
Assign it a depth of zero
Insert it into a priority queue at its depth key
Repeat:
Pop the node with the lowest depth from the priority queue
Record the node that you came from so you can track the path back
Mark the node as having been visited
If this node is the destination:
Break
For each neighbour:
If the node has not previously been visited:
Calculate depth as depth of current node + distance to neighbour
Insert neighbour into the priority queue at the calculated depth.
Return the destination node and list of the nodes through which it was reached.
Contrary to popular belief, Dijkstra's algorithm is not necessarily an all-pairs shortest path calculator, although it can be adapted to do this.
You would have to get a graph of the streets and intersections with the distances between the intersections. If you had this data you could use Dijkstra's algorithm to compute a shortest route.
If you look at technology tomtom calls 'IQ routes', they measure actual speed and travel time per roadstretch per time of day. This makes the arrival time more accurate. So the expected arrival time is more fact-based http://www.tomtom.com/page/iq-routes
Calculating a route using the A* algorithm is plenty fast enough on an iPhone with offline map data. I have experience of doing this commercially. I use the A* algorithm as documented on Wikipedia, and I keep the road network in memory and re-use it; once it's loaded, routing even over a large area like Spain or the western half of Canada is practically instant.
I take data from OpenStreetMap or elswhere and convert it into a directed graph, assuming (which is the right way to do it according to those who know) that any two roads sharing a point with the same ID are joined. I assign weights to different types of roads based on expected speeds, and if a portion of a road is one-way I create only a single arc; two-way roads get two arcs, one in each direction. That's pretty much the whole thing apart from some ad-hoc code to prevent dangerous turns, and implementing routing restrictions.
This was discussed earlier here: What algorithms compute directions from point a to point b on a map?
Have a look at CloudMade. They offer a free service for iPhone and iPad that allows navigation based on your current location. It is built on open street maps and has some nifty features like making your own mapstyle. It is a little slow from time to time but its totally free.