I learned that Google Map has a Get Direction feature that let users find the shortest path from one point to another. What search algorithm did Google used for this search? Is this algorithm can be implemented in the Android platform, knowing that it has low memory and it's running in Java(tend to be slow)? Thanks in advance!
It is very likely that they use either A* (A-star) or dijkstra's algorithm.
Comparing the two, A* uses less memory and thus is more likely that they use a hybrid of that.
Related
I wish to make an android app that leverages OSM services and runs an algorithm of my choice to find the route, say A* or some heuristic on Dijkstra.
The Routing wiki page of OSM has some good pointers but it does not give any insight about how to go about implementing your own algorithm in the app.
This response is overview which might help you to orient better in the landscape and find a way to approach the problem. Your question is too broad to give an exact simple answer but I do understand why are you asking such question.
You can use Osmdroid library to display the route you have on Android.
Keep in mind that the core feature of Osmdroid is to display the map tiles. Map tiles are just bitmaps so you need either an online source of tiles or an offline one. How to do that is covered in the documentation and partly in other questions on SO. It's a too big topic to explain it here in detail. Just to make it clear: .osm file with raw OpenstreetMap data cannot be directly rendered by Osmdroid. Map tiles are usually rendered from that data in quite complex way and not on the fly.
Another very important feature in Osmdroid library is the ability to display so called Overlays. E.g. Markers, polygons etc. You may use those to draw your route on the map and other features you may wish to display. This is again covered in the documentation and too big to go in details here.
There is a support for routing for Osmdroid (AFAIK in Osmbonuspack) but that's about using some 3rd party service to get your routing data and displaying that. According to your comment you want to implement your own algorithm and therefore this would be no use to you.
So the last part is how to integrate your algorithm into that. That's not a simple question with a simple answer. You'll need to do almost everything on your own, starting with getting the data you need to run the algorithm from the OpenstreetMap database (.osm file). I don't think there's an API which would provide you reasonable way to access the data in a form suitable for route computation. The approach I would choose is to develop some kind of preprocessing which would take either .osm file or a database with the data an produce my own structure representing the graph for navigation. I would than include this graph in my application and run my algorithm on that data. The output of my algorithm would be the route: a list of coordinates which I would use to draw the polyline.
If the area you need to cover is small enough, you may start with including the .osm file in your project and running the algorithm in the same was as you do now. Maybe it's going to be good enough for your situation.
One interesting project to look at to find inspiration is Graphopper - they have build exactly what I said above and they use it to provide a library for Android/iOs and a web API. But the core is the same - pre-process OSM data into graph data and run the algorithm on that. Since you wish to implement the algorithm on your own this library will not help you (unless you fork the project and modify it) but it might be a valuable learning resource.
I want to make my final year project and for my idea I'd need the 3d buildings from google maps extracted somehow. Does google maps support this? Is it achievable ? I couldn't find anything really relevant on the internet.
I think the reason why you didn't find anything related to Google Maps is that the 3D information belongs to Google Earth. Google Maps/Earth API doesn't support this directly as far as I know.
The link below describes a process to get the information, I didn't test it and it's too complex and not mine to repeat here but basically "the only way to obtain this geometry is to capture it from the systems graphics engines (directX or opengl)." :
http://zachsoflin.com/blog/2012/03/01/extract-geometry-from-google-earth-to-mesh/
If you google "Extracting 3d models from google Earth" you'll get more results.
I'm not sure if this will work, but have you tried 3D information from OpenStreetMap? I think some like http://www.osm-3d.org/map.htm have building height layers available, if that's what you're looking for.
Here you can find a tutorial for extracting the 3D models from Google Earth.
I need a Map API for Android that can provide me with indexed nodes and indices that make up the road network. The main idea is to determine if two GPS devices are on the same road. Thank you in advance
A Map API by itself will not have that information. Anyway, you can get it from OpenStreetMap freely. You can download it from here.
I don't understand from your question if you intend on displaying the results on a map. If so, and you want a nice and free map API, I would suggest Leaflet. It's not as mature as the likes of OpenLayers but, as you've tagged this post with "android", Leaflet just kicks ass in the mobile department.
OpenStreetMap is definitely a good source of data for this kind of project. Unlike google maps, it gives developers access to the underlying vector data of a map (fully open). This allows interesting new use cases which simply are not possible with google maps, and something involving geometric calculations like this would definitely fit into that category. You either need OpenStreetMap or some other source of "vector" map data, and beyond OpenStreetMap this can be expensive.
Unfortunately that's not the full answer to your question. You still have a lot of work to do to use the data in the way you intend. You need to calculate the proximity of two points (GPS readings from two devices?) to nearby roads, and figure out which road the point lies closest to. It's the kind of powerful geo calculation you might do using a GIS package such as QGIS or a functions of a geo-aware database system PostGIS.
But that's not the answer to your question, because you need to do these calculations on device. I'm not aware of an off-the-shelf library to do this on android. I think you would have to roll your own.
But another challenge is to get the vector data onto the device in a suitable format in the first place, and this is the first thing to solve. You'd want the vector data either as a large download for a whole country, or perhaps a smaller area, perhaps with an on-the-fly download feature within this app. Whole countries are not infeasible when working with maps in vector form (ever tried the awesome MayDroyd app?), but require some compact formatting. Happily some of these problems are starting to be solved in open source off-the-shelf libraries. You could try to build on top of MapsForge for example.
So then you're back to the challenge of writing on-device code to poke around in this data and do the calculations you want to do. I suppose it could be rather good if projects like MapsForge included generic PostGIS style geo-functions to make this easier. Something to ask the mapsforge developers about perhaps.
I am trying to build an android application that allows user to login through signing on a canvas, I can't find any algorithm that will help me implement this functionality in reliable manner , I read alot of papers and methods about signature recognition such as fourier transform method but all the papers involve very complex mathematical operations which makes it very hard to implement using the android sdk.
so is there any open source algorithm that would compare two signature bitmaps(drawables) to obtain descent results?
if not how should I go about this issue?
Comparing drawables may be not sufficient, as signatures may differ in size and position. You can attempt recognition based on invariant moments ( I use this technology for OCR,
but on printed characters, see demos in http://sourceforge.net/projects/javaocr/ project )
You may get better results analysing signature process in dynamics - path, speed, energy etc.
I don't know anything about it but I feel there is sample app installed in the emulator called GestureBuilder which can help you. You can refer Gesture for this.
I am writing an Android-application that is supposed to download a bunch of addresses from my SQL-server, reverse geocode them, compare them all to my current location and return the one that is closest to me, not geometrically, but the one that I am the shortest driving distance from.
I have managed to get the reversed geocoding to work, but when I run my program a few times, I hit the OVER_QUERY_LIMIT on google. Needless to say, there are quite a few addresses in my database.
I understand that I could do this the quick and dirty way and just see which address is nearest to me by comparing the latitude and longitude of my current position and that of my addresses as opposed to comparing it to the actual driving distance. The problem with this is that this application will be used in a region where there are quite a lot of lakes to drive around and using that method will likely return quite a few stupid results.
How can I keep this from happening over and over? Can I present google with a view of all my addresses and just do a comparison once? I really need help with this one.
Actually, you will have to query a routing service (not necessarily Google Maps, to my knowledge also Cloudmade provides you with routing; there definitely are more) to get driving directions to each of the Points Of Interest around you and then select the closest one. This is a very bad practice, as you are very limited with the request amount.
According to the Google Maps API TOS (paragraph 10.1.3) you are not always allowed to do that.
What I did in a similar case was to store the coordinates for all POI, and look up the closest ones just by range of lat/lng.