It seems to be a known fact that MKMapView (and Google's maps in general) have a varying offset on 100-600m which makes annotations display incorrectly on the map.
According to this thread, Google has a private method called _applyChinaLocationShift, and it works, but apparently only for CLLocations that are given by CLLocationManager. For arbitrary CLLocations, it returns nil. The app I'm writing only needs to work in one city, so I've thought of pre-sampling the area using _applyChinaLocationShift and store the inverse transforms in the shipped app if that was possible.
So basically, is there any way to convert a coordinate to a coordinate that corresponds to the transformed China maps?
How about using location simulation in the Simulator and feeding it a bunch of coordinates in that particular city.
Related
I can't find any documentation about using mile markers, only latitude and longitude. Is this even possible? Basically the situation is I get a JSON with a road and a mile marker and I want to be able to represent that data on a map. I know I could tediously convert mile markers to coordinates, but that just seems asinine. Is there another way?
You will likely need outside data for this. Check state or even US DOT data sources for something you could use here. You could then represent it on a map with MapKit directly (annotations) or possibly look into making your own raster layer with Mapbox Studio.
I am trying to find a way to create several polygon geofences with iOS. I need to draw multiple zones in a city to represent areas, streets, etc. From what I've read so far, iOS only allows circular zone from a geolocated device.
Is it feasible with iOS?
Is there a web app somewhere to draw polygons on a map and generate the coordinates in an array?
1) iOS only allows to create circular geofences indeed however what you are trying to achieve is possible with some extra logic.
I have developed similar features so I suggest you to do the following:
create a circular geofence that embeds your polygon
when the device gets notified as being within the circular geofence,
start the GPS
every time you get a location update, check if its coordinates are
within the polygon
turn off the GPS as soon as the device's location is found within the
polygon, unless you need to be notified when exiting the polygon as
well
turn off the GPS when the device gets notified as outside the
circular geofence
As you need polygon geofences I guess you expect a good level of accuracy, so you would need to use an extra layer of GPS on top of the geofencing anyways, as geofencing is not accurate at all.
2) Have a look at those links:
https://github.com/thedilab/v3-polygon-shape-creator
https://github.com/tparkin/Google-Maps-Point-in-Polygon
I'm working on an app that lets a user select locations on a map. The entire map is subdivided into irregular regions (administrative boundaries), and when a user touches a point on a map, I need to be able to figure out which region the point belongs to. Just to clarify, there is no finite set of points for a user to choose from, they just tap anywhere on the map.
What is the best way to achieve this? I have been looking at MKPolygon class but cannot really figure out if this is the way to go. If it is, would I be using intersectsMapRect: method of the MKOverlay protocol to check for a match? Are there any good tutorials on this kind of map operations?
A good approach here might be the MapBox iOS SDK and it's RMInteractiveSource, which is designed for this. Check out this sample app which shows interactive regions.
This is done by a space-optimized, offline-capable key-value store of sorts that keys pixels at varying zoom levels to arbitrary content values (region name, data, imagery, etc.)
In MapKit proper, you'll need some sort of spatial analysis (maybe Spatialite?) to determine intersections between points touched and irregularly-shaped regions.
I see some ways to do it:
1) Draw using OpenGL programmatically.
2) Draw using QuartzCore and CoreAnimation programmatically.
3) Draw map in AutoCad and then somehow connect it to iOS.
4) Draw map using SVG.
Requirments are supporting pathfinding and gps navigation.
For first 2 ways I think that it's expensive in terms of performance way, redraw all elements on scaling; and I don't think that this way may have GPS-navigation support.
Using AutoCad pictured maps is hard to understand for me how to connect it with graphs\paths for pathfinding.
My colleagues will develop this app on web using SVG. I found it - https://github.com/SVGKit/SVGKit , but still have no idea how it will support pathfinding and navigation.
I would appreciate any help.
Generally there are two types of map application:
A) They display a map, (with or without a user position) without needing to calculate a path like a navigation system does (see point B)
B) Application that use the vectors of a map and calculate something: e.g to find a best path. The shortest connection, e.g A navighation system , etc.
Application for A) are usually less complex then that of B), because the vectors can be somewhat inacurate, have no conections, have small gaps, have no logic between the edges, etc.
1) To only display a building map, you would only need a list of edges. (An edge is pair of coordinates (x1,y1) - (x2,y2). How ever you get that. E.g MapInfo Professional format mif/mid.
Or even you could dispaly a pdf that contains the map of the builing. Right with the built in PDF View, (also with SVG but more difficult).
Things get much more complicated if it is not a relative map, but also a map that is positioned with an reference coordinate system, like latitude/longitude (WGS84).
In that case you would use a Tool (mapInfoProfessional, to import AutoCad DXF Files, and apply 3 GPS measured reference points at the corner of the house, and convert that to LatLong WGS84 coordinates system.
With ios you cannot measure that 3 Points because you cannot average a position, ios stops sending when you are standing still at one corner of the house.
You could try to extract the positions from a google earth satellite foto if you are living in a region where google Sattelite fotos have high resolution. (But this might violate the license conditions of that Satellite Foto provider (Topic: derived data))
Finally you now have a list of edges in Lat Lon coordinate System.
For Displaying I personally would either do with 1) OpenGL) or 2) Quartz2D.
Now the Path finding part.
Probaly you need a second "map" that defines the possible paths inside the building.
This structure must be a connect graph (points with connected neighbours).
Computer games do it that way. (Some even allow you to display that path in developper mode)
The path can be drawn, in a different layer of the floor plan. But this path
has higher requirements: No gaps are allowed, all must be perfect connected.
Call that layer "Path" and export it as own plan.
Now use only this path layer, and import, and create a graph of nodes with connect neighbours.
Use Dijkstra Algo to search for shortest path.
I made a very simple APP in which I can throw a pin right onto the location I am standing at (just a beginner's practice). But I found a problem.
I swear neither I was moving nor the device thought I was moving. And I directly use the geolocation to set the pin. but the pin and the current-location blue point are hundreds of meters apart.
(By the way, the blue point expressed my real location at the time.)
This is a famous problem of Google Map on iOS in China. Put aside the complicated issue of the so-called national security, where I want help is what should we do as a developer. Technically, is there a way, in programming, to figure out what exactly the offset is and correct it?
Does anyone have any idea?
At what time did you place the pin? iOS has up to three sources of location data (cell tower triangulation, Wifi sniffing and GPS) and will keep you up to date with the most accurate. So often you get a not very accurate location, then a more accurate location, then an even more accurate location.
If you have a MKMapView open then something you can do is key-value observe on its userLocation property rather than starting any sort of CLLocationManager. That way you'll always be updated with whatever the map view has decided is the current location, meaning that you don't need to try to match your logic to its.
I did some research on the offset, but haven't gotten a satisfying result yet. The added offset is deterministic, i.e. given a location, the deviated location is fixed. So my goal is to get the deviation function, f(p)=p', where both p and p' are 2D points. You can check here if you are interested.