Google Maps has the function isLocationOnEdge(point, polyline, tolerance) that takes a tolerance value in degrees and uses it to determine whether a point falls near a polyline.
Is there anything similar in Leaflet(or some plug-in) that does the same thing?
A handful library for such operation is Turf.
For your case, a simple approach would be to:
Create a polygon out of your polyline using turf.buffer with appropriate "tolerance" (Turf takes a distance at Earth surface, or degrees).
Check whether your point is within that polygon or not using turf.inside.
Unfortunately, turf.buffer is only an approximation, it does not takes geodesy into account… therefore for big tolerance you will have a deformed shape.
An exact method could be to:
Use instead turf.pointOnLine to find the nearest point of the polyline.
turf.distance to measure the distance between those 2 points, and compare with your tolerance (or even just Leaflet latLng.distanceTo, but you would have to convert GeoJSON points back to Leaflet LatLngs).
Related
I was wondering how I can go about storing and displaying small, but geographically accurate distances in the mapbox unity SDK?
I'm storing radius' about markers on a map, I get the value in meters (from ~0.5m-10m), and then, adaptively with the zoom level, I want to accurately display those meters in Unity world space (draw an ellipse) using these stored values. The problem is that the mapbox api from my understanding only lets you to convert lat/long to unity world coordinates and I'm running into precision errors. I can get adequate precision when using the CheapRuler class and meters, but as soon as I use the _map.GeoToWorld(latlon) method the precision is lost.
How would I go about keeping adequate precession, is there a way I can use the marker as the reference point and the radius as the offset, and get the relative unity world coordinate distance (of the radius) that way? I know you can also store scale relative to the mapbox tiles, but I'm not sure how I can convert that back to a unity world distance. I'm operating on very small distances, so any warping due to lat/long being a Mercator projection can probably be ignored.
I figured out a round-about solution.
First I convert the meters into unity world space using whatever IMapScalingStrategy Mapbox is currently using.
Then I convert from world to the view space of whatever camera I want to scale to the given bounds.
After that, I use find out the scale of the bounds, solving for:
UnityRelativeScaleChange = 2Map Zoom Level Change; which (to my estimations) is the relationship between unity scale and mapbox zoom levels.
This solutions works great as long as you don't have to zoom in/out by too much, otherwise you'll run into precision problems as the functions rely on the relative view-based size of a given bounds to do their calculations which will lead to unstable results if those initially take a tiny portion of the screen.
I am using mapbox-gl and have point and line layers on the map. All layers are vector tiles. Some points lie on the lines, some not and I want to hide points that don't lie on the lines
Is it possible to do it only on the frontend side with writing something like a filter that checks if a point on any line or not? I really don't want to change the backend
Why don't you use turf.js in conjunction with mapbox-gl-js?
E.g. you could calculate the distance to the line with http://turfjs.org/docs/#pointToLineDistance for each point, then filter out any points with a distance bigger than 0.
I have a game map that has been tiled over the world map of MapKit. I generate a path to take for the player. With this I find the 3 nearest nodes (in game cities) and select one at random then recurs this to find a 3rd node. I have some logic that means the chosen nodes at each stage aren't in any of the previous arrays to allow for a nice path and no "coming back on your self".
However, the issue I'm facing is I'm using CLLocation.distance(), this unfortunately uses an euclidean distance calculation due to the curvature of the earth. Is there any way to off set the curve as my current logic ends up in all paths slowly leaning towards the poles as the world map is just a flat image.
I've thought about translating CLLocation to a UIView between the first node and all possible second nodes, however this becomes massively intensive.
Any ideas on how to either offset the curve calulation or remove it all together?
I am storing a number of point features inside a SQLite database for display inside of MKMapView and I would like to precompute and store coordinates in the the projection of the map instead of in lat/lon (for index/performance reasons). However, I am creating this database externally (in Python), so I cannot simply use the MKMapPointForCoordinate() function. What is the projection used by MKMapView? The documentation states that it is a mercator projection but it does not appear to be the web mercator projection that I expected. How can I compute an X/Y coordinate from a Lat/Lon ?
Personally I feel you're approaching the problem from the wrong angle - you say don't want to store latitude/longitude co-ordinates for 'index/performance reasons'. What are these reasons?
Storage, indexing, and querying of geographic coordinates inside of a database is not an unusual problem. They are simply two decimal numbers, making indexing and querying very straightforward.
Apple also tell you only to save co-ordinates rather than MKMapPoints in their own documentation:
When saving map-related data to a file, you should always save coordinate values (latitude and longitude) and not map points.
Perhaps you could share some of the issues you're having saving co-ordinates to a database?
I'm pretty sure it is webmercator because the overlay tiles I have produced are in that projection and they fit. But like other conmenters said, you're advised to store them in lat/long. If you want to query results in a grid lat/long provide a pretty good starting point. The grid isn't square as you leave the equator but it is rectangular.
I have a series of nature reserves that need to be plotted, as polygon overlays, on a map using the coordinates contained within KML data. I’ve found a tutorial on the Apple website for displaying KML overlays on map instances.
The problem is that the reserves vary in size greatly - from a small pond right up to several hundred kilometers in size. As a result I can’t use the coordinates of the center point to find the nearest reserves. Instead I need to calculate the nearest point of the reserves polygon to find the nearest one. With the data in KML - how would I go about trying to achieve this?
I've only managed to find one other person ask this and no one had replied :(
Well, there are a couple different solutions depending on your needs. The higher the accuracy required, the more work required. I like Phil's meanRadius parameter idea. That would give you a rough idea of which polygon is closest and would be pretty easy to calculate. This idea works best if the polygons are "circlish". If the polygon are very irregular in shape, this idea loses it's accuracy.
From a math standpoint, here is what you want to do. Loop through all points of all polygons. Calculate the distance from those points to your current coordinate. Then just keep track of which one is closest. There is one final wrinkle. Imagine a two points making a line segment that is very long. You are located one meter away from the midpoint of the line. Well, the distance to these two points is very large, while, in fact you are very close to the polygon. You will need to calculate the distance from your coordinate to every possible line segment which you can do in a variety of manners which are outlined here:
http://www.worsleyschool.net/science/files/linepoint/distance.html
Finally, you need to ask yourself, am I in any polygons? If you're 10 meters away from a point on a polygon, but are, in fact, inside the polygon, obviously, you need to consider that. The best way to do that is to use a ray casting algorithm:
http://en.wikipedia.org/wiki/Point_in_polygon#Ray_casting_algorithm