I'm trying to find an algorithmic way to select which points fall within a specific arbitrarily shaped area on a Google Map. Basically I want to be able to provide a point and ask a function if that point lies within an arbitrary (but specifically defined) map area.
For example, how could I tell if a point was contained within the green section (Brions Regional Park) on the follow map:
http://maps.google.com/maps?ie=UTF8&q=state+park&fb=1&gl=us&ei=Rm-tTIGRBI2jnQeXrZyTBg&ved=0CEoQtgMwAw&sll=37.912242,-122.078705&sspn=0.086,0.17355&split=1&rq=1&ev=zi&radius=5.68&hq=state+park&hnear=&ll=37.934585,-122.13192&spn=0.089358,0.17355&z=13
I need help figuring out how to define the specific area and also then the algorithm that would take in the defined area & point and return true/false.
Thanks in advance for your help!
This has been helpful for me:
https://github.com/tparkin/Google-Maps-Point-in-Polygon
Related
I want to the count of markers based on location using leaflet map
ie,
Say in india
Number of markers in bangalore
number of makers in mysore so on...
only thing i would think of to do this is using contains( point )
which is in the doc
But how to use it to find the maker is in that region as i will not be aware of the coordinates of the region
Is there a way to check like
region.contains(markerLatLang)
Leaflet .contains() works on L.LatLngBounds objects, which are actually a rectangular region. So it tells if your point / marker is within a rectangle or not.
You would need first to retrieve yourself the coordinates of your administrative areas of interest (India, etc.). See https://gis.stackexchange.com/questions/199765/where-to-get-world-wide-detailed-administrative-boundaries
BTW, a simple version of countries boundaries can be: https://github.com/johan/world.geo.json
Then you would probably want to use a more accurate detection method, for example leaflet-pip plugin or turf.js, which will actually check if your point is within arbitrarily shaped polygons, not just a rectangle.
See for instance Leaflet event: how to propagate to overlapping layers
I am trying to do a grid based clustering, specifically where each U.S. state is a grid. What I am doing now is just setting strategy option of ClusterProvider to STRATEGY_GRID_BASED, but I don't think this is what I think it is.
I tried looking into nokia.maps.clustering.IGridOptions, but there isn't anything documentation on that.
Can someone point me in the right direction? Thanks.
A Grid-based clustering strategy just breaks the map up into squares and calculates how many markers are found in each square. What you are after is known as a Chloropleth Map. The most efficient way to do this would be to cluster server-side, return a key,value pair (i.e. state, number of markers) and just display polygons for the US States. An example of such a map can be found in the HERE Maps community examples which displays the accession dates of states to the union.
If you insist on doing everything client side then you'd have to use the following pseudo code instead:
Iterate though each marker in your list:
Check to see if it is within the hit area of an existing polygon.
If it is - increment the markers counter (an additional attribute you have added.)
If it isn't make a WKT State-level shape geocoding request, and parse the result -add a new markers counter attribute to the Polygon
repeat
You will then end up with a series of polygon objects each holding an attribute with the number of markers within found within the state.
Ok, here is the thing. Recently i decided i wanted to understand how Random map generation works. I found some papers and some arguments. The most interesting one was "Diamond Square algorithm" and "Midpoint Displacement". I still have to try to apply those to a software, but other than that, i ran into this site: http://www-cs-students.stanford.edu/~amitp/game-programming/polygon-map-generation/
As you can see, the idea is to use polygons. But i have no idea how to apply that a Tile-Based map, not even how to create those polygons using the tools i have (c++ and sdl). I am assuming there is no way to do it ( please correct me if i am wrong.) But if i am not, how does a non-tile map works, and how are these polygons generated?
This answer will not give you directly the answers you're looking for, but hopefully will get you close enough!
The Problem
I think what blocks you is how to represent the data. You're probably used to a 2D grid that simply represent the type of each tile. As you know, this is fine to handle a tile-based map, but doesn't properly allow you to model worlds where tiles are of a different shape.
Graphs
What I suggest to you, is to see the problem a bit differently. A grid is nothing more than a graph (more info) with nodes that have 4 (or 8 if you allow diagonals) implicit neighbor nodes. So first, what I would do if I was you, would be to move from your strict standard 2D grid to a more "loose" graph, where each node has a position, a position, a list of neighbors (in most cases you'll have corners with 2 neighbors, borders with 3 and "middle" tiles with 4) and finally a rendering component which simply draws your tile on screen at the given position. Once this is done, you should be able to have the exact same results on screen that you currently have with your "2D Tile-Based" engine by simply calling the rendering component with each node who's bounding box (didn't touch it in what you should add to your node, but I'll get back to this later) intersects with the camera's frustum (in a 2D world, it would most likely if the position +/- the size intersects the RECT currently being drawn).
Search
The more generic approach will also help you doing stuff like pathfinding with generic algorithms that explore nodes until they find a valid path (see A* or Dijkstra). Even if you decided to stick to a good old 2D Tile Map game, these techniques would still be useful!
Yeah but I want Polygons
I hear you! So, if you want polygons, basically all you need to do, is add to your nodes a list of vertices and the appropriate data that you might need to render your polygons (either vertex color, textures and U/V maps, etc...) and update your rendering component to do the appropriate OpenGL (this for example should help) calls to draw your nodes. Once again, the first step to iteratively upgrade your 2D Tile Engine to a polygon map engine would be to, for each tile in your map, give each of your nodes two triangles, a texture resource (the tile), and U/V mappings (0,0 - 0,1 - 1,0 and 1,1). Once again, when this step is done, you should have a "generic" polygon based tile map engine. The creation of most of this data can be created procedurally by calculating coordinates based on tile position, tile size, etc...
Convex Polygons
If you decide that you ever might need NPCs to navigate on your map or want to allow your player to navigate by clicking the map, I would suggest that you always use convex polygons (the triangle being the simplest for of a convex polygon). This allows your code that assume that two different positions on the same polygon can be navigated to in straight line.
Complex Maps
Based on the link you provided, you want to have rather complex maps. In this case, the author used Voronoi Diagrams to generate the polygons of the map. There are already solutions to do triangulation like that, but you might also want to use other techniques that are easier to work with if you're just switching to 3D like this one for example. Once you have interesting results, you should consider implementing serialization to save/open your map data from the game. If you want to create an editor, be aware that it might be a lot of work but can be worth it if you want people to help you creating maps or to add elements to the maps (like geometry that's not part of the terrain).
I went all over the place with this answer, but hopefully it helps!
Just iterate over all the tiles, and do a hit-test from the centre of the tile to the polys. Turn the type of the tile into the type of the polygon. Did you need more than that?
EDIT: Sorry, I realize that probably isn't helpful. Playing with procedural algorithms can be fun and profitable. Start with a loop that iterates over all tiles and chooses randomly whether or not the tile is occupied. Then, iterate over them again and choose whether it is occupied or its neighbour is.
Also, check out the source code for this: http://dustinfreeman.org/toys/wall7-dustin.html
I have been looking at posts about determining if a point lies within a polygon or not and the answers are either too vague, abstract, or complex for me. So I am going to try to ask my question specific to what I need to do.
I have a set of points that describe a non-straight line (sometimes a closed polygon). I have a rectangular "view" region. I need to determine as efficiently as possible whether any of the line segments (or polygon borders) pass through the view region.
I can't simply test each point to see if it lies within the view region. It is possible for a segment to pass through the region without any point actually inside the region (ie the line is drawn across the region).
Here is an example of what I want to determine (red means the function should return true for the set of points, blue means it should return false, example uses straight lines and rectangles because I am not an artist).
Another condition I want to be able to account for (though the method/function may be a separate one), is to determine not just whether a polygon's border passes through the rectangular region, but whether the region is entirely encompassed by the polygon. The nuance here is that in the situation first described above, if I am only concerned with drawing borders, the method should return false. But in the situation described here, if I need to fill the polygon region then I need the function to return true. I currently do not need to worry about testing "donut" shaped polygons (thank God!).
Here is an example illustrating the nuance (the red rectangle does not have a single vertex or border segment passing through the on-screen region, but it should still be considered on-screen):
For the "does any line segment or polygon border pass through or lie on screen?" problem I know I can come up with a solution (albeit perhaps not an efficient one). Even though it is more verbose, the conditions are clear to me. But the second "is polygon region on screen?" problem is a little harder. I'm hoping someone might have a good suggestion for doing this. And if one solution is easily implemented on top of the other, well, booya.
As always, thank you in advance for any help or suggestions.
PS I have a function for determining line intersection, but it seems like overkill to use it to compare each segment to each side of the on-screen region because the on-screen region is ALWAYS a plain [0, 0, width, height] rectangle. Isn't there some kind of short-cut?
What you are searching for is named a Collision Detection Algorithm A Google search will lead you to plenty of implementations in various language as well as a lot of theory
There are plenty of Geometric theory behind, from the simplest bisector calculus to Constrained Delaunay Triangulations and Voronoi Diagrams (that are just examples). It depends on the shape of Object, the number of dimensions and for sure the ratio between exactness needed and computing time afforded ;-)
Good read
PS I have a function for determining
line intersection, but it seems like
overkill to use it to compare each
segment to each side of the on-screen
region because the on-screen region is
ALWAYS a plain [0, 0, width, height]
rectangle. Isn't there some kind of
short-cut?
It's not an overkill, its neccessary here. The only kind of shortcut I can think of is to hardcode values [0, 0, width, height] into that function and simplify it a bit.
A question from a novice. Is it possible to design a tool to select color range and create a vector map within that given range to integrate into a flash tool? basically a feature that mimics the wand tool effect in photoshop, but creating a vector outline of the range selected. Any reading material to help with this would be greatly appreciated.
I think you are looking for either 2D segmentation, if you want all the selected colors in the image to be selected, or flood fill if you want to find the region surrounding some initial point where all the colors are in the desired range.
When you say vector map, I imagine you mean the outline of the pixels to select. In which case it's probably easier to find the pixels you want and then draw round then rather than explicitly creating a polygon to contain them.