View Dror Gluska's profile
I had an idea for a geographic application not so long ago and I was looking for an algorithm to find all elements in a specific region (e.g. spatial index), finally I came upon an algorithm called RTree but I still couldn't find a C# code.
So I decided to port Java Spatial Index Library
You can find it here:
https://sourceforge.net/projects/cspatialindexrt/
Basic usage
Create a new instance:
RTree.RTree<T> tree = new RTree.RTree<T>();
Create a rectangle:
RTree.Rectangle rect = new RTree.Rectangle(1, 2, 3, 4, 5, 6);
Add a new rectangle to the RTree:
tree.Add(rect, object);
Check which objects are inside the rectangle:
var objects = tree.Contains(rect);
Count how many items in the RTree:
var i = tree.Count;
Check which objects intersect with the rectangle:
var objects = tree.Intersects(rect);
Create a point:
RTree.Point point = new RTree.Point(1, 2, 3);
Get a list of rectangles close to the point with maximum distance:
var objects = tree.Nearest(point, 10);
The library's code can be improved, but I needed something quick for a POC.
So I decided to port Java Spatial Index Library
You can find it here:
https://sourceforge.net/projects/cspatialindexrt/
Basic usage
Create a new instance:
RTree.RTree<T> tree = new RTree.RTree<T>();
Create a rectangle:
RTree.Rectangle rect = new RTree.Rectangle(1, 2, 3, 4, 5, 6);
Add a new rectangle to the RTree:
tree.Add(rect, object);
Check which objects are inside the rectangle:
var objects = tree.Contains(rect);
Count how many items in the RTree:
var i = tree.Count;
Check which objects intersect with the rectangle:
var objects = tree.Intersects(rect);
Create a point:
RTree.Point point = new RTree.Point(1, 2, 3);
Get a list of rectangles close to the point with maximum distance:
var objects = tree.Nearest(point, 10);
The library's code can be improved, but I needed something quick for a POC.
Hi,
ReplyDeleteI do a test. I have 2 geo points. I use the Microsoft.SqlServer.Types.dll to calc the distance between 2 points.
the result is 934.888984856364 meters.
I use your RTree nearest method. it returns the 123 values. I set the furthestDistance parameter to 0.03F.
So I think the returned result is wrong.
Do you have any idea?
var lat=31.240426F, long=121.482235F;
var Bund1 = SqlGeography.Point(lat, long, 4326); //Bund Riverside
var Bund2 = SqlGeography.Point(31.232014, 121.481559, 4326); //Bund (Superior)
Console.WriteLine(Bund1.STDistance(Bund2)); // distance is 934.888984856364 meters
var tre = new RTree.RTree();
tre.Add(new RTree.Rectangle(31.232014F, 121.481559F, 31.232014F, 121.481559F, 0.0F, 0.0F), 123);
var li = tre.Nearest(new RTree.Point(lat, long, 0.0F), 0.03F);
I think you're confusing spatial and geographical.
DeleteRTree is a spatial index while SqlGeography is geographical.
Calculating distance between two points in 2D space:
http://www.mathwarehouse.com/algebra/distance_formula/index.php
Calculating distance between two geographical points is a bit more complicated:
http://www.movable-type.co.uk/scripts/latlong.html
The numbers you provided are lon/lat, which means they are the angles from the equator/Greenwich on Earth, the distance uses the earth radius to calculate distances.
Oh....,, Thank you SO MUCH!!!!
DeleteHi Denis,
ReplyDeleteYou should instantiate RTree with your container type instead of object, create a class and store all the properties you'd like to associate with a particular point/rectangle.
I'll need a specific example to be more specific :-)
Hi, just a quick one really, can the RTree.RTree and all of its added instances be serialized, written out into a binary stream and retrieve it from them later on?
ReplyDeleteHi, the Nearest function seems to have a bug when used in multi-threaded environment. It is because nearestIds is global, so simultaneous invocation of the same rtree object Nearest function will cause an exception because it is trying to modify the list while some other process is iterating through that same list.
ReplyDeleteThanks!
Didn't know the library was still in use, its pretty old...
DeleteI've migrated it to github: https://github.com/drorgl/cspatialindexrt
I did a quick fix, feel free to test it or do a pull request.