If I have two shapes displayed on Bing-Maps can I do any set Math?
What I really want is to take two intersecting shapes, determine a 3rd shape for the intersection and then reduce the the original shapes to exclude the intersection.
I actually have the intersection shape so the key bit is taking a 'bite' out of the original shapes.
Reason for doing this is currently displaying the intersection as a third layer (to give a specific colour) produces a largely occluded map, what with part of the transparent shape1 and shape2 and the intersection all covering the same bit of the map.
If I could 'cut-down' the two main shapes only the intersection shape would colour/cover that part of the map.
I do not think there are out of the box solutions in the Bing Maps API. I have done something similar in the past with Bing Maps API and SqlGeography Class though. Its easy to loop through the points of our Bing Polygons, therefore we can plot them into SqlGeography Polygons or SqlGeometry Polygons.
You will need the Microsoft.SqlServer.Types.dll to make use of this class, but it is free with SqlExpress.(Note that you do not actually need SQL Server installed, you just need to reference the DLL)
You can use the SqlGeography Class (or SqlGeometry Class) to find intersecting shapes and points. Perhaps have a look at STIntersection Method, According to MSDN STIntersection will;
"Returns an object representing the points where a SqlGeography instance intersects another SqlGeography instance."
Once you have the object representing the shape were a SqlGeography instance intersects another, you know you need to somehow adjust any points from the compaired instances that lie withing the SqlGeography instnace returned by StIntersection.
Here is a simular question where Peter uses STDifference. To subtract the two shapes.
I'll provide you with a c# example I made quickly for the Intersection. I had a lot of trouble finding any code examples for anything that wasn't purely SQL Server based.
SqlGeography Shape1 = new SqlGeography();
SqlGeographyBuilder geographyBuilder1 = new SqlGeographyBuilder();
geographyBuilder1.SetSrid(4326);
geographyBuilder1.BeginGeography(OpenGisGeographyType.Polygon);
geographyBuilder1.BeginFigure(47.4275329011347, -86.8136038458706);
geographyBuilder1.AddLine(36.5102408627967, -86.9680936860962);
geographyBuilder1.AddLine(37.4928909385966, -80.2884061860962);
geographyBuilder1.AddLine(38.7375329179818, -75.7180936860962);
geographyBuilder1.AddLine(48.0932596736361, -83.7161405610962);
geographyBuilder1.AddLine(47.4275329011347, -86.8136038458706);// Remember last point in the polygon should match the first
geographyBuilder1.EndFigure();
geographyBuilder1.EndGeography();
Shape1 = geographyBuilder1.ConstructedGeography;
SqlGeography Shape2 = new SqlGeography();
SqlGeographyBuilder geographyBuilder2 = new SqlGeographyBuilder();
geographyBuilder2.SetSrid(4326);
geographyBuilder2.BeginGeography(OpenGisGeographyType.Polygon);
geographyBuilder2.BeginFigure(47.4275329011347, -86.8136038458706);
geographyBuilder2.AddLine(36.5102408627967, -86.9680936860962);
geographyBuilder2.AddLine(37.4928909385966, -80.2884061860962);
geographyBuilder2.AddLine(47.4275329011347, -86.8136038458706);
geographyBuilder2.EndFigure();
geographyBuilder2.EndGeography();
Shape2 = geographyBuilder2.ConstructedGeography;
SqlGeography IntersectedShape = Shape1.STIntersection(Shape2);
I believe you can draw shapes with the new GeoRSS feature - it supports line, boxes, polygons and circles. GeoRSS was designed as a lightweight, community driven way to extend existing feeds with geographic information. Also check out GeoJson
Related
Is it possible to dim or hide the "rest of the world" except one country on a standard leaflet.js map? Mabye overlay out with some kind of "inverted polygon" with the contours of the country? Any code examples or links would be appreciated.
Expanding #tmcw's answer ...
The secret is to draw a polygon using the property described in http://leafletjs.com/reference.html#polygon
You can also create a polygon with holes by passing an array of arrays
of latlngs, with the first latlngs array representing the exterior
ring while the remaining represent the holes inside.
The first polygon will be a rectangle as big as the map itself, the hole will be the country you want to highlight.
L.polygon( [outerBoundsLatLngs, latLngs] );
Here is a working example: http://jsfiddle.net/FranceImage/1yaqtx9u/
See the leaflet-maskcanvas and L.Mask plugins
I have a collection that has a 2d geospatial index on a field (center) which is an array of long/lat, the collection also has a radius field. So each item can represent a circle. I know that mongodb has a operator $within, and I want to get a list of all items that contain a specific point [long,lat], but it seems that I can only check which points are within a specific shape.
You are correct, right now, you can't do what you want. Please file a feature request at http://jira.mongodb.org as I can't find one already existing for this.
This is how I solved it (i.e. get a shape that covers a given point) in my situation, using a basic grid. It has a limited accuracy, depending on the grid resolution:
create a collection "grid" with points that covers the common bounding box of all your shapes (use a nested for loop in javascript)
create a 2d index on the grid
for each shape, search for all the grid points that lie within the shape; label each grid point with the id of the shape (use an array attribute on the grid point)
To see in what shape(s) a point lies, search for the closest grid point, and return its assigned shape(s) property. First check for the common bounding box, because points outside it should always return 'not in any shape', and not use the closest grid point.
Depending on the precision you need, this might or might not be a usable solution. The accuracy depends on how many points you put in your grid, and you may be able to do something smart with local densities of your grid.
I am able to draw shapes using the UIBezierPath object. Now I want to identify different shapes drawn using this eg. Rectangle , Square , Triangle , Circle etc. Then next thing I want to do is that user should be able to select a particular shape and should be able to move the whole shape to different location on the screen. The actual requirement is even more complex , but If I could make this much then I can work out on the rest.
Any suggestion or links or points on how do I start with this is welcome . I am thinking of writing a separate view to handle every shape but not getting how do I do that..
Thank You all in advance !!
I recommend David Gelphman’s Programming with Quartz.
In his chapter “Drawing with Paths” he has a section on “Path Construction Primitives” which provides a crossroads:
If you use CGContextAddLineToPoint your user could make straight lines defined by known Cartesian points. You would use basic math to deduce the geometric shapes defined by those points.
If you use CGContextAddCurveToPoint your user could make curved lines defined by known points, and I’m pretty sure that those lines would run through the points, so you could still use basic math to determine at least an approximation of the types of shapes formed.
But if you use CGContextAddQuadCurveToPoint, the points define a framework outside of the drawn curve. You’d need more advanced math to determine the shapes formed by curves along tangents.
Gelphman also discusses “Path Utility Functions,” like getting a bounding box and checking whether a given point is inside the path.
As for moving the completed paths, I think you would use CGContextTranslateCTM.
Hi Guys I am doing some work on iOS and the work requires use of OpenGL es. So now I have a bunch of squares, cubes and triangles on the screen. Some of these geometries might overlap. Any ideas/ approaches for touch detection?
Regards
To follow up on the answer already given, squares, cubes and triangles are convex shapes so you can perform ray-object intersection quite easily, even directly from the geometry rather than from the mathematical description of the perfect object.
You're going to need to be able to calculate the distance of a point from the plane and the intersection of a ray with the plane. As a simple test you can implement yourself very quickly, for each polygon on the convex shape work out the intersection between the ray and the plane. Then check whether that point is behind all the planes defined by polygons that share an edge with the one you just tested. If so then the hit is on the surface of the object — though you should be careful about coplanar adjoining polygons and rounding errors.
Once you've found a collision you can easily get the length of the ray to the point of collision. The object with the shortest distance is the one that's in front.
If that's fast enough then great, otherwise you'll probably want to look into partitioning the world or breaking objects down to their silhouettes. Convex objects are really simple — consider all the edges that run between one polygon and the next. If only exactly one of those polygons is front facing then the edge is part of the silhouette. All the silhouettes edges together can be projected to a convex 2d shape on the view plane. You can then test touches by performing a 2d point-in-polygon from that.
A further common alternative that eliminates most of the maths is picking. You'd render the scene to an invisible buffer with each object appearing as a solid blob in a suitably unique colour. To test for touch, you'd just do a glReadPixels and inspect the colour.
For the purposes of glu on the iPhone, you can grab SGI's implementation (as used by MESA). I've used its tessellator in a shipping, production project before.
I had that problem in the past. What I have used is an implementation of glu unproject that you can find on google (it uses the inverse of the model view projection matrix and the viewport size). This allows you to map the 2D screen coordinates to a 3D vector into the world. Then, you can use this vector to intersect with your objects and see which one intersects (or comes really close to doing so).
I do hope there are better ways of doing this, so I look forward to other answers as well!
Once you get the inverse-modelview and cast your ray (vector), you still need to know if the ray intersects your geometry. One approach would be to grab the depth (z in view coordinate system) of the object's center and extend (stretch) your vector just that far. Then see if the vector's "head" ends within the volume of your object or not (you need the objects center and e.g. Its radius, if it's a sphere)
I'm using Geoserver version 2.1.1, Postgres 9 and PostGIS 2.0
What I want to achieve should (i think!) be quite straight forward. I want to render on a map a line that represents the Great Circle between two cities on the earths surface.
My database contains the city locations represented as geography points defined as latitude and lonfitude pairs.
I have a layer defining an SQL view in Geoserver which retrieves a linestring (st_makeline) from the two coordinates for the specified cities. I'm having to type cast the geographies to geometries to get this to work.
But when I draw the returned line on a map what i get is a straight line and not the curved line that I am expecting.
Can someone tell me how I should be going about this?
Thanks!
PostGIS offers mainly "constructors" of the base geometries point, linestring and polygone, like ST_MakeLine.
And what yo uwant to do depends also on the coordinate reference system you use when displaying your map layers.
Here's a nice trick about great circles or parts of:
https://gis.stackexchange.com/questions/5204/curved-point-to-point-route-maps
Yours, Stefan
P.S. Here's some related stuff:
Drawing circles on a sphere
And here's some math:
http://www.mathworks.ch/matlabcentral/newsreader/view_thread/277881
I had a similar problem in cartodb (which also uses PostGIS); I wanted to get curved lines from straight lines. Maybe this post can help.