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Member Since 02 Mar 2004
Offline Last Active Mar 14 2015 04:44 AM

Topics I've Started

Cutting polygons by a grid.

08 January 2015 - 08:02 PM

I'm trying to cut polygons into smaller polygons constrained by a grid. I'm wondering if there's a fast way to do this other than normal poly-poly clipping because I'm dealing with a large amount of points on a comsumer's computer (via javascript).


The application is that I want to cut country boundries by longitude and latitude lines before tessellating them so they don't get clipped by the sphere that they will be matted on. If I don't do this then large triangles will go inside the sphere.

Frustrum Culling Tiled Sphere

24 August 2014 - 02:25 AM

I'm making a planet renderer, kind of like Google Earth. I want to implement tiling, so that different parts of the map can load like in Google Maps when you pan or zoom in or out. I'm having a hard time figuring out how to figure out what areas of the sphere exists in the view frustum and should be loaded or displayed.


Any suggestions?



Properly rendering a starfield skymap

23 July 2013 - 01:05 AM

I'm trying to render a starfield properly. I'm doing something similar to the new google maps zoomed out where you can see the entire planet and stars. However, right now in my implementation i'm basically drawing a sphere with the stars in the scene. When you zoom in or out the stars get zoomed in or out, but i think the right implementation is that they don't move. How would I properly render that?


basically right now the sky is a sphere(5000), and the earth is a sphere(10) and the camera moves in and out looking at the earth. when i zoom in, a narrower area of the sky is shown, I don't think this is correct, is it? Would I scale the sky inversely to the camera zoom? -> the more the camera is zoomed, the smaller the sky is?

Space Partitioning on Sphere

01 June 2013 - 01:27 PM

What approaches would be best for space partitioning on a sphere? I'm working with a visualizing data on the surface of the earth.


Some operations that would be relevant

  • Find the closest stored point to a given point
  • See if a the given point is within a region
  • Adding and removing points and regions


Currently, some of the approaches that I've thought of taking are:

  • Start with a octahedron and do triangle tessellation, 4 triangles to each parent triangle. I'm not sure how to approach indexing nodes from latitude, longitude. The pros would be that the partitions would be basically equal area.
  • Quadtree, with the first level separated by north/south hemisphere (positive/negative y) and then a normal quadtree based on the x, z coordinates. This might be a bit easier to index, but leaves might not be balanced well.

Are there any other common approaches that you guys know of or can think of?



Finding the area of a geopolygon (made of longitude latitude points)

04 April 2013 - 05:27 AM

How would you go about, or does anyone know of any articles/references on calculating the area of a polygon? (Remember that maps are distorted towards the poles, to the actual area isn't just the polygon area) Or any suggestions on how I might go about calculating this?