On Wed, Mar 17, 2010 at 09:56:14PM -0700, Alexander Solla wrote: > I wrote this to Darrin, but didn't CC cafe: > > On Mar 17, 2010, at 9:20 PM, Darrin Chandler wrote: > > >type Cartesian_coord = Float > > > >type Latitude = Float > >type Longitude = Float > > > >data Point = Cartesian (Cartesian_coord, Cartesian_coord) > > | Spherical (Latitude, Longitude) > > > >type Center = Point > >type Radius = Float > > > >data Shape = Circle Center Radius > > | Polygon [Point] > > > >This obviously stinks since a Polygon could contain mixed > >Cartesian and > >Spherical points. Polygon needs to be one or the other, but not mixed. > > My suggestion would be to use an alternate representation of > "spherical" points in terms of polar coordinates, and then to > normalize and mix at will: > > type Theta = Float > type Radius = Float > > data Point = Cartesian (Cartesian_coord, Cartesian_coord) > | Polar (Theta, Radius) > > normalize_point :: Point -> Point > normalize_point Cartesian x y = Cartesian x y > normalize_point Polar t r = Cartesian x y where x = r * cos t; y = r > * sin t; > > It really depends on what you want to do with your points. If you > want to do linear algebra, you might want your points to depend on a > basis, for example. But your "spherical" points don't really form a > basis in three-space, or even over all of two-space.
I see what you mean, but I don't think that's what I need. I want to have keep Lat/Lon, as I may have large groups of shapes in Lat/Lon and want to do things with them as is. And the same for cartesian coords. Sometimes I will translate betweem lat/lon and cartesian, but many times I will be doing calculations in "native" coordinates. But it's a nice technique you show, and it will come in handy elsewhere. -- Darrin Chandler | Phoenix BSD User Group | MetaBUG dwchand...@stilyagin.com | http://phxbug.org/ | http://metabug.org/ http://www.stilyagin.com/ | Daemons in the Desert | Global BUG Federation
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