Edge Conditions: Tiles

The basic idea of a tile system is simple, elegant and workable: You take a large area, divide it into smaller areas and show one at a time.

Os course we had to go and complicate this process. It turns out that one tile just does not hold quite enough information nicely. Each tile is 256 x 256 pixels. Showing such a tile on a 2500 x 2000 monitor means that either the tile is tile or looks very crude.

For the time being we are showing four tiles at a time to make a square that is 1024 x 1024 units per side. It would be nice t have more but this really begins to slow down on most machines.

It would be great to have nine tiles at once. Then, for sure, the center of attention could be placed on the center tile. With four tiles, it gets a bit tricky. Very often the thing you are looking for is very near a corner. So, for example, you can have three quarters of a city not showing. Thus there is a routine that add the three tiles to the edges closest to the point in question.

This works fine for zoom levels 2 to 7, but above that the interpolation routine kicks in and you know have a situation where you have a window(1) on a window(2) of the world. Well, sometimes window 1 wants to sit over two window 2s or when window 1 is over a corner it wants to sit over 4 window 2s.

An then there is the international dateline and you have to start all over again.

Little by little or actually edge by edge, these situations are being dealt with. Are they bugs? Not really. They are the system behaving exactly as it was told to behave. And so now we must give further more detailed instructions.

It's a fun little game of logic. So every time you see a tile that is flat or has not yet been updated from the previous view you can think we still have some more fun ahead of us.

Note: this page should go to the Terrain Viewer repo...