   Terrain LOD and seamless navigation
  Hi all,Have some questions on terrain rendering... hope you can give some advice. Thanks in advance.I am on a simulation project which objective is to use real world map information to generate 3D terrain and fly-through navigation. Currently, the maps (GIS file format, *.DEM) comes in separate grid area of different resolution and size. Other complications include the fact that the earth is not perfectly round.I understand that in the gaming world, this terrain rendering technique has already been around for very long. I hope to get advice on the possible ways to load and render an expansive terrain such as in MMORPGs like World of Warcraft. 1. The entire continent (e.g. Kalimdor) is so large. So then what are the ways to store the terrain information? Is it also in separate files according to zone? Or is it just one giantic binary file store ALL the vertices?2. If it is one big giantic file, then to me, determining which vertics to render is really expensive because I have to iterate through all the points to calculate some radius distance from my current position. And then there is another issue of reordering the vertices into triangles for rendering.3. If it is separated by zones, I could load the entire zone into RAM and draw all of it whether or not it is visible? But then how is the transition from zone to zone so smooth. What are the possible ways to merge 2 zone terrain data so semalessly?Apprecuate any advice thanks thanks.   
  in WoW..each zone has its own heightmap in its own file.  when a user comes close to the border of another zone, that zones heightmap is loaded also and the parts that are visible to you are drawn   