   the relief mapping methods
  hi, I am reading the real-time rendering . at the the relief  mapping part. the books says that one problem with relief mapping methods is that the illusion breaks down along the silhouette edges of objects. which will show the original surface's smooth outlines. I just can not understand the mean of "original surface's smooth outlines" . In my opinion ,In the edge, the detect of point which under the height will be missed because it is thin .So ,with the edge ,something after the edge will be see.Is that   "original surface's smooth outlines"?   
  I'm not sure what you're meaning, but think about a globe produced using a textured sphere with relief-mapping for terrain (e.g. mountains). Most of the side facing you will look okay, but when you look at the edge of the sphere, you'll see that it's smoothly curved because the bumpiness of the terrain isn't part of the geometry.   ; I'm not sure what you're meaning, but think about a globe produced using a textured sphere with relief-mapping for terrain (e.g. mountains). Most of the side facing you will look okay, but when you look at the edge of the sphere, you'll see that it's smoothly curved because the bumpiness of the terrain isn't part of the geometry. [/quote]I still can not understant that " it's smoothly curved because the bumpiness of the terrain isn't part of the geometry".. Can you explain it with more details?;  Relief mapping is a texturing trick. It doesn't actually change the shape of the geometry -- it only changes the way texturing is performed.If the object is made up of a single triangle, it's silhouette is made up of 3 straight lines. No matter how you texture that triangle, it's still got 3 straight edges.   ;  Pictures say a thousand words:The are both taken from a project I wrote on relief mapping, parallax mapping, displacement mapping, and more. The top picture is relief mapping with distorted silhouettes and the bottom is displacement mapped with the more accurate silhouette.   ;  For en excellent read with code included, check out http://upcommons.upc.edu/pfc/bitstream/2099.1/7717/1/Roi%20Mendez%20Fernandez.pdfThe page may take a while to load because the site is slow, give it time.   ;  If you're targeting more modern cards you can just use Quadtree Displacement Mapping. You can just let the ray exit the edges and discard the pixel in the shader. Pretty simple algorithm too.   ; thanks ,I think i should to write code to understand it in depth!   ;  The reason the illusion breaks down at steep angles is because the parallax and relief mapping techniques work by shifting the texture map coordinates to create the illusion of a perspective change.  The texture map coordinates cannot be pushed past the edge of the model, only along the suface.  When looking straight at the center of the model the texMap can be moved freely sideways as well as up and down.  At the edges of a sphere the texture map coordinates can move sideways but not up and down, instead they are now moving close and far.  Also we now have a situation that is like looking at a sheet of paper from the edge instead of straight on.  The illusion is created by the textureMap and it's coordinates position  and if  you can't see the image on the paper when looking at it's edge, you cannot see anything related to the image either, including the perspective shift.  N'est pas?   