Lately, I am back to terrain rendering. I am looking for solutions to
common problems in displaying aerial images on sampled heightfields. You
all know these techniques from terrain viewers like Google Earth.
The work focuses on improving the visual quality of the terrain. The TeReX
renderer uses the tiling approach from Jens Schneiders Terrain paper with a number of improvements:
TeReX has been used for displaying the heighfields in the river simulation project (image on the left).
- each tile is meshed into a single triangle strip; no need for
primitive restart tokens
- the tiles are managed by a caching system that feeds the GPU with
necessary geometry and texture LOD data with a look-ahead estimation of
the camera movement
- the tile texturing can overlay several textures (for annotations,
roads and other infrastructure from topographic maps)
- the renderer can project planar geometry (road splines, buildings)
onto the heightfield
- the renderer can show GPS tracking data
- support for processing data from an HRSC device
Recent features under development:
||Fighting the curtain effect
Because the terrain textures are usually photographed from far above with
the camera pointing straight down, vertical surfaces like the walls of a
house or the lower leafs of vegetation are not visible. When rendering
them on a heightfield, these vertical surfaces look like curtains.
The HRSC device is a scanning camera that has additional
side channels that are usually used to reconstruct a heightfield. Because
these channels look "ahead" and "backwards" with an
angle, they can see the side views of objects. The TeReX renderer can look at
the orientation of the triangles of the heightfield and chooses the two best
projecting views with a weighted blend. The channels are greyscale, so it
needs to synthesize color from the nadir (= straight from above) view
using a LAB color model calibrated to a D65 source. The reconstruction is
performed entirely in a GPU shader.
See the images in the archive for an example of how views of house facades
and trees are improved.