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The 3DIMap technology for the Web
The production process of 3D contents
1. Mesh processing and production of terrain models2. Image processing for textures3. Integration with database and custom 3D models4. Distribution and visualization of 3D scenesIs there a resolution limit?
The phases of the production process of 3DIMap contents are shown in the diagram shown on the right.
All these steps are highly automatized, in order to achieve precision and fast production. Here we give some detail.
Three-dimensional
meshes are built from digital elevation data (DEMs); at this stage the meshes
usually have a huge amount of vertices for a web delivery and a real-time
rendering (for instance, a square region of 300 km with horizontal resolution
of 1 km, gives a mesh with 90000 vertices); thus some optimization process
is needed.
A reducing mesh algorithm, specifically designed for landscape meshes, reduces
the number of vertices; terrain details are maintained while obtaining reduction
factors of the order of 20 or more.
The resulting mesh is then converted in the chosen planar projection (Lambert,
UTM, etc.), or directly computed in spherical coordinates.
Landscape textures are derived mainly from satellite images, aerial photos,
other raster graphics (topographic maps). Satellite images are often composed
by 7-8 layers corresponding to various bands of the visible and infrared
spectrum. In Landsat images, bands 1, 2, 3 (blue, green and red components)
are suitable to give true color appearance.
Texture images are then transformed into the chosen geodetic projection;
if multiple images are needed, they are joined through an algorithm that
a) finds the best superposition matching, b) equalizes the colors among
overlapping images, to avoid discontinuity on the common boundaries. According
to geographic coordinates of original images, the texture are precisely
positioned on the mesh, and all texture coordinates are calculated. In order
to optimize rendering speed, and to allow web streaming and multi-resolution
texturing, each mesh texture is properly subdivided in tiles, and compressed
as needed. 
The dynamic nature of 3DIMap contents makes easy to connect external databases and in general with systems providing data even in real time.
Additional 3D models, edited with modeling programs, such as 3D Studio Max®, can be added to the scene by means of programming or manual procedures.
3DIMap makes available two solutions for the delivery and visualization of 3D contents:
TrueFlight, based on Shockwave3D technology (Windows® and MacOS®
platforms), which let the user enjoy the best experience: he/she can freely
fly in the 3D world, and interact with all objects; images are rendered
on the client computer, by means of PC graphic hardware (Min. requirements:
300 MHz processor, accelerated graphic card with at least 8 MB of video
RAM).
Rendering Server, where images are created on a server and delivered in
jpeg format; the user can still move and interact, but less smoothly compared
with the previous solution. The main advantages of this approach is the
immediate access and use from all platforms, including handhelds. For an
example, click here. 
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