Introduction to 3D Geovisualization John Reiser
History• Computer rendering of 3D images is a relatively recent development.• 3D rendering requires considerable processing to generate photorealistic images.• Until capabilities rose and costs dropped, 3D rendering was often a task left up to supercomputers.• One of the first 3D models: “Utah Teapot”
Utah Teapot• Designed and rendered by Martin Newell in 1975 at the University of Utah.• A standard white Melitta tea pot.• Originally didn’t have a bottom.• Reference data for testing new applications.
3D Rendering• Let’s cover some basics behind 3D rendering.• Several methods for drawing the 3D object.• Constructing a model out of triangles.• Rendering methods can be refined further with textures and lighting effects.
Wireframes• Most basic method of rendering a 3D object.• Vector representation of a 3D object from a specific vantage point.• Edges are shown with simplified faces.
Textures• Textures are applied to the faces of a 3D model.• Textures can be a solid color, image or photograph.• Textures can include additional data, such as noise, reflectivity or bumps.
Raytracing• Rendering method employs algorithms to simulate individual rays of light and how they interact with the object and the environment.• Light, shadows, focus, etc can be modeled.• Highly photorealistic.
Polygon Rendering• The edges and faces are • Stanford Bunny essentially 3D polygons. 69,451 polygons.• The more complex the polygon, the longer the rendering time.• The simplest polygon is the triangle.• Many renderers utilize triangles to construct a 3D model.
Triangles & TINs• Back to GIS, triangulated irregular networks are digital elevation models based on nodes & edges that form a mesh of triangular faces.• Rendering landscapes instead of objects requires georeferencing.
TINs versus Raster DEMs• TINs allow for greater variation in the terrain than raster.• Raster cell sizes must be small to capture minute variations, producing larger files.• Gentle changes need only a few triangles to be represented.
Building Models• Wireframe models can be covered with an architectural rendering or a photograph to create a basic building model.• Details can be introduced by adding more textured faces to the volume.
Building Information Modeling• Highly detailed models of buildings, down to interior spaces. – HVAC, mechanicals, etc.• Used for facilities management.• Used to visualize maintenance, planning and construction efforts.• GIS for buildings.
Viewing 3D• Several methods of viewing 3D images on a 2D surface. – Shutters – Anaglyphs – Free (cross eyes)• Some 3D rendering software will create anaglyphs for you.