Post on 19-Jan-2015
description
Introduction to 3D
GeovisualizationJohn 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 essentially 3D 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.
• Stanford Bunny69,451 polygons.
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.