Introduction to 3D Data

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.