“3-D” & Temporal GIS

GIS is still mainly 2-D …

Horizontal sure, but …. how to deal with elevation/depth or time –Vertical Horizontal and vertical Horizontal, vertical, and time

You knew I had to mention it… GOOGLE EARTH

ArcScene Demo

The Vertical Dimension two very different ways of looking at representations of the vertical dimension (third dimension) in GIS “2.5-D” and “3-D” vertical dimension combined with temporal query = “4-D”

“2.5 D” most common way of “doing 3D” in commercial GIS packages z value (normally elevation) is recorded as an attribute for each data point (x,y) z values can be used in a perspective plot to create the appearance of 3 dimensions not true 3-D representation because elevation is not an independent variable

2.5 D Representations attractive way of displaying topography and other continuous surfaces from DEMs or TINs perspective plots computed from any viewpoint additional layers "draped" over the surface using color

“Coastal Terrain Model” + = Integrated Topo-Bathy Model Bathymetry Topography …a surface that integrates topography and bathymetry

Satellite Imagery Draped on Topo-bathy model

Boundary Representation TIN is a 2.5 D type of B-rep, constrained to be single-valued (i.e. one value of z for every x,y) objects are defined as polyhedra bounded by planes or faces each object can be represented by a number of faces, edges, points

Perspective Plot from TIN ( 2.5-D B-Rep )

B-Rep of a Cave Passage

B-Reps requires a powerful user-interface to construct combinatorially-complex objects planes, edges, points –define carefully and consistently – maintain validity performance degrades rapidly with high geometric complexity

True 3-D store data in structures that actually reference locations in 3D space (x,y,z) here z is not an attribute but an element of the location of the point if z is missing, object does not exist! several z’s possible for a single x-y pair, –soundings in the ocean or atmosphere, geologic logs of wells

3-D Applications geological/geophysical exploration engineering design of mines, quarries, dams, reservoirs, etc. scientific explanation of 3D processes such as ocean currents or lava flows –“data driven” - may not necessarily know what you will find in 3D –so the structure of the representation may enhance types of analyses that can be performed

STRATAFORM GIS, N. Calif. Fonseca, Mayer, and Paton in Wright (ed.) Undersea with GIS, ESRI Press, 2002

“Fledermaus” Interactive Visualization Systems

Volumes visualization of volumes modeling of volumes –algorithms for 3D spatial analysis simpler, more efficient, if data in a volumetric form

Hydrothermal Plume model output VTK/Java3D allows volume calculations, rendering, and analysis. ● 3D probe ● animation ● bathymetry ● multibeam ● Smith/Sandwell Slide courtesy of Tiffany Vance, NOAA

Spatial Occupancy Enumeration ( SOE ) volume is divided into cubes or voxels usually produced by converting from B- reps (similar to converting vectors to rasters in 2D) properties like mass, volume and surface area are quickly computed as Boolean operations [on (full) / off (empty)] or voxel counts

SOE of a Mine/Quarry

Commercially Available? Research frontier not too many truly 3D GIS packages on the market 2- or 2.5D GIS linked to 3D modeling package Gaming industry way ahead

Time Dependence time dependence adds a third dimension to spatial data, just as the vertical dimension does or may be added to 3 spatial dimensions to give 4D

University of Hawaii, School of Ocean Earth Science and Technology Plate Tectonics (x,y,t)

Coastal Evolution of OR/WA Cross & Twichell, USGS Woods Hole in Wright (ed.) Undersea with GIS, ESRI Press, 2002.

Time and Geographical Data computer science has dealt with time dependence of records in databases –e.g., records may be valid only for limited times geographical cases are more complex - –objects may have limited existence, but may also move, change shape, and change attributes database models for time? few “temporal GISs” on the market –Tracking Analyst for ArcView

Dealing with Time in GIS 1 - Shapes of Objects Change shapes of objects change through time define a limited number of time "slices" store the objects at each slice objects may coalesce or split from one time slice to the next –e.g. kelp beds off the Oregon coast or use a 3D space with the vertical dimension as time, populated by 3D objects (4D)

2 - Attributes Change attributes of objects change through time define a limited number of time "slices" store the attributes as separate tables for each time slice if attributes are needed between time slices, interpolate

3 - Boundaries Change boundaries between objects change through time boundaries may turn “on” and “off” rather than move the system stores all boundary lines which ever existed then reconstructs objects from the boundaries at any given time

Centennia Atlas