GLOBAL FLOOD SCENARIO:  MODEL GENERALITY

The Argo Dam holds back the Huron River, just to the west of downtown, forming Barton Pond.  Allen Creek enters the Huron River just to the east of the Argo Dam.  What would be the impact of a sudden disaster at Argo Dam on the homes and businesses in the Allen Creek floodplain?  How might one model such a scene?

The City of Ann Arbor already has a substantial amount of data in its technological base.  Much of it can be analyzed using GIS (Geographic Information Systems) software.  Questions such as how many homes lie in the floodplain, which parcels have their centroid in the floodplain, and numerous other questions linking databases to maps can be answered.  Also, clickable maps may answer related questions in planning for evacuation or analysis following an emergency.  Beyond these maps, however, much more can come through virtual reality models.  The images below show some maps made in the GIS; all are 2D maps although some show buildings extruded from digitized footprints of aerials as 3D suggestions.
 
 

Buildings in relation to the Allen Creek floodplain.  Buildings are extruded in relation to underlying elevation, as are streets and hydro features.

Buildings in relation to the Allen Creek Floodway.  Buildings are extruded in relation to underlying elevation, as are streets and hydro features.

Contours, Allen Creek, 1 foot contour interval (spacing in elevation between successive contours).  Contours are extruded in relation to underlying elevation, as are streets.

Contours and buildings, Allen Creek.  Buildings and other features are extruded in relation to underlying elevation.

Contours, buildings, and floodway, Allen Creek.  Buildings and other features are extruded in relation to underlying elevation.

Contours, buildings, floodway, and floodplain, Allen Creek.  Note coplanar polygons interfering with distinction between floodway and floodplain.  Buildings and other features are extruded in relation to underlying elevation.  The problems associated with coplanar polygons are not unique to virtual reality models!

Triangulated Irregular Network (TIN), formed from 1 foot contours, in the GIS (a specific tesselation strategy).  These files typically have far to many triangles to be useful for broad studies portrayed on average equipment.  The level of detail in the TIN matches the level of detail in the contour files (note the street outlines and related features).  On a fine machine, this TIN can be converted to a 3D file which can then be exported to vrml 2.0.

The image below shows a close up of the figure with buildings extruded in relation to the TIN (in previous files, buildings were always extruded in relation to the TIN, but the TIN generally was not shown to reduce file size).   With a very local study, it is possible to show the TIN, as well.  Click on the image below to launch the associated vrml file derived directly from the GIS.  Notice that viewpoints will need to be set:  the view within the GIS was attractive but when the file was converted to vrml, that view was lost.   The sun was set at low in the southeast, within the GIS.  No vertical exaggeration was calculated within the GIS (although it can be done).   To keep everything working smoothly, it is often easiest simply to use the GIS file as a way to introduce information into 3D Studio Max and extrude buildings as boxes in relation to contours.  Then, perhaps, make an elevation grid in 3D Studio Max from the contours rather than trying to incorporate the TIN directly into the vrml file.  This VR is composed of a number of inline files:  these are attached in the subdirectory associated with this link (take a look to see the complexity...open them in Notepad or VRMLpad).

Imagine then, clicking on a link in a broad scale map to see virtual models of associated street intersections or blocks.  Then, imagine clicking on buildings in the vrml file to "look inside" the buildings.  Keep that in mind when considering the section below.
 
 

LOCAL FLOOD SCENARIO:  MODEL DETAIL

Consider the impact that Liberty Street has on possible flood scenarios:  Liberty, itself, serves as a dam in the event of a surge up the Allen's Creek.   In the map below, the Allen Creek "floodway" (the channel that holds the creek, underground much of the way, but it's still there) is shaded in cyan diagonal stripes.  The Allen Creek "floodplain" (the area that catches the overflow in the time of flood, much as a saucer catches fluid from an overflowing cup) is shaded in medium blue diagonal stripes orthogonal to the cyan stripes.  The solid shading underneath reflects shading from a "Triangulated Irregular Network (TIN)" formed in the GIS from the City contour map (contour interval of five feet).  Look at the intersection of Liberty and the Allen Creek floodway.  Look east to Ashley, where the TIN turns green.  Now look to the west, to Fourth, where the TIN once again turns green.  The rise to the east is much sharper than is the rise to the west.  Thus, the rise of Liberty to the east, to Ashley, serves as a dam, forcing water farther to the west.  Look at how many structures there are to the west!  This small example, when carefully realized as VR (coupled with sound effects) and played out in the CAVE and elsewhere, might have the power to convince municipal authorities in Ann Arbor to make policy decisions involving floodplain management that could have positive long-run implications in terms of human welfare and safe-guarding of infrastructure and property...consider the recent case in New Orleans...

Students will be provided with basic geometry formed in a GIS to be manipulated using VRML-Pad or 3D Studio Max.  That geometry will be formed from city maps, by the lead faculty member, using GIS to analyze city files and to produce both flat maps and vrml files directly from the GIS.
 

The creation of a virtual downtown has environmental and public policy implications in a number of directions.  Build on existing successful work that has already seen substantial use by the City of Ann Arbor municipal government.

• General models have seen substantial use by the Downtown Residential Task Force of the City of Ann Arbor.  For the purposes of studying height in the downtown, a general, approximate model was sufficient for initial guidelines.
• Students in ENG477 over the past two years have worked on applying textures to the general model and in improving its accuracy.  A sample is shown as a static image below (a view looking east on Liberty Street:  the intersection with the traffic light is Main and Liberty).  This screen capture is from the model created by Kwon, Lazzaro, Oppenheim, and Rosenblum, and modified by Beier.  To find others, follow the link above.

 
• The model is a good use of Virtual Reality because it meets the following "Criteria for VR Applications" (from Prof. Beier's lecture notes) although it meets some more clearly than it meets others:
• Complex, Three-Dimensional Geometry
understanding, evaluation, error detection, exploration of alternatives
• Complex Behavior and Functionality
dynamic processes, simulation, training, understanding, evaluation, error detection, exploration of alternatives
• Non-Existing or Not-Yet-Existing Worlds
planning in general, virtual prototypes, past or future objects, places and events, creative work of abstract nature (insofar, perhaps, as ordinance revision and other revision of city or legal code, involving air rights and other issues, could eventually become involved).
• Invisible or Hidden Worlds
(water management that cannot be seen but only imagined).
• Remote Locations
(adding height in the downtown may come about, in part, as a result of purchasing development rights elsewhere to conserve green space outside town)
• Dangerous Situations:  sound will serve as an important added audio descriptor
• Preservation of Resources
• Cost and Time Savings
• Communication, Demonstration, Promotion
• Excitement and Fun
• Steps that will continue beyond this term involve
• Completion of the detailed and general models
• Implementation of the models, by the City, in a systematic manner.
• Continued effort to gain funding of work.
• Extension to other communities of the materials generated for Ann Arbor.