Research Experience Daniel Fregosi Summer 2006 UNCC Visualization Center

 Worked under the guidance of Dr. Ribarsky and Dr. Wartell  Thanks to Remco Chang, Hunter Hale, and Josh Jones for their everyday help

Virtual Charlotte  3D Model System for the City of Charlotte  Basic concept similar to Google Earth  Used to attract businesses and people into moving to the Charlotte area  Visually pleasing  Completely interactive

Model of UNCC Campus with Textures and Elevation Model taken from UNCC Viscenter

Overview of My Part  Extract building footprints from geography data we were given  Create program to view and edit footprints  Clean up and process the data  Output the data for optimal access and rendering

Parsing the Data  Footprints were in Shapefile format  Did not allow access or modification, only viewing  Wrote a parser to get all of the points and contours out and stored into customized data type

Parsing the Data  File was in binary format rather than ASCII  Had to learn about computer organization  How data is stored (number of bytes, big vs. little endian)

Viewing the Building Footprints  Create simple viewing program  Visualize data to check for correctness  Gave buildings random colors to differentiate  Gave buildings random height to be able to visualize the entire city in 3D

Viewing the Building Footprints  Functionality needed:  Zoom in and out  Scroll through and rotate the map  Focus in on predefined list of certain buildings  Identify and center in on buildings by clicking on them

372,455 Buildings

Viewing the Building Footprints  Open Graphics Library – standard environment for developing 2D and 3D graphics applications  Utilized display lists – store rendering information on video card for increased performance

Cleaning Up the Data  There were many problematic building outlines that required fixing  Define, identify, and corrected problems

In line vertices (3 or more)  If the angle formed between 2 edges is between 170° and 190°, middle vertex is deleted 60,493 In Line Vertices Erased out of 2.9 Million

Sharing multiple vertices  Corrected first  Merged into one building  5,101 cases

One vertex in common  Separate common vertices by small amount  3,588 cases cases

Intersecting buildings  Crossing edges, coincident edges  Merged into one building  1,438 cases

Completely Surrounded Buildings  Corrected last so all of the other cases were out of the way  Deleted footprint on the inside, 606 cases

Cleaning Up the Data  Researched geometric algorithms for detecting these situations  Practiced strategies for decreasing the run time of these algorithms  Only running tests if buildings are within a certain distance

Packaging and Output  Convert all of the complex polygons into series of triangles using OpenGL’s tesselator  Why triangles?  Most efficient for rendering  Simple, convex polygons  Can apply textures to them easily  Easy to package  Saved data to binary format  Documented simple yet efficient format for future use

Biggest Challenges  Learning new languages  C++  OpenGL  Conducting graduate level research for the first time  Freedom to explore new ideas  Testing new concepts