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ArcView 3-D Analyst
Triangulated Irregular Network (TIN)
A Mesh of Triangles
Triangle is the onlypolygon that is always
planar in 3-D
Points Lines Surfaces
Tin Triangles in 3-D
(x3, y3, z3)
(x1, y1, z1) (x2, y2, z2)
x
y
z
Projection in (x,y) plane
Delauney TriangulationMaximize the minimum interior angle of trianglesNo point lies within the circumcircle of a triangle
Yes No
Circumcircle of Triangle
• Draw the perpendicular bisectors of each edge of the triangle
• Circumcircle is centered on their intersection point
• Radial lines from center have equal length
Inputs for Creating a TINMass Points Soft Breaklines Hard Breaklines
• Hard breaklines define locations of abrupt surface change (e.g. streams, ridges, road kerbs, building footprints, dams)• Soft breaklines are used to ensure that known z values along a linear feature are maintained in the tin.
TIN for Waller Creek
TIN with Surface Features
Classroom
Waller Creek
UT FootballStadium
A Portion of the TIN
Input Data for this Portion
Mass Points
Soft Breaklines
Hard Breaklines
TIN Vertices and Triangles
TIN Surface Model
WallerCreek
Street andBridge
3-D Scene
3-D Scene with Buildings
Watershed Modeling With TINs
Slides from Dr James NelsonBrigham Young University
Sponsored by National Highway InstituteUS Department of Transportation
Work Flow
Tin-basedWatershed Delineation
Flow On a Triangle
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Flow On a TIN
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Defining Basins
Computing Basin Data• Area• Slope• Flow Distances
– Slopes
• Aspect• Stream Lengths
– Slopes
• Others
A=3.18 acr BS=0.0124 ft/ft AOFD=140.06 ft
A=5.39 acr BS=0.0243 ft/ft AOFD=158.33 ft
A=7.21 acr BS=0.0200 ft/ft AOFD=93.47 ft
Add OutletsRefine Boundaries
Modifying Basins
Merge BasinsSplit BasinsDelete OutletsRecompute Data
A=15.78 acr BS=0.0199 ft/ft AOFD=123.29 ft
Ten Steps Using TINs 1. Background Elevation 2. Smooth Elevations 3. Conceptual Model 4. Redistribute Vertices 5. Create TIN 6. Edit TIN 7. Add Interior Outlets 8. Define Basins 9. Refine TIN10. Compute Basin Data
1: Background Elevation
• TINs– Digitized– XYZ Data
• DEMs
2: Smooth Elevations• TINs or DEMs
TOPAZContoursImageImporting
DXF
GIS
3: Conceptual Model
From Coarse to FineFrom Fine to CoarseUnequal Distribution
4: Redistribute Vertices
Conceptual ModelTriangulate
Enforce Breaklines
Interpolate Z
5: Create TIN
6: Edit TIN• Flat Triangles
• Pits
7: Add Sub-basin Outlets
8: Define Basins
9: Refine TINSplit FlowRefineNULL Triangles
10: Compute Basin Data
• Basins– Area– Slope– Avg. Elevation– Length
• Streams– Length– Slope
A=0.29 mi 2 BS=0.2450 ft/ft AOFD=279.69 ft
A=0.40 mi 2 BS=0.3065 ft/ft AOFD=674.92 ft
A=0.63 mi 2 BS=0.3552 ft/ft
AOFD=1222.43 ft
A=0.17 mi 2 BS=0.3730 ft/ft AOFD=589.46 ft
Ten Steps Using TINs 1. Background Elevation 2. Smooth Elevations 3. Conceptual Model 4. Redistribute Vertices 5. Create TIN 6. Edit TIN 7. Add Interior Outlets 8. Define Basins 9. Refine TIN10. Compute Basin Data
TIN Strengths• Automated Basin Delineation with Parameter
Calculations• “Adaptive” Resolution
– you can use most any elevation data source
• Urban Areas– where small variations in flow can be significant
• It Was in WMS First– reservoir definition, storage capacity curves, time area
curves, flood-plain delineation
TIN Weaknesses• Lack of Available Data
– With conceptual model approach this is not such a big factor anymore
• Extra Steps– Local editing
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