Digital Topography

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Digital Topography

• FE 423 - Lecture 2a

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From Last Week

• Grid the roads and stands using various grid
  sizes. Overlay and comment.
• Grid the stands, roads, and landslides to match
  the DEM grids. Do they line up?
• Overlay the road lines on the road grid. Comment.
  
• Repeat with polygons.

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Which of majority, centroid, or weighted are most
similar to the others? Are they more similar on
large or small grid cells?
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SCHEDULE
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OUTLINE

• Representing topography
• Converting topography to grid
• Digital topography sources

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FIRST...

• Out onto the lawn!
• Bring your jacket (or not)
• Enjoy the view! ...wish you were an
  oceanographer?
• How do we represent the topography?

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DIGITAL TOPOGRAPHY points, arcs, polygons, grids
We can survey point elevations We can make
contours of equal elevation or make polygons of
elevation range or a grid with elevation at each
node
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Digital Elevation Data vs. DEM

• we collect data at points
• all points between must be modeled
• hence, Digital Elevation MODEL

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Modeling Digital Elevation Data

• Connect the dots
• TIN - triangular irregular network
• Spline - minimum curvature fit
• IDW- inverse distance weighting
• Approximate
• Trend - regression

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Digital Elevation Data Sources

• Points
• you might survey your own
• Contour lines
• popular old tool
• requires ArcInfo TOPOGRID
• Raster DEM
• ASCII
• USGS

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ASCII Raster GRIDs
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Getting Topographic Data

• Importing Raster data
• Import Data Source...
• Importing ArcInfo exported files
• Cgt IMPORT71.exe coverage.e00

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Reading from ArcDoc

• Spatial modeling
• Cell-based Modeling with GRID
• Surface functions
• CURVATURE
• LATTICEDEM
• TOPOGRID

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Discussion Problems
Go to Harveys 10-meter DEM page http//duff.geolo
gy.washington.edu/data/raster/tenmeter/byquad/inde
x.html Download, unzip, import, and display a
quad that you are familiar with Create contours
and a hillshade image Find on the web the HJ
Andrews data we have been using, download,
import, and display.
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Practice Problem 1 Identify the elevation of
the center of each square
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Practice Problem 2 Draw 100 meter contour lines
from these elevations