Surface Functions

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Surface Functions

• FE 423 - Lecture 2b

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From TuesdayGridding contours and contouring
grids
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From Tuesday

• HJ Andrews Topography
• Download
• Import71.exe
• TOPOGRID

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SCHEDULE
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OUTLINE

• Why Slope, Aspect, Curvature
• Slope/Aspect/Curvature in GRID
• Hillshade

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SLOPE

• What is Slope?
• Why do we care about slope?
• How do we define slope?
• With points?
• On TIN?
• On Contours?

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ASPECT

• What is aspect?
• Why do we care about aspect?
• How do we define aspect?
• With points?
• On TIN?
• On Contours?

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CURVATURE

• What is curvature?
• Why do we care about curvature?
• How do we define curvature?
• With points?
• On TIN?
• On Contours?

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Surface Functions in GRID

• Z Ax2y2 Bx2y Cxy2 Dx2 Ey2 Fxy Gx
  Hy I
• Z(0,0) I
• Z(0,1) E H I
• Z(0,-1) E - H I
• dZ/dx 2Axy2 2Bxy Cy2 2Dx Fy G
• d2Z/dx2 2Ay2 2By 2D

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SLOPE IN GRID
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ASPECT IN GRID
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CURVATURE IN GRID
A (Z1 Z3 Z7 Z9) /4 - (Z2 Z4 Z6
Z8) /2 Z5 /L4 B (Z1 Z3 - Z7 - Z9) /4 -
(Z2 - Z8) /2 /L3 C (-Z1 Z3 - Z7 Z9) /4
( Z4 - Z6) /2 /L3 D (Z4 Z6) /2 - Z5 /L2 E
(Z2 Z8) /2 - Z5 /L2 F (-Z1 Z3 Z7 -
Z9) /4L2 G (-Z4 Z6) /2L H (Z2 - Z8) /2L I
Z5 Curvature (D E) /2
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CURVATURE IN GRID
In ArcGRID Cgt curve_grid curvature(dem,
out_pro_grid, out_plan_grid, out_slope,
out_aspect) Surface Analyst aGrid.Curvature
(proCurvFN, planCurvFN, slopeFN, aspectFN)
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CURVATURE
out_slope out_aspect out_pro_grid
out_plan_grid
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HILLSHADE

• Angle of sun to the surface
• examples
• radiation on snowpack
• radiation on stream
• rain shadow

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Reading from ArcDoc

• Spatial modeling
• Cell-based Modeling with GRID
• GRID algebra and analysis environment
• GRID operators
• GRID map algebra rules and syntax

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Discussion Problems

• Use a sun-angle calculator from the web to
  identify the sun angle for the beginning and end
  of this class period. Make a hillshaded image of
  the UW area for these times.
• Using a DEM of steep topography, map the areas of
  steep and convergent topography.

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Practice Problem 1 Identify the slope of each
square
500m grid
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Practice Problem 2 Identify the aspect of each
square
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Practice Problem 3 Estimate slope for each
cell
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Practice Problem 4 Estimate aspect for each
cell
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Practice Problem 5 Shade convergent
topography
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Practice Problem 6 Shade convergent topography