Topographic Data

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Topographic Data

• Special Topic Presentation
• March 25, 2003
• Dana French

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Outline of Topics

• Terminology
• General Information
• Tools in ArcGIS used with 3D data
• 3D analyst
• Spatial analyst
• Demonstration in ArcScene
• Uses for 3D data

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Terminology

• Planimetric Map
• A map that represents the horizontal, but not
  the vertical, positions of the features
  represented

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Terminology

• Topographic Map
• A map that displays both the horizontal and
  vertical positions of the features represented
  distinguished from a planimetric map by the
  addition of relief in measurable form

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Information

• Topographic images enhance our view of many
  physiographic features, especially in relatively
  flat areas.
• One distinctive trait of a topographic maps is
  that contour lines are used to show the shape of
  the Earth's surface
• Contour lines join points of equal elevation on
  the surface of the land above or below a
  reference surface such as mean sea level.
• These lines allow the user to measure the height
  of mountains, depths of the ocean bottom, and
  steepness of slopes on the map.

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More Information

• Topographic maps provide information about the
  shape of a landscape, as well as its natural
  features and purpose built structures.
• Topographic data, also called 3D data must have
  some elevation attributes associated with it.

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Tools that can be used with topographic data

• ArcGIS
• Spatial analyst extension
• 3D analyst extension
• ArcScene
• A viewing tool

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The spatial analyst extension

• The Spatial Analyst functions allow you to
  create informative maps from your data
• Creating a hillshade to use as a backdrop of the
  terrain to support other data layers.
• Calculating slope, aspect and contours, or
  creating a map displaying visibility.
• You can use derived data together to help solve
  spatial problems.

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The 3D analyst extension

• The 3D Analyst extension is the three-dimensional
  visualization and analysis extension to ArcGIS.
• 3D Analyst adds a specialized 3D viewing
  application, called ArcScene, to your desktop
• It also extends ArcCatalog and ArcMap so that
  you can effectively manage your 3D data, do 3D
  analysis, and edit 3D features.

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Creating 3D features using the 3D analyst
extension

• Deriving the heights of existing features using
  the surface as a reference
• Deriving the heights of existing features using
  an attribute
• Creating 3D features by digitizing over a surface
• Creating 3D graphics by digitizing over a surface

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Deriving the heights of existing features using
the surface as a reference

• Add the 2D features and the surface to a map or
  scene.
• Click 3D Analyst, point to Convert, and click
  Features to 3D.
• Click the Input Features dropdown arrow and click
  the features that you want to convert to 3D.
• Click the Raster or TIN Surface button to set the
  source for the features heights.

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Deriving the heights of existing features using
the surface as a reference

• 5. Click the dropdown arrow and click the surface
  that you wish to use.
• 6. Optionally, browse to the location where you
  want to save the output feature class or
  shapefile.
• 7. Type the name of the output 3D feature class
  or shapefile.
• 8. Click OK.

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Deriving the heights of existing features using
an attribute

• Add the 2D features to a map or scene.
• Click 3D Analyst, point to Convert, and click
  Features to 3D.
• Click the Input Features dropdown arrow and click
  the features that you want to convert to 3D.
• Click the Input Feature Attribute button to set
  the source for the features heights.

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Deriving the heights of existing features using
an attribute

• 5. Click the Attribute that you wish to use for
  the features heights.
• 6. Optionally, browse to the location where you
  want to save the output feature class or
  shapefile.
• 7. Type the name of the output 3D feature class
  or shapefile.
• 8. Click OK.

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Creating 3D features by digitizing over a surface

• Add the 3D feature class (an existing feature
  class with one of the following geometries
  pointZ, polylineZ, polygonZ) to which you want to
  add features to the map.
• Add the surface that you want to use as the
  source for the features' height to the map.
• On the Editor toolbar, click Editor and click
  Start Editing.

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Creating 3D features by digitizing over a surface

• 4. If you have more than one feature class on the
  map, identify the workspace of the feature class
  in which you will be creating new 3D features.
  Click OK.
• 5. Click the Interpolate Point, Interpolate line,
  or Interpolate polygon button (depending on the
  geometry of the features class you are creating).
  

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Creating 3D features by digitizing over a surface

• 6. Create the edit sketch for the feature just as
  you would for a 2D feature.
• 7. When you are finished digitizing, click Editor
  and click Save Edits.
• 8. Click Editor and click Stop Editing.

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Creating 3D graphics by digitizing over a surface

• Add the surface that you want to use as the
  source for the graphics height to the map.
• Click the Interpolate Point, Interpolate line, or
  Interpolate polygon button (depending on the
  geometry of the graphics you are creating).

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Creating 3D graphics by digitizing over a surface

• 3. Click the surface at the location where you
  want to start drawing. If you are using the
  Interpolate Point tool, a point will appear.If
  you are using the Interpolate Line or Interpolate
  Polygon tools, the first vertex will appear.
  Click the surface where you want to create the
  next vertex.
• 4. Double-click the surface to create the last
  vertex and finish drawing.

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Demonstration of creating 3D data in ArcScene
using the Charlottesville DEM

• Open ArcScene
• Turn on the 3D analyst extension by going to
  Tools, selecting extensions, and putting a check
  mark in the box corresponding to 3D analyst

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Demonstration contd

• Add the DEM
• The picture on the right is what it looks like in
  two dimensional form

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Demonstration contd

• Next, right click on the name of the layer and go
  to properties
• Select the base heights tab
• Select the obtain heights for layer from surface
  option button
• In order to make the topography of
  Charlottesville more noticeable, make the z unit
  conversion 5. This multiplies the slope of the
  data by 5

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Adding contour lines to the data

• Select the create contours button on the top
  toolbar
• Click on any point and a contour line will be
  added at that elevation

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Creating 3D layers by obtaining heights from the
DEM

• Add a 2D layer, for example, Albemarle county
  roads
• As you can see, these layers are completely
  independent of one another. However, you can use
  the elevation data associated with the DEM to
  give corresponding heights to the roads

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contd

• Again, right click on the name of the layer (in
  this case tgr515003lkA) and click on properties
• Select the base heights tab
• Make sure all the settings are the same as before

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3D analyst surface analysis options

• The hillshade function obtains the hypothetical
  illumination of a surface by determining
  illumination values for each cell in an elevation
  grid.

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New layerHillshade of cvilleedem
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3D analyst surface analysis options

• Viewshed, another 3D analyst surface analysis
  option, allows you to determine visibility on a
  surface from point to point along a given line of
  sight, or across the entire surface
• The contour function allows the user to add
  contours to the map at specified intervals
• Slope and aspect, as well as area and volume
  calculations are options as well.

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Uses for topographic data

• modeling climate
• water runoff
• minimum safe aircraft flight altitudes
• vacation planning
• topographic data are often used in preparing
  visualization tools such as perspective or
  stereoscopic views of terrain.

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Sources

• http//www.ngdc.noaa.gov/seg/topo/state.shtml
• http//edcdaac.usgs.gov/gtopo30/gtopo30.html
• http//www.nrm.qld.gov.au/property/mapping/topogra
  phic_maps.html
• http//www.dmtispatial.com/canadian_digital.html
• http//mac.usgs.gov/isb/pubs/booklets/symbols/
• ArcGIS Desktop Help
• Getting to Know ArcView GIS

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Questions?