3-D Analysis

NRM 435 Spring 2015
ArcGIS 3D Analyst
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3D Analyst Extension
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The 3D Analyst extension extends ArcGIS to support surface modeling and 3dimensional visualization.
3D Shape Files
Analogous to measures stored in PointM or PolylineM shapes, elevation or depths can
be stored as an invisible Z measure for every point that makes up a point, line, or
polygon theme.
There are 2 basic ways to convert 2D features to 3D features.
1) By deriving feature elevation from a constant value or attribute value.
http://dverbyla.net/nrm435/
NRM 435 Spring 2015
ArcGIS 3D Analyst
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2) By interpolating feature elevation from an elevation surface…
Sometimes you want see what the depth or elevation is within a the pointZ, lineZ or
polygonZ feature.
http://dverbyla.net/nrm435/
NRM 435 Spring 2015
ArcGIS 3D Analyst
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Triangulated Irregular Networks (TINs)
A surface is either represented by an elevation grid or a Triangulated Irregular
Network (TIN). A TIN is a network of triangles with each triangle having a slope
gradient and direction. You can generate a TIN from a an elevation grid, point, line
or polygon themes or 3-D shape files
TINs have several advantages over elevation grids:
1) The surface model is more efficient and accurate because large triangles are
produced for areas that have little terrain variation while many small triangles are
produced to represent areas with high terrain variation.
For example, take a LIDAR raster and convert it to a TIN…
Hillshade produced from elevation raster
http://dverbyla.net/nrm435/
NRM 435 Spring 2015
ArcGIS 3D Analyst
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TIN produced from elevation raster
One advantage ot TINs is relatively small file size compared to rasters:
So in this example, the TIN is 73728/1980176 = 3.7 percent the size of the
raster
TIN Breaklines
Breaks in terrain can be modeled by using point, line or polygon themes as
breaklines.
A hard breakline is where there is a sudden change in slope….examples might be
a line theme of ridge roads, a line theme of streams, a polygon theme of lake
shorelines, etc.
http://dverbyla.net/nrm435/
NRM 435 Spring 2015
ArcGIS 3D Analyst
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Example TIN created using elevation raster and hard breaklines.
Soft breaklines allow you to add edges to a TIN to capture linear features that do
not alter the local slope of a surface. Study area boundaries could be included in a
TIN as soft breaklines to capture their position without affecting the shape of the
surface
Other options for inputs when creating TINs include:
Mass point - individual points are entered into the triangulation process as nodes to
the triangulation. Examples include elevation estimates from GPS stations, contour
lines, or marine soundings.
Clip polygons define a boundary for interpolation. Input data that falls outside the
clip polygon are excluded from the interpolation and analysis operations.
Erase polygons are the opposite of clip polygons. All areas inside the polygon are
marked as being outside the zone of interpolation. Analytic operations such as
volume calculation, contouring, and interpolation will ignore these areas.
Replace polygons set the boundary and all interior heights to the same value.
Examples of replace polygons are lakes and ponds where the water level is a
constant elevation.
Fill polygons assign an integer attribute value to all triangles that fall within the fill
polygon. The surface height is unaffected, and no clipping or erasing takes place.
Once you have a TIN, you can do the following surface modeling operations:
 Add point, line, or polygon features to modify the TIN
 Create contours
 Estimate slope aspect, gradient
 Create a hillshade
 Create a viewshed
http://dverbyla.net/nrm435/
NRM 435 Spring 2015
ArcGIS 3D Analyst
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 Estimate areas and volume
For example, what is the area above 870 meters elevation for the Murphy Dome
area?

Cut/Fill Analysis Cut-and-fill analysis determines how much material has
been lost or gained in a study area by comparing two surface models of the
area -- one before a change and one after. Therefore you need either two
elevation grids or two TINs that represent the surface before and after a cut
or fill
http://dverbyla.net/nrm435/
NRM 435 Spring 2015
ArcGIS 3D Analyst
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ArcScene 3D Visualization
In ArcGIS, ArcScene allows you to create 3-dimensional perspective views.
You can drape point, line, polygon, grid, or image themes over a terrain model
developed from an elevation grid or TIN. Here is an example of a the airphoto
draped over the TIN.
Here is an example, using the themes from the LIDAR lab. First create add your
themes to your viewer…then assign the canopy elevation values to each theme…
Since the X,Y units are in meters and the canopy units are in cm, assign a conversion
factor of 100 so that the X,Y, Z values are all the same units.
http://dverbyla.net/nrm435/
NRM 435 Spring 2015
ArcGIS 3D Analyst
You can exaggerate the vertical dimension of your view.
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NRM 435 Spring 2015
ArcGIS 3D Analyst
You can float point, lines or polygon themes above a surface.
And you can extrude polygons above a surface….
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