advanced gis using esri arcgis 9.3 3d analyst t i n
TRANSCRIPT
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AdvancedGIS
UsingESRI ArcGIS 9.3
3D AnalystT I N
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3D AnalystActivation
Be sure to have activated the 3D Analyst extension and load the toolbar.
Open the project “Base 3” located in the folder “Data 3”
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3D AnalystElevation data
3D models are calculated basing upon appropriate source data.
Basically, contours and elevation point are used.
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3D AnalystElevation data
. For more accurate models, more data can be used (e.g. rivers, roads, scarps etc.).
Almost all data can be extracted from topographic vector maps (Select by Attributes)
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3D AnalystMask
Always be sure to have base layers an area significantly larger than the analysis mask.
Otherwise, severe errors will occur along the borders
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3D AnalystTIN
ArcGIS generates a TIN (Triangular Irregular Network) to interpolate elevation data and create a vector 3D model.
Connecting adjacent elevation points or nodes, triangles oriented in the 3D space are created, thus allowing to have a z for every possible x,y
Other GIS packages interpolate between vector data creating a raster map of elevation (one elevation for each pixel)
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3D AnalystCreate TIN
First of all, a TIN is to be created
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3D AnalystCreate TIN
For the first TIN, use only Elevation points
Check in the list of layers the proper one
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3D AnalystCreate TIN
Height Source
i.e. the location of the values to be used as local elevation.
It may be the Z value for 3D features or any numeric field
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3D AnalystCreate TIN
Height Source
i.e. the location of the values to be used as local elevation.
It may be the Z value for 3D features or any numeric field
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3D AnalystCreate TIN
Triangulate as
Method to be adopted for the interpolations.
Points can only be used as “mass points”
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3D AnalystCreate TIN
Triangulate as
Lines allow three methods:
“mass points”
“hard line”
“soft line”
Generally, it is better to use the “soft line” method
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3D AnalystCreate TIN
Triangulate as
Lines allow three methods:
“mass points”
“hard line”
“soft line”
Generally, it is better to use the “soft line” method
“mass points”
“hard line”
“soft line”
source data
15
2637
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3D AnalystCreate TIN
Triangulate as
Polygons allow eleven methods:
“mass points”“hard line”“soft line”“hard clip”“soft clip”“hard erase”“soft erase”“hard replace”“soft replace”“hard value fill”“soft value fill”
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3D AnalystCreate TIN
Triangulate as
Polygons allow eleven methods:
“mass points”“hard line”“soft line”“hard clip”“soft clip”“hard erase”“soft erase”“hard replace”“soft replace”“hard value fill”“soft value fill”
same as for lines
Removes everything outside the polygon(s)Calculates the TIN only inside the polygon(s)Removes everything inside the polygon(s)Calculates the TIN only outside the polygon(s)Replaces the TIN with the values calculated only from the polygon(s)As before, but allows the hidden objects to be taken into accountSimilar to “replace”Similar to “replace”
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3D AnalystCreate TIN
Tag value field
An integer value can be stored in the TIN for every triangle and node.
They are typically used to store the accuracy of each elevation
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3D AnalystCreate TIN
Result
Of course, the result obtained using only elevation points will be very rough.
Therefore, it is better to add at least the contours
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3D AnalystCreate TIN
Adding Layers
To add a new layer to the calculation of a TIN it is possible either to create a new one using all the selected layers of to use the “Add Features to TIN” tool, upgrading the esisting TIN
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3D AnalystAdd Features to TIN
It is possible either to upgrade the source TIN or to create a new one
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3D AnalystTIN
The TIN derived from both elevation points and contour lines is much more detailed.
Anyhow, errors will affect the borders; therefore it is much better to include the mask to clip the TIN
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3D AnalystTIN
The mask (polygon!) is to be used as soft clip (i.e. allowing to take into account also the features located outside the clip area).
Obviously, the “Height source” is to be set to “none”.
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3D AnalystTIN
Result
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3D AnalystTIN
Representation
It is generally better to remove the source features from the representation. If needed, is much better to activate the source layer(s).
To do this, deselect the “Edge types”
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3D AnalystTIN
Representation
Result
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3D AnalystTIN
Representation
Use a suitable color ramp (create it, if needed) and use a very small “Defined interval” (e.g. 1)
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3D AnalystTIN
Result
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3D AnalystTIN
Errors
The interpolation procedure almost always determines errors, such as flat tops and stepwise ridges and valleys
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3D AnalystTIN
Refinement
It is possible to ameliorate the result including further vector data sources, such as those representing the hydrography or the transportation network
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3D AnalystTIN
Refinement
Obviously, streams and roads have varying elevations, therefore they have to be stored as 3D lines (one elevation for each node) and the “X value” is to be used for the creation of the TIN
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3D AnalystTIN
Refinement
Result
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3D AnalystTIN
Refinement
Anyhow, some errors will remain.
When an error is due to a wrong value stored as elevation in a feature, obviously it has to be corrected editing the wrong figure.
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3D AnalystTIN
Refinement
Other errors simply are the results of triangles created from three nodes having the same elevation.
To correct them, it is necessary to create new shapefiles (generally, one of points and one of 3D polylines) and use them to introduce new features in order to have a correct interpolation
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3D AnalystTIN
Refinement
Correction Points
Smaller errors can be corrected adding a new elevation point.The elevation can be desumed by the contours (faster if labeled).
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3D AnalystTIN
Refinement
Correction Lines
For larger errors, it is generally better to use 3D lines.
It is generally suggested to activate the snapping to both contours and elevation points
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3D AnalystTIN
Refinement
Correction Lines
Once drawn the line, it has to be edited to assign its proper elevation to each node.
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3D AnalystTIN
Refinement
Correction
Result
This procedure is to be repeated until a good result is achieved.
Remember to close the editor before starting the creation of a new TIN