Advanced GIS Using ESRI ArcGIS 9.3 3D Analyst T I N.

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    22-Dec-2015

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  • Slide 1
  • Advanced GIS Using ESRI ArcGIS 9.3 3D Analyst T I N
  • Slide 2
  • 3D Analyst Activation Be sure to have activated the 3D Analyst extension and load the toolbar. Open the project Base 3 located in the folder Data 3
  • Slide 3
  • 3D Analyst Elevation data 3D models are calculated basing upon appropriate source data. Basically, contours and elevation point are used.
  • Slide 4
  • 3D Analyst Elevation 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)
  • Slide 5
  • 3D Analyst Mask Always be sure to have base layers an area significantly larger than the analysis mask. Otherwise, severe errors will occur along the borders
  • Slide 6
  • 3D Analyst TIN 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)
  • Slide 7
  • 3D Analyst Create TIN First of all, a TIN is to be created
  • Slide 8
  • 3D Analyst Create TIN For the first TIN, use only Elevation points Check in the list of layers the proper one
  • Slide 9
  • 3D Analyst Create 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
  • Slide 10
  • 3D Analyst Create 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
  • Slide 11
  • 3D Analyst Create TIN Triangulate as Method to be adopted for the interpolations. Points can only be used as mass points
  • Slide 12
  • 3D Analyst Create TIN Triangulate as Lines allow three methods: mass points hard line soft line Generally, it is better to use the soft line method
  • Slide 13
  • 3D Analyst Create 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 26 37
  • Slide 14
  • 3D Analyst Create 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
  • Slide 15
  • 3D Analyst Create 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 account Similar to replace
  • Slide 16
  • 3D Analyst Create 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
  • Slide 17
  • 3D Analyst Create 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
  • Slide 18
  • 3D Analyst Create 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
  • Slide 19
  • 3D Analyst Add Features to TIN It is possible either to upgrade the source TIN or to create a new one
  • Slide 20
  • 3D Analyst TIN 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
  • Slide 21
  • 3D Analyst TIN 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.
  • Slide 22
  • 3D Analyst TIN Result
  • Slide 23
  • 3D Analyst TIN 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
  • Slide 24
  • 3D Analyst TIN Representation Result
  • Slide 25
  • 3D Analyst TIN Representation Use a suitable color ramp (create it, if needed) and use a very small Defined interval (e.g. 1)
  • Slide 26
  • 3D Analyst TIN Result
  • Slide 27
  • 3D Analyst TIN Errors The interpolation procedure almost always determines errors, such as flat tops and stepwise ridges and valleys
  • Slide 28
  • 3D Analyst TIN Refinement It is possible to ameliorate the result including further vector data sources, such as those representing the hydrography or the transportation network
  • Slide 29
  • 3D Analyst TIN 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
  • Slide 30
  • 3D Analyst TIN Refinement Result
  • Slide 31
  • 3D Analyst TIN 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.
  • Slide 32
  • 3D Analyst TIN 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
  • Slide 33
  • 3D Analyst TIN Refinement Correction Points Smaller errors can be corrected adding a new elevation point. The elevation can be desumed by the contours (faster if labeled).
  • Slide 34
  • 3D Analyst TIN 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
  • Slide 35
  • 3D Analyst TIN Refinement Correction Lines Once drawn the line, it has to be edited to assign its proper elevation to each node.
  • Slide 36
  • 3D Analyst TIN 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

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