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

AdvancedGIS

UsingESRI ArcGIS 9.3

3D AnalystT I N

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”

3D AnalystElevation data

3D models are calculated basing upon appropriate source data.

Basically, contours and elevation point are used.

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)

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

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)

3D AnalystCreate TIN

First of all, a TIN is to be created


For the first TIN, use only Elevation points

Check in the list of layers the proper one


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


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


Triangulate as

Method to be adopted for the interpolations.

Points can only be used as “mass points”


Triangulate as

Lines allow three methods:

“mass points”

“hard line”

“soft line”

Generally, it is better to use the “soft line” method


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


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”


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”


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


Result

Of course, the result obtained using only elevation points will be very rough.

Therefore, it is better to add at least the contours


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

3D AnalystAdd Features to TIN

It is possible either to upgrade the source TIN or to create a new one

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

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”.

3D AnalystTIN

Result

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”

3D AnalystTIN

Representation

Result

3D AnalystTIN

Representation

Use a suitable color ramp (create it, if needed) and use a very small “Defined interval” (e.g. 1)

3D AnalystTIN

Result

3D AnalystTIN

Errors

The interpolation procedure almost always determines errors, such as flat tops and stepwise ridges and valleys

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

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

3D AnalystTIN

Refinement

Result

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.

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

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).

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

3D AnalystTIN

Refinement

Correction Lines

Once drawn the line, it has to be edited to assign its proper elevation to each node.

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

Documents

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