WMS:TIN Menu

TIN Options

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TIN Options dialog

Merging TINs

You can merge a selected TIN with another TIN using the Merge command in the TIN menu. This is particularly useful if you wish to merge a TIN generated from one program with a TIN derived from a background elevation source such as a DEM.

For example you may have surveyed data with a lot of detail for a part of your project (such as a roadway profile) and wish to combine that with a TIN derived from a DEM of the surrounding area.

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The following dialog is used to select existing TINs for merging. The merged TINs can be completed merged (all vertices combined and retriangulated), or you can specify to have vertices in overlapping regions deleted. You can delete old TINs if you wish, or keep them.

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The following rules are adhered to when merging a list of TINs:

• The TIN at the bottom of the list of TINs to merge has the highest priority, meaning that all of its triangle edges will be preserved while vertices that overlap from TINs higher in the list will be deleted.

• If a region being deleted from one TIN overlaps any stream vertices on the TIN being deleted, the stream will be split. The stream will be cutoff wherever it "enters" the TIN selected for merging and begin again upstream where it "exits."

• Drainage data will be lost and not transferred as part of the merged TIN.

Fill

The Fill command triangulates a selected polygon and merges it with the original TIN. Vertices should be distributed according to the density of TIN vertices desired on the interior of the TIN. The primary purpose is to fill in an area where data is missing on a TIN, or where you wish to retriangulate to a higher density.

You must have some kind of background elevation behind the polygon (e.g. a DEM or another TIN), or the resulting vertices within the polygon will all have zero elevations.

Filter

Redundant and overlapping data may exist in a scattered XYZ data sets. WMS offers the ability to filter the data and remove unnecessary data points in relatively flat areas in the Filter command from the TIN menu. The user specifies an angle. Each data point is checked to see if it is in a flat region by dotting the normals of the surrounding triangles.

If the normals are all within the specified angle, the region is considered flat and the point is deleted.

This type of processing is very important when trying to use LIDAR data. Typical LIDAR collection results in resolutions of 1-3 meters so that good detail of flood plains and channel banks is achieved. However this leaves massive amounts of points in relatively flat areas where the increased resolution is not required (it would be like asking your surveyor to get points every 5 feet just so he doesn't miss anything, when hopefully he can be much smarter). The filtering eliminates the points where they are not needed and retains the important points. (The reference to Creighton Omer's paper is about a study using this technique on LIDAR data for hydraulic modeling that concludes a filter angle of 4-8 degrees can be used that will result in up to 85% data reduction without impacting hydraulic modeling results.)

Trimming TINs

Trimming allows you to eliminate all vertices that are outside of a selected feature polygon. You must first create the feature polygon in the Map module, then select the polygon you wish to use prior to selecting the Trim command from the TIN menu (Terrain Data module).

Correcting Split Flow

Split flow vertices can usually be corrected by finding a channel edge leading into the split flow vertex, and swapping it. This edge swapping can be done automatically using the Correct Split Flow command from the TIN menu of the Drainage module. If the edge cannot be swapped without creating overlapping triangles the split flow vertex will not be eliminated and you will have to add new vertices, adjust elevations, swap multiple edges or some other form of manual editing technique.

TIN Interpolation

Interpolate TIN To TIN

The Interpolate to TIN command of the TIN menu allows you to interpolate the elevations of the active TIN to one or more TINs. If more than one other TIN exists a dialog will appear that lets you select the TIN(s) you wish to interpolate to. No changes occur in the elevations of the active TIN.

Interpolate TIN To 2D Grid

The Interpolate to 2D Grid command of the TIN menu interpolates the elevations of the active TIN to the 2D Grid. Only available if both a TIN and a 2D Grid exist.

Related Topics

• TIN Guidelines
• Triangulating
• Deleting Vertices
• 2D Grids
• Interpolation Options