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Create Bridge Terrain Model

This page describes the steps for creating a bridge structure terrain model from MX data to be used in OpenRoads. The directions in Create Terrain Drawing Features - Introduction should have been followed, prior to preforming these steps.

Important: Skip this page if there are no Bridge Structures on this project.

Refer to the following steps to first import the MX Bridge Structure strings to OpenRoads Features. Then create a Terrain model from these features that will represent the Bridge surface.

Import the Bridge features

  1. Open the Terrain drawing's Default-3D model. From the Terrain Modeling task menu, select the Create From File tool. Select the project's Model.fil and click Open to advance to the Import Terrain Model panel.
  2. From the Import Terrain Models panel, check the TOPO STRUCTURE model. Verify that under MX Options the Default Style Sey is set to TOPO.pss. If not exit MX and go to Before Opening MX.
  3. Set the Import Options to Import Features Only and set the Source to NH83/2001F if useing US Survey Feet or leave blank for Feet. Click Import.

rotated bridge deck features

Create a terrain model

  1. Next, Rotate View with the Method set to Dynamic. Look to insure that all the generated features appear to be related to the bridge structure. Use Element Selection to select all of the bridge structure features.
  2. From the Task menu, select Terrain Model > Create From Elements.
  3. create terain model dialog boxRefer to the Create Terrain Model sample panel to the right. Set the Feature Type to Break Lines, the Edge Method to Max Triangle Length, the Max Side Length to 15, the Feature Definition to Existing Boundary, and the Name to the Existing Bridge Name. Data point (left-click) to add the selected elements to the Terrain model and accept each prompt by left-clicking in the graphic area. Reset (right-click) to finish the command.
  4. Select the boundary of the terrain, and view the Element Information. Change the Max Side Length value until the Border is tight around all the bridge deck features.

Repeat, creating terrain models for any other bridges. Save the Terrain DGN.

Any features not part of the bridge can be left in the dgn as the next step is to import the rest of the MX strings as Features.

Text File Format symbol Text File Format (.txt). Visit nh.gov for a list of free .txt readers for a variety of operating systems.


New Hampshire Department of Transportation
PO Box 483  |  7 Hazen Drive  |  
Concord, NH  |  03302-0483
Tel: 603.271.3734  |  Fax: 603.271.3914