2020 | 025 – Site Modeling – Building the Terrain Mesh from a DWG

By Menchu Cabreros

Apr 25
Topic Progress:

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ARCHICAD Training Lesson Outline

Building the Terrain Mesh from a DWG

RECOMMENDED WORKFLOW FOR SITE DRAWING IMPORT 

A common method of receiving survey data is via 2D DWG showing boundaries and topographic contour lines.

Generally, it is best to place the DWG file in an independent worksheet using the File menu > External Content > Place External Drawing command. The measurement unit is commonly set as 1 foot or 1 meter to correspond to the survey. After import, check a known distance on the site to verify that it is scaled correctly; if it is not, calculate the proportion or percentage from measured to actual distance, then Undo and Reimport with a reworked measurement unit.

Before placing the Survey drawing, set the scale factor of the Worksheet to match the expected output scale, such as 1" = 20'-0" or 1:200. This will usually ensure that the text annotation is in a proper relation and size in the context of the drawing. If you don't know the scale beforehand, use your best guess, then check after import to see if it is noted on the drawing, or to see how the drawing will fit onto your layout sheets; if necessary, Undo, change the scale factor, then reimport.

TIP: Measured distances in DWG files are controlled by the Measurement Unit, while PDF drawing linework will measure correctly based on matching the Worksheet scale to the original drawing scale. 

After successfully importing and verifying the measurements, Save the Current View in the View Map with that scale factor, or adjust the View Settings if the Worksheet already exists in the View Map.

PREPARATIONS FOR SITE TERRAIN MODELING

  • Set Project Location to determine Elevation of Project 0
  • Set North direction
  • Create New Independent Worksheet and set Scale for placing Drawing on Layout
  • Place DWG into Worksheet using File menu > External Content > Place External Drawing
  • Verify dimensional accuracy by measuring a known distance; reimport with different measurement unit if necessary
  • Determine the optimum scale factor so the drawing will fit on a layout properly; if different than what was set originally, you may undo, change the scale factor, then reimport
  • Switch to the Plan view - usually the ground floor story (this allows the site and ground floor walls to be used in conjunction with each other for modeling and site plans).
  • Show the survey worksheet as a Trace Reference
  • Inspect Survey DWG to determine lowest elevation of site model
  • Set Mesh reference level to just below that elevation to minimize thickness

DRAWING THE ACTUAL TERRAIN MESH

  • Draw or trace Mesh on appropriate layer using survey as trace reference, snap to either the property lines or the desired boundary of the terrain (going beyond the property to show context).
  • Select the Mesh, and set each node point (one by one using the pet palette option for Z-height) in the outline to the proper elevation. Do not check the box to Apply to All, so each point elevation is independent. TIP: Switch to Sea Level reference to make it easy to coordinate with survey annotation.
  • To add contour lines, with the Mesh selected AND the Mesh Tool active in the toolbox, click inside the Mesh to define the sequence of points along that topographic contour. Click an extra time on the final point to complete input. Accept the default option to match to user ridges, and the new polyline will then ride along the existing surface elevations.
  • With the mesh selected and mesh tool active, press down on one of the points on that contour line and use the Z-height option in the pet palette. Choose the correct elevation for that contour (choose Sea Level reference from the popup) and check the box to Apply to All (which will affect all points in that polyline).

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