Wednesday, March 7, 2012

Interactive Terrain Shaping - Understanding Elements

To begin looking deeper into ITS, I'm going to do the opposite of what the documentation says - I'm going to focus on the right end of the ribbon tab, which deals with elements.  I'll build a simple building pad using elements.

  1. I'll begin with a drawing that has an existing ground surface, a large rectangular polyline, and a small rectangular feature line that represents the top of a building pad.  The elevations of the feature line do not matter.  I have two views: plan view on the left with a 2D Wireframe visual style and 3D on the right with a Conceptual visual style.
  2. Using the Work Canvas command and a rectangular polyline, I'll use the surface to create a work canvas.  I'll also change the style of the existing ground surface to _No Display so that it doesn't get in the way visually.  Here are the steps:
    1. Click Work Canvas on the ITS ribbon.
    2. Select the boundary
    3. Select the surface
    4. Click the surface, then use the Surface Properties command to set the style to _No Display or something equivalent.
  3. If the drawing seems slow, click the grid, then click Spacing on the ITS ribbon.  Click a point in the drawing then enter 10 to make a 10-foot spacing (or whatever number you want to try).
  4. Next I'll use the Add Bounded Flat Plan command to turn the rectangular feature line into a flat planar working grid.  Here are the steps:
    1. Click Create Bounded Flat Plane on the ITS ribbon
    2. Select the grid
    3. Select the feature line
    4. Pick a point near the center of the feature line when prompted for the key point.  This will set the elevation of your feature line to match the surface elevation of the point you've selected.
    5. You might be able see just a little bit of your new grid here and there in 3D view.  Using your CTRL key, click the new grid in 3D view until the entire thing is shown and the working canvas (EG at this point) is hidden.

      What you've created is a working grid.  It has not been added to the finished grid.  If you use your CTRL key and click in a spot where all the grids overlap, you will see this bounded flat grid and the working canvas grid.
    6. Hover over the blue circle at the center of the plane.  When the origin arrows show up, click the z-axis arrow and drag upward.  While holding the mouse button down, type 50 and press Enter to raise the plane 50 feet (or use whatever number you want.  I'm using 50 to make it obvious and more dramatic).
  5. Next, I'll make a fill grid that projects from the edges of the bounded flat plane.  Here are the steps:
    1. Click the Create Fill Grid command on the ITS ribbon.
    2. Select the feature line
    3. Pick a point outside the feature line to indicate the grading side
    4. When you're prompted to select the infill grid, use your CTRL key to select the bounded flat grid in 3D view.
    5. Enter a value in the Grading dialog box for fill slope.  I'm using 33.33 percent in my example, a 3:1 slope.
    6. After clicking OK, you should get a new grid.  Color will vary.  You may also get a warning message about associated objects.  I've been clicking OK and ignoring it.  Not sure what it is yet. UPDATE - More information on this error message can be found here.

      You have created another working grid which is made up of a 3:1 slope projected downward from the edge of the bounded flat grid out to the edge of the work canvas.  Civil 3D has automatically made another grid by combining your bounded flat plane with this fill grid.  Nothing has been added to the finished grid.  If you use your CTRL key and click where all the grids overlap, you'll see four separate grids now: the bounded flat plane, the fill grid, the composite of the fill grid and bounded flat plane, and the finished grid (which is the same as the original work canvas since nothing has been added to it.)
  6. The final step is to combine the fill grid with the finished grid to update the finished grid.  Right now, the finished grid is the same as the original work canvas because no changes have been made.  Here are the steps:
    1. Click the Top Envelope command on the ITS ribbon.
    2. Use the CTRL key to select the fill grid. (think of this as grid 1 for the explanation below)
    3. Use the CTRL key to select the work canvas. (think of this as grid 2 for the explanation below)
    4. After the command is complete, use the CTRL key to find the new composite grid.

      The Top Envelope command pastes the two grids together by keeping everything of grid 1 that is above grid 2 and everything of grid 2 that is above grid 1.
  7. To test it out, click the grid, then click the Grid Surface command.  It will create a surface named "<No Name Provided>".  Assign a style that shows contours and check out the results.

    In the image above, I put the grading grid on its own layer and froze it.  Then I did a REGEN.
Does your head hurt?  Good, that means it's working.  Take a few aspirin, wait 30 minutes, and read this again.  Then try it for yourself!

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