COMPUTER AIDED ARCHITECTURAL DESIGN
 Workshop 11 Notes, Week of November 17, 2013

 DIGITAL TERRAIN MODELING

Note: This workshop focused on a number of digital terrain modeling methods. The primary method of more immediate practical value is captured under item #2 below as applied to Carr's Hill. The methods described later on  involving external "tin" and "lat" files  are more advanced and relate to analysis options that you might undertake in studio. 

  1. Reading Elevation Data From A Bit Map
    1. Goto File menu and open Raster File Manger and attach the file monalisa.jpg using interactive placement.
       
            2. The image is then placed interactively within the plan view.

           
            3.  Go to the Surface Modeling Task, and select the "Surface by Image" tool.

              

             4. Using the "Surface by Image" tool, select the file "mona-list.jpg"  and with  the "Proportional  to Image" option checked on, enter two data points at the upper left-hand and the upper right hand corner of the image.  The specified "Height" ," U Sample Points" and "V Sample Points" will determine the elevation range and resolution of the resulting surface.

               

           5.  From pull down menu association with the second icon from the upper left hand corner of the view window, render the generated surface with the "Smooth with Shadows" option to see the result.

           

2.  Terrain Modeling  (expeditious method)

       
        dgn file of Carr’s Hill
  1. Open Carr’s Hill.dgn after copying it to your computer from the classes folder.
  2. Rotate to view 3D survey data – typical of GIS data received from municipality
  3. Create and make active a new layer titled "simpleTIN".
  4. Also create layers titled "advanceTIN" and "latticeSurface."
  5. Turn on predefined contour layers named " INDEX" and" INTERMED", and turn off all other layers except for the active layer simpleTIN.


    create levels


    make simpleTIN the active level
  6. Select "Mesh from Contour Tool" from pull out toolbox from icon in lower left-hand side of Surfaces palette.


  7. Select the tool and then hold down continuously the left mouse button to draw an invisible box around the contour lines on the screen. Move the mouse off the contour lines, and hit the left mouse button  to accept the contour lines and generate a triangulated mesh.

[ADVANCED METHODS]

3.   Creating Terrain File Using Geopak

  1. Geopak is loaded into Microstation by choosing Activate BENTLEY CIVIL under the Applications menu if not already done previously.

    ag

  2. The task menus on the left-hand side of the Microstation window will now include a tab for "Geopak Site". Selecting this tab activates the set of menus that most directly relate to the use of Geopak.

         

  3. Note that the prior set of menus can be restored by selecting the  "Tasks" tab (highlighted in green below) that is located just above the "Geopak  Site" tab:


  4. Turn off the layer simpleDTM, and rotate into the top view such that only the contour lines are display (layers INTERMED and INDEX). Make advancedTIN the active layer
  5. From the DTM Tools Tab, Select the "Extract Graphics" tool (Q2):


  6.  The dialog box settings, set File Type to "Binary", File Open to "Create", Feature to "Contours", Mode to "Extraction", and then under Search Criterion, check-on the check boxes for  Lv Names: and Colors, and hit the Reset button so that all the text fields for the search criterion are empty. Use the magnifying glass icon in the upper right hand corner to name a new extraction file such as "site.dat".

  7. Select "Match" button, and using the left mouse button, select one of the topo lines (eg., light gray). Accept the selection by moving the mouse off the topo lines and hitting the left mouse button once again in a area of the drawing without other graphic elements. Repeat the same process for the second set of topo lines (dark gray). The Extraction Graphics dialog box will then be populated with the levels and colors of these two topo lines as follows:

  8. Select the "Display" button  and the full set of elements founds by the Search Criteria will highly in Pink.  The name of the "Display" button will change to "Undisplay".


  9. Select the "Undisplay" button to turn off the highlight on the contours and select the "Apply" button to create the external site.dat file.
  10.  The same file also contains spot elevation data.  Turn on the the level named "SPOT, turn off the contour levels, and reset File Open to "Append" and Feature to " Spots".  Reset the Search Criteria and then use the same Match technique as before to select the spot elevation data.

  11. Select the Apply button to append the site.dat file with the additional SPOT elevation data. Thus, the external site.dat file now is encompassing both contour and spot elevation data.
  12. The next step requires converting the dat file to an external  tin file (triangulated irregular network file). Select the Build Triangles tool and specify the source file "site.dat" and the new file "site.tin" and select the "Build Triangle" button.
     
    select Build Triangles tool
     
    run Build Triangles tool to create site.tin file.
  13.   Similarly choose the "Build Lattice" tool (W3)  to convert the site.tin file to an external  site.lat file (a unform polygonal grid mesh file).

    select Build Lattice tool run tool to convert site.tin to site.lat  file

  14. The external files site.tin and site.lat can now be loaded back into Microstation. Here, choose the Load DTM Feature  tool (A1).  In the load DTM dialog box,  set Load File to "TIN", the file to load to "site.tin", turn on the "Display Only" check-box, turn on the Triangles feature by double-clicking on "Triangles" in the list of features.  Then double click on the horizontal graphic line below the features list to launch the "Set Feature"  dialog box, and designate Level as "advanceTIN" and Color as 11.

    select Load DTM Feature  tool set Tiangles feature type to load onto advanceTIN layer in color 11
  15. Select the  "Load" button in the Load DTM Features tool to temporarily display the TIN model inside Microstation. If this appears to be in good order, then turn off the "Display Only" button and select the "Load" button again to more permanently load the TIN model into Microstation.

  16. Similary, in the Load DTM Features dialog box, the Lattice file can be loaded by changing the Load File type to Lattice, selecting the file "site.lat",  turning on the lattice feature "on", making "latticeSurface"  the active level,  opening the "Set Feature"  dialog box, and designating  the Level as "latticeSurface" and the Color as 11.  This too can be tested with the "Display Only" option first before loading the lattice file into Microstation. 


  17. Note that, using the same method,  the "Contours" feature above can also be loaded into the model to regenerate more normalized contours with major and minor interval lines (see image under part 4, step 10 below).

  18. Once these steps have been performed inside Geopak, a set of analytical tools is available to examine the features for such attributes as slope, drainage, etc. For example,  the "Height/Slope" tool (A2), can be selected to interactively explore the hight slope of the terrain file. Note that you select the external file "site.tin", turn on the check-boxes for showing contour lines, triangles (TIN facets), and flow arrows, and select the "Start" button. Moving the mouse over the drawing window will show slope (blue arrow below), contour lines (white), and TIN triangle (blue), ans well as echo back elevation and slope values numerically as depicted below.
            

4. Terrain from Image File: New CAD File

  1. The Image underlay file topo2.jpg that has been placed in in classes is a scanned in image of a site plan with topological lines. –
  2. Note the scale of topo2.jpg  is 1”=300’ and the actual dimensions of the scanned in image are 7.5 x 12 inches in paper size
  3. Close the image
  4. Inside Microstation, draw rectangle at an appropriate size for attaching  topographic image above,  using the Addudraw popup calculator in the coordinate text boxes for "X" and "Y". After entering a lower left-hand data point, then for the "X" coordinate enter "=" and then "300 * 7.5", and for the "Y"coordinate enter "=" and then "300 * 12.0".


  5. Fit View
  6. Use the File Menu/Raster Manager dialog box, and interactively load the file topo2.jpg and use the "Place Interactively" feature so that it is scaled to the rectangle created in step 4.

  7. Use the Utilities>KeyIn dialog box, to enter "MDL Load Civtools" (tool available for download from School of Architecture website)

  8. Within the Civtools dialog box:
    1. [P] tools – parameters – set major/minor interval and colors/layers

    2. Choose first tool – place contours - establish elevation level for each contour line and trace over the scanned in image using the curve tool option, and setting "planar" check box to on.

    3. Note: you need to explicitly enter in new elevation values into the Place Contour dialog box for each contour line, such as the elevation 580' above.

  9. Set current elevation – 600 – and draw
    Keep going up the mountain.
  10. Once the contours have been created, you may use either Surface tool "Mesh from Contours" tool or the Geopak method to build a terrain file.  (Here is a version of the above file with contour lines (blue) re-loaded and normalized from the external TIN file.

  11. The greatest advantage for the Geopak method comes in the variety of analysis and modification tools now available to explore the generated terrain model. 

    The Drainage tools allow you to see the flow of water on the surface.
    Drainage Patterns tool allows you to visualize the pattern of drainage as it applies to the entire surface.
    The Downstream Trace tpp; calculates the flow of water from a point (anywhere you click on the model) and will show it on the screen as a path.
    The Upstream trace allows you to trace a point (anywhere you click on the model) to where the source of water would be.
    Flow Arrows show you the directinon o water flow accross the entire surface.
  12. The visibility tool gives you line of site between selected observation point  and destination point, and given thematic colors for visible (yellow), not visible (dark gray). The image below at right  depicts the visible area in yellow from an observation point to a target point.


    select Visibility Tool set  display settings  line of sight theme, visible (yellow), not visible (dark gray)



     Additional thematic analysis tools available through Geopak  provide for other types of slope, watershed and cut and fill analysis.  Later this term, we will see how to apply some surfacing tools towards site modification.
  13. Save the file to the Microstation dgn format. Open the dgn file direcly in Rhino. Within Rhino, re-save the file to the 3dm format. Note that Microstation can directly open a 3dm file, but can not save directly to the 3dm format. Simillary, Rhino can directly open a dgn file, but can not save directly to the dgn format.