Workshop Notes
23 September 2003
Digital Terrain Modeling

NOTE ON HOMEWORK SUBMISSIONS:
Save your work for assignments to the classes directory: G:\Arch541\submit\yourworkshoptime\yourTA\your folder
Only you, your TA, and your professors can access this folder.

------- Digital Terrain Modeling --------
Mechanisms for generating terrain, landform, landscapes, etc.
We will look at two of the available three.
1. Bentley Architecture (built-in tools)
2. Geopak
3. InRoads

Getting Started:
-Copy the .dtm folder from the classes folder to your :t\ drive for the exercises to follow.
-See notes on class website (handouts) for Digital Terrain Modeling. This document details the steps to reference a contour map into MicroStation to trace contours. (will be updated)
-Create a new Bentley Architecture File
-Work in the TOP view window
-SCALE is crucial for work with digital terrain modeling because we are reconciling plan geometry with heights. Make sure that you can see the GRID.

1. Bentley Architecture (built-in tools)
-Pull out the terrain set of tools. Architecture->Architectural Modeling. This is the first icon at the top left of the Architectural Modeling Palette.
-In View Attributes (menu from the "B" at the top left of your window), turn off the Clip Back, Front, and Volume options, so that you can see what you are drawing. Hit Apply.
-1st tool, Place Contours: set interval for contours (5') and start with a current contour value of 0.
-Draw a contour (curved lines will be drawn). You can close contours if necessary. NEVER cross contours. Contours cannot cross.
-When you finish a contour, select the + key, and you will be ready to draw the next contour. This increments your current elevation upward by the interval value set.
- Continue to do this for several contours.
-You can now use the rotate tool to see your contours drawn at their appropriate elevation.
-Go back to the TOP view.
-The second tool allows you to assign values to contours already drawn at zero elevations.
-The third tool allows you to create a MODEL. You define the cut direction, and the program will create a series of profiles that describe the surface. Depth below lowest point can be changed, depending upon how much volume you want to see below the surface. Distance between cuts defines how close these cuts will be together. The closer they are, the higher the accuracy of the form. Smoothing tolerance is less accurate, but creates smoother surface.
-Draw a rectangle around the contours for which you want to generate a model. The rectangle should be completely outside of the contours. Click to accept, and the model will generate. Render, and see the surface model.
-You can modify the contours (using modify elements tools) and then update the terrain model with the update model tool (last tool in the tool palette, using a rectangle again). The terrain is linked to the contours.
-You can also use Boolean operations and subtract solid objects from the terrain. (a box or sphere, etc.)
-A higher level of complexity can be achieved using Geopak.

2. Geopak
-go back to plan view and switch to level 2.
-We are going to look at a survey from which we will derive our contours.
-Utilities->Image->Display
-Find topo2.jpg on the dtm folder that you copied earlier. This image was scanned in from a paper map that was drawn at a 1'=300' scale. We know that the image size is 7.5 by 12 inches. You can find this information in Photoshop in image size. We know how big the survey is by using scale and size. We must know this information to get the image into Microstation at the proper scale.
-CLOSE the image. We were just viewing it. Now we will bring it in to Microstation.
-Draw a rectangle that is the proper size. Draw in the x-direction. Accudraw is also a calculator. Type in 7.5 (that is inches) now hit the star key (*) and 300 (that is feet). Hit enter, and you have your x dimension. Drag up to the y-axis. Type in 12*300 and enter, and you have the rectangle that is the appropriate size. FIT VIEW. This is the size of the survey. Now we have to bring it in.
-FILE->Raster Manager. FILE->attach. Find the file again. OK. Now we have to tell the program where the image is going. Use a tentative (both mouse buttons at same time) to snap at the bottom left corner of the rectangle. Click to select. "Rubberband" to upper right corner. Snap (tentative) and select. The file will attach to the rectangle at the correct scale.
-You can see image settings in raster manager window. You can select invert to make it white on black. You can also deselect the file to turn it on and off of you do not want to see the image. Close the raster manager.
-Use your terrain tools (same that we used in Part 1). Interval at 20 (figure this out from the survey). Start at 620 (or wherever you like). Draw the contours by tracing those on the survey. You may need to turn Accudraw OFF (toggle icon at top) while tracing or digitizing contours. Draw as many contours as you like. You can check your progress and see their elevations by rotating around.
-Go back into Raster Manager and shut off the image.
-Now we will create a model in a different way. Go to Applications->Geopak
->Activate Geopak. Now go back to Applications->Geopak (and you will now see all of your options) Go to Geopak Site->dtm tools. New Dialog box with palettes will appear.
-Extract Graphics (second down on left). We are going to create databases of information from the contours you have drawn.
-Give it a file name, and tell where you want to save it (files button)
-For now, we will CREATE a new file. Feature is the KIND of information. These relate to parametric design. There are several different kinds. We will use CONTOURS. You could APPEND spot elevations, etc. later to add additional information. Mode is EXTRACTION. Search Criteria: These are filters to choose elements in your drawing. The easiest way to tell the program what to select is by level name and color. (Try to keep contours in their own level and color) Choose names and colors. Choose Match and select one contour in the file. The system will find any elements that are on the same level AND are the same color. The DISPLAY button will highlight all elements that it found. You must use the extract button to extract what is VISIBLE. Choose apply. The database is created.
-Now we must generate the terrain. BUILD TRAINGLES button to the right. Take data file, and convert it into a TIN file. Finds ALL points (clicks that you made) and will draw triangles between all of the points that you made, creating surfaces between the points. Give it a name (site.tin), and hit process.
-Close Build Triangles tool. Find the Eyeglasses (Load DTM Features). This is for viewing the model. Load file. (there are three here: the original .dat file, the .tin file, and the lattice. Set it on TIN. Look through the list of features. The triangles are there and several others. Double click on DISPLAY by triangles to turn them ON. Double click on the line below to change to what level or color you want. Make sure that the Display Only checkbox is NOT checked. Choose the LOAD button at the top right. You should now be able to view your model/terrain by rotating and rendering.
-This is a Triangulated Irregular Network model. It is sometimes difficult to read. You can use a lattice that is easier to read. Go back to Build triangles, and choose lattice. Name the file, and load the lattice file, and turn on the lattice features. This creates a gridded model that is a little more legible.