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Tracing Image Features

Updated July 08, 2021

This article applies to:
  • Terrain 3D
  • Terrain Forestry
  • RoadEng Civil
  • RoadEng Forestry
This Knowledge Base article is an excerpt from one of our tutorial files. The files referenced in the article, as well as the full tutorial document, are available in our Tutorial Installer.  

The following steps demonstrate how to trace features in the image and use them to calculate their area. This example continues on from Scaling an Image

  1. Plan | Plan Options button | General tab. Change the scale to 5000 if working in metric units (or 1000 if working in feet units).
  2. Scroll and zoom the Plan window so that the pulp mill buildings are visible as in figure below.

Figure 1: Ocean Falls Buildings

If you have already done the Drawing Features exercise in the Basic Mapping and Drafting chapter above, then you should have no problem with the next step. Otherwise, the sub-steps (a, b, c) should help. chapter above, then you should have no problem with the next step. Otherwise, the sub-steps (a, b, c) should help.

  1. Trace around the boundary of three of the buildings using the mouse (like in the figure below).
    1. Home | Draw New Feature button.
    2. Begin drawing a new feature. Left-click anywhere to create a new point.
    3. Position the cursor over one of the corners of a building and left-click again to anchor the point.
    4. Left-click away from the first point to create another point (note the line joining the new point to the old).
    5. Position the cursor over the next corner and left-click again to anchor the point.
    6. Repeat until only one segment of the building is not outlined.
    7. To join the last segment use Feature Tools | Join.
    8. Click the Draw Feature button to begin a tracing a new building.
    9. When you are finished, use the right-click to change back to select with mouse mode.

Note: The mouse can be used to edit existing points and insert points . Don’t forget about the Undo button or<Ctrl-Z>.

If you have a number pad on your keyboard, there is a digitizing feature you might want to try; move your mouse cursor over a point of interest and type the <5> key on the number pad. This will create a new feature point in one step.

Determine the area of each building:

  1. Select each building perimeter with the mouse and look at the Status portion of the Feature Properties window.

Figure 2: Traced Buildings with Status Details in the Feature Property Panel

  1. Format the perimeter features and then determine the total area:
    1. Select all the traced buildings, by holding down the <Shift> key and left-clicking on each of the building’s traced boundaries.
    2. Feature Tools | Line-types, Symbols button (or type <Ctrl-L>).
    3. Select Line/Border Type: 6-thick (heavy).
    4. Change the color to blue.
    5. Press OK.

View the Feature Properties panel, View | Add to Panel button| Feature Properties from dropdown list. To see the area of the selected features: Area Subtot. If working in metric units, the area of the buildings should be approximately 2.9 Ha. (Imperial units the area should be approximately 7.0 acres).

Figure 3: Selected Buildings with Area Reported in The Status Window

  1. One can add or remove items by pressing the button at the bottom of the feature properties panel. Area Tot. and Area Subtot. can be added to list of selected features.
  2. The total area (Area tot.) includes the bitmap boundary; the Area field shows only the area for the current feature (containing the red cross).

Note: The Status window options allow you to display areas in square meters (square feet) for the current feature. Click outside the image to de-select all.

  1. File | New. Do not save changes.