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TerraBuilder allows you to define the geographical coordinates of a layer with respect to the coordinates of other reference layers. This allows you to view a layer, whose coordinates are unknown, and to set its coordinates by inserting a number of tie points in both this layer and the layers with known coordinates. Each tie point appears in both layers, and represents identical physical features.
For example, you can adjust the coordinates of an Elevation Map file based on an Image Map file with known coordinates. You view the two files, side by side, in the Reference Layout mode and insert tie points at points that appear to represent the same physical feature (hill tops, road junctions, coastline etc.).
- If you insert one tie point (in each window), and you know the UPP for the layer in the Working Window, TerraBuilder calculates the geographical coordinates for the layer.
- If you insert two tie points (in each window), TerraBuilder calculates the scale factor and applies it to the layer in the Working Window, thus providing both geographical coordinates and UPP (in X and Y axis) for this file. You should insert two tie points if you can identify the features in the two views with sufficient precision.
- If you insert three tie points, or more (in each window), TerraBuilder calculates the average scale factor. You should insert three, or more, tie points if it is difficult to identify the features with precision.
Placing, Moving, and Deleting Tie Points
For the best results, place the tie points at points that appear to represent the same physical feature, such as distinct landmarks, road junctions, coastlines, etc.
To place tie points:
- In the Layer List, select Edit mode for the layer whose UPP and coordinates you want to adjust.
- In the Layer List, select Reference mode for a reference layer with a known UPP and Coordinates.
- On the Tools tab, in the Tie Points group, click Place Tie Points. The Place Tie Points command is only enabled when a single layer is selected for edit and at least one layer is selected for reference.
- In one of the windows, click to place the tie point. The new tie point is red and numbered.
- In the other window, click to place the corresponding tie point. The new tie point is red and has the same identification number.
To move a tie point, place the cursor on it until it changes it to a four-arrow cross cursor, and then click and drag the tie point to the new location.
To delete a pair of tie points, right-click a tie point and select Delete Tie Point.
- Repeat Steps 4 and 5 to add as many tie points as required. When a new tie point is placed, the previous tie point turns green.
Adjusting a Layer Using Tie Points
To adjust a layer’s dimensions based on tie points:
- Place the tie points.
- On the Tools tab, in the Tie Points group, click Adjust Layer.
- If a tie point in the Working Window has no corresponding point in the Reference Window, an error message is displayed. Click OK to ignore this point and use the remaining points, or Cancel to add the missing tie point.
- Check the adjustment: click the Windows Lock button in one of the windows to link the windows, and use the Superimpose Windows slider to check the accuracy of the adjustment. You can move or remove existing tie points to fine-tune the adjustment.
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