Using Tie Points

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.