Tie point types
TerraPhoto distinguishes between different types of tie points/lines:
•Ground point - a common point seen in multiple images. The software does not know the coordinates of the point but it knows that it is on the ground or very close to the ground elevation. This type is only available for aerial imagery missions.
•Air point - a common point seen in multiple images. The coordinates of the point are not known and it may be off from the ground elevation.
•Known xyz point - the easting, northing, and elevation coordinates of the point are known. The point is visible in one or multiple images.
•Known xy point - easting and northing coordinates of the point are known. The point is visible in one or multiple images. This type is only available for aerial imagery missions.
•Depth point - a point seen in multiple images. The software does not know the coordinates of the point but it knows the depth from the camera position to the tie point. This type is only available for mobile imagery missions.
•Known depth point - the coordinates of the point and the depth from the camera position to the tie point are known. The point is visible in one or multiple images. This type is only available for mobile imagery missions.
•Line - a common line seen in multiple images. The software does no know the exact position of the start and end points of the line but it knows that it is on the ground or very close to the ground location. A perpendicular correction to each line is calculated.
•Known line - the easting and northing coordinates of one point along the line are known and the line is located on ground elevation. The line is visible in one or multiple images. A perpendicular correction to each line is calculated.
•Straight line - a line that represents a straight linear feature in an image of a mobile side-looking camera. This type is only available for mobile imagery missions.
The availability of tie point types depend on the system that captured the data: airborne or mobile ground-based system.
Ground tie points are typically the most common type of tie point used in TerraPhoto workflow for aerial orthorectification projects. Air tie points are most often used to improve the internal positioning of mobile imagery. Depth and Known depth tie points can be utilized for deriving TerraMatch correction values for trajectory drifts of mobile system projects. Straight lines are used for calibrating the lens distortion of mobile side-looking images.
