To generate an orthophoto, a projection plane must be defined. The projection plane will normally be parallel to the plane(s) of the object being viewed but that is not a requirement. Scale measurements taken from the resulting orthophoto will be valid only for those surfaces that are parallel to the projection plane.
There are two ways to define the projection plane. The first is from the coordinate system. One can choose a projection plane parallel to the XY, XZ or YZ planes. These are given the more understandable names of Top, Front and Right. In PhotoModeler the convention is that Z is height so that is why the top view of an object looks down on the XY plane. This option makes most sense when the project has a Scale/Rotate defined or has been done with known control points. See Importing and Setting Up Coordinate Systems. Note that when geographic information export is requested, the only projection option is Top XY (i.e. looking down at the ground).
The other option for defining the projection plane is to choose three Object Points or Edge Points. Three points will define a plane and the projection plane for the orthophoto can be thought of as being parallel to this plane. The three points are defined by entering in the point ID numbers (turn on Point ID display in one of the Visibility Settings controls to see them). A short cut is provided - if three points are selected before this dialog is opened, they are automatically placed in the three edit boxes.
When an edge is chosen the point displayed will have an ‘a’ or a ‘b’ appended. So 14a means the first point of edge with ID 14. Object Points and Edge Points can be mixed. So the three edit boxes might contain: 12, 14a, 14b which means that the projection plane is defined by Object Point 12 and both end points of Edge 14.
Defining the projection plane alone is not enough to produce the desired orthophoto in most cases. You also need to define the view direction, and what will be the horizontal and vertical axes of the image.
If one of the coordinate planes is chosen, the view direction is defined by one of the two types is chosen. For example, the XY plane has both a Top and Bottom option. Top means the orthophoto is created as a view looking down at the XY plane and Bottom means the orthophoto is created as a view looking up at the underneath side of the XY plane. Having this choice is important especially when modeling a solid object and using the “all photo-textured surfaces” option. In addition there is a rotation control which defines which way the orthophoto is oriented. The angles are in degrees clockwise. Use the preview as discussed below to ensure the result will be oriented as you wish.