One of the key elements to merging projects is to ensure they share the same coordinate system and scale. Project Merge will apply a coordinate transformation to all the imported 3D objects in a Project as it is merged into the current "base" project (shown as the top dialog screen capture above)
There are three methods of coordinate transformation:
• No transform: PhotoModeler performs no coordinate transformation when a sub-project has this Transform Type. This method is appropriate if the sub-project (and usually base project also) was done with control points or had a three point Scale/Rotate applied. In this way it is up to the user to ensure the coordinate systems are consistent across the sub projects.
• Translation: PhotoModeler performs no rotation but does translate all the 3D data by the X,Y, Z values specified on the dialog in the Translation Amount area. This method is appropriate if the sub-projects are scaled and rotated using any form of Scale/Rotate (or by Axes Constraints), and they just need to be offset from each other by a known distance.
• Named-Point Match: PhotoModeler performs a match between like-named points, computes the best least-squares coordinate system fit (involving translation, scale and rotation), and applies this transform to the project being merged in. This method is appropriate when there is some overlap between the sub-projects and the sub-projects are not done with control points. Before the projects are loaded they must have at least four 3D Object Points with user applied names (see Object Point Properties).
Note: Any project being merged (base project or other), will have any active Scale/Rotate permanently applied to its coordinates before the merge takes place. This ensures the scale and any desired rotation is consistent before applying other coordinate transforms.
Examples of each of the three transform types in use are:
• No transform: modeling of a factory or process plant where a control point network has been set down by a survey crew and the sub projects are all built around these control points.
• Translation: measuring a long accident scene that has been done in sections to capture different parts of the scene. The sub-projects are all scaled and rotated and the distance along the road between each project was measured at the scene.
• Named-Point Match: a large archaeological dig is being processed by a number of staff. The photographs of each sub-project overlap and there are shared points between sub-projects. These points are named the same in each sub-project. The merge ensures the sub-project fit together optimally at these points.