Poor model shape usually results from one or more points that have been incorrectly located by PhotoModeler in 3D space. First, refer to the section of the Quick Start Guide called Guide For Taking Photos. Study the troubleshooting procedure in the above section When processing fails or 3D results look bad for further ideas.
Points that are improperly or inaccurately placed can be the result of:
• The point has one more incorrect references.
• The point has been marked inaccurately in one or more photographs.
• The point has been marked on only two photographs.
• The point has a poor angle maximum (lower than 10 degrees).
• There are too many points which are imaged on just two or three photographs.
• There are sets of photographs that share many points between themselves but share few points with other sets of photographs in the project.
The following lists how you can determine if any of these are the problem and how to fix them:
• To determine if a point is incorrectly referenced, find one marked version of the point on a photograph, select it and choose "Point Audit Selected" from the Review Tab‘s Audit drop down menu).. Review where the point shows up on all photographs. If it is incorrect, fix it by unreferencing it and then referencing it correctly.
• Review all marking on all photographs of the questionable point. Zoom in and make sure the point has been marked correctly.
• If a point is marked on only two photographs (which you would have determined in step 1 above) it will not be as accurate as if it were marked in three of more. Try to find the same physical point in other photographs in the project to mark and reference it there or add more photographs to the project and mark all visible points on the new photographs.
• Point Audit will show you if the point in question has a low angle maximum (i.e. the rays of light from the point to the images it appears on are too close together to get an accurate position in 3D). To fix this, the point must be marked and referenced on another photograph that is from a quite different view than the current photographs it is marked on.
• The Audit Dialog shows how many points have only two rays. If there are too many of these (over half the total points) then overall the model could be quite inaccurate. Try to add photographs to the project so more points are marked on three or more photographs.
• A careful review of the project through point audit will show if there are groups of photographs that share common points but do not share many of these points with other photographs in the project. When some photographs share few points with other photographs in the project, they become disassociated and form a little model unto themselves. In other words, the points shared by the set of photographs could be quite accurate internally but might be in the wrong location or orientation relative to other parts of the complete 3D model.
Ensure that there are no weak links with too few points among sets of photographs. For example, if we photographed a long building with the following set up:
Plan view of a poor camera layout
The two ends of the building at A and B might be accurately measured but might not sit correctly relative to each other because only a few points are shared between the cameras at the A end and the cameras at the B end. If the points shared between the two ends appear on only two photographs, the A and B ends might still not sit correctly relative to each other. In this case, more Camera Stations need to be added along the edge of the building to better tie the two ends together.
Note: Sometimes an object that you expected to be square may in fact not be square. We are used to seeing perfectly square and accurate models created by CAD programs and we are disconcerted when we see a real world object represented by CAD. A model with a bad shape may have some of the problems discussed above or the bad shape just might be the object's true shape.