Overlap Reports

As of January 2, 2016 all georeferenced Maps Made Easy jobs will have an overlap report image that is generated at the time of processing. The overlap report is available at the bottom of the Map Detail page.

Overlap Reports can be used to diagnose 95% of issues that users experience when they are unhappy with their outcomes.

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An Overlap Report is in image that shows the user how many images contain a view of any location within the processed survey area. Generally, the more "looks" at an object the system has to work with, the better the outputs will be (within reason). The Overlap Report color codes these numbers to let users know when the system considers to be good or bad overlap coverage and helps them visualize the things that affect the collection of consistent overlap.

1, 2, 3, 4 or 5 views (reds) of an area is considered to be totally inadequate for the purposes of reconstructing a 3D scene. 6, 7 or 8 views (greens) is considered adequate for the reconstruction of fairly simple objects like fields, basic structures or stockpiles. For the greatest ability to reconstruct a complex scene, getting 9 or more views (blues) is required to have the detail necessary to reconstruct complex objects like buildings, trees or other vegetation.

A red dot at an imaging location denotes that there was an image that was processed but it did not have sufficient overlap and/or matchable features so it was not included in the output.

The following examples are provided to help users see how various scenes will affect the achieved overlap. As always, our Map Pilot application for iOS will help to manage the basics but knowing about your survey area's terrain and contents will go a long way towards collection proper data.

Good Overlap

This is an example of good and consistent overlap. There will usually be some red areas around the edges that may not turn out perfectly but everything in the interior of the survey area will turn out very well as it is shaded mostly dark blue and blue.

Overlap Settings

The move overlap you have the less gaps there will be in the dark blue sections of the Overlap Report. A fully dark blue overlap report is a good goal. We generally recommend using 80% overlap as a starting point. 80% is the default value in Map Pilot Pro. 

60% Overlap - 5-8 looks at everything - No blue, might work on the most simple scenes. Maybe.

70% Overlap - 8 to 15 looks at everything - Areas of blue but inconsistent. 

80% Overlap - 18 to 20 looks at everything - Consistent coverage that makes successful maps. 

Bad Overlap

50% overlap is barely enough to work. Consider this the bare minimum. This was taken over a flat and feature rich area with no trees. Any complex features in this survey area got mangled. 

These are example or insufficient and inconsistent overlap that was collected using free flight and the camera intervalometer. Overlap like this will result in bad edges, large gaps, badly distorted imagery and a flat 3D model reconstruction except for in the green and blue areas.

Gaps in Imaging

This shows that the overlap is mostly good but the lack of black dots, which represent the imaging locations, in various areas long the passes will result in poor reconstruction in those areas. Gaps in the imaging interval are caused by loss of line of site when using the Map Pilot app.

Elevation Difference Overlap Reduction in Structures

The structure shown in the colorized DEM above are roughly 17 meters tall. When flying relatively low at 40 m, as was done for this survey, that will correspond to a significant reduction in the overlap achieved on the tops of the structure. Being that the structures were likely the target of the survey, this is not good... This is one of the main causes of the imagery being "swirly" on the tops of structures. This particular example worked out because it was feature rich. Flat roofs will not likely be so lucky.

Elevation Difference Overlap Reduction in Terrain 

The terrain on the right was roughly 50 feet higher than the terrain on the left. For the particular example, the cruising altitude was 130 feet above the starting point, which was about 30 feet below the high point. This resulted in significant overlap loss as the higher terrain crept up closer to the cruising altitude of the aircraft.

Too Much Overlap is Inefficient

While too little overlap will result in sub-par results, having too much overlap is inefficient with our system resources and the user's processing points. There is no evidence that having this much more overlap will help produce higher quality outputs.

Overlap Reports are a great tool for users to learn about the 3D reconstruction process and debug their own data collection processes.