The Maps Made Easy Data Collection Guidelines have a few different clauses to help users avoid collecting data in which the position of the sun itself is affecting the system's ability to match features and successfully reconstruct a scene.
- Avoid Aircraft Shadow Within Camera FOV - If the shadow of the aircraft can be seen in the images that means there will be a hotspot (travelling sunspot) in the images. This moving hotspot will cause processing to fail since the features will appear differently between successive images.
- Avoid Solar Noon - See Aircraft Shadow above. Mapping 1.5-2 hours off of solar noon for your location will keep the sunspot out of your images. Solar noon is acceptable on overcast days as long as there is no shadow.
The main goal of these is to keep the shadow of the these is to keep a strong sun hotspot out of the imagery. The presence of this hotspot essentially changes how the features look to the system between adjacent looks at them. This can result in poor elevation results or even failure to process at all.
We understand that it isn't always possible to avoid these times of day. The best ways to mitigate getting sun spots are to map during overcast periods or use a circular polarizing filter to block the back reflection.
Here is a Flat Map example of what a sun hotspot looks like to our system. Notice that each image has a bright spot in the northwestern corner. This dataset was recorded between 11:11 am and 11:45 am on a day which solar noon was 12:50 pm. *within 1.5-2 hours of solar noon.