I need to use my DJI Phantom 4 RTK to fly and photograph the floor of a narrow valley that is fully shaded until about 9am or so. I'll prepare a photogrammetric point cloud using 3DSurvey for image processing. There are tall trees and the shadows are getting rather long these days even at high noon. Overcast days to get photo coverage of shadow areas are infrequent so wondering if, with the P4 camera set to "Cloudy", is there enough light in the shaded valley, before the sun crests the ridge, to get photos bright enough for photogrammetric processing? Anyone experimented with that? Thanks.
Photogrammetric processing of a shaded valley floor
- Thread starter SteveBCH
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Dave Pitman
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The "cloudy" option just affects white balance. For low light, you need a slow shutter speed, and correspondingly, a slow flight speed in order to not have image blur.
adm_geomatics
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I'll add to @Dave Pitman 's great advice in that this would be one of those times appropriate for image editing. I use ACDSee to batch correct image exposure while maintaining the geotags containing the RTK geotags and accuracy properties. I have seen some clouds increase by up to 20% just by regaining detail in harsh shadows and blowout.
AMann
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You could use HDR (high Dynamic Range) processing. It’ll take longer, but do at least two RAW mode (.dng, not .jpg) images (3 would be best) while parked at a dead stop above each photo point. Make one shot with a shorter exposure set for the sunlit areas and a longer exposure one for the shaded areas. Personally, I would even do one more with full area matrix exposure. That way, you brighten up the shadows more by keeping the exposure set correctly for them, and properly exposing for the well lit areas in the same final image.
Do not to change exposures between all the photos in each set though, find what the best exposure is over a well lit area and use that for all of your first set of bright area shots, and then also check for the best exposure over a very dark area and use that for all of the second set of dark area shots. Also, be sure you’re just adjusting the exposure setting for both sets of photos using shutter speed only and the aperture is locked. Funny things happen, like different levels of depth of field, between images when you change aperture.
Several processing programs, including Photoshop can work with HDR imagery to blend them together into one uniformally exposed image.
Do not to change exposures between all the photos in each set though, find what the best exposure is over a well lit area and use that for all of your first set of bright area shots, and then also check for the best exposure over a very dark area and use that for all of the second set of dark area shots. Also, be sure you’re just adjusting the exposure setting for both sets of photos using shutter speed only and the aperture is locked. Funny things happen, like different levels of depth of field, between images when you change aperture.
Several processing programs, including Photoshop can work with HDR imagery to blend them together into one uniformally exposed image.
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