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Author Topic: How high an overlap percentage is too much?  (Read 2334 times)

Brit

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How high an overlap percentage is too much?
« on: January 15, 2019, 02:23:40 AM »
How high an overlap percentage is too much?

I recently used Drone Harmony to scan in a nearby hill with a tree on it's peak (a phenomenon called pedestal erosion). I decided to redo the following day. One calculates the overlap when programming a mission, though guessing the correct distance from the subject, and gimbal angle can be challenging.

 However when I return the google map under the "mission" was missing since I was out of cell phone range, so I used DJO Go's tack orbit, which allows gimbal adjustment and distance on the fly.  I clicked away on the photos as fast as I could as it spun around the hill (RAW images on a Mavic 2).

I may have taken too many photos with too much overlap. It is now the second day of processing these images on Photoscan on my new lap top (with pretty close to the latest and greatest CPU, GPU ...and with 32 gigs of RAM). It says I have another day to go for the dense cloud calculation! I have the setting on "high".

Would it work about as well (but calculate much faster) with a setting on "medium"...or should I remove ever other image in the orbits to speed things up on future orbital scans. Perhaps being too lazy to mask out the sky and clouds (along with the moving cloud shadows) also screwed things up (though we'll see how it turns out...maybe tomorrow)? 

What should the overlap percentage for obits be?
« Last Edit: January 15, 2019, 02:33:48 AM by Brit »

3create

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Re: How high an overlap percentage is too much?
« Reply #1 on: January 15, 2019, 02:34:16 PM »
Hi Brit,

a few things come to mind if you need to reduce processing time for your scene:
  • RAM: I always have the Task Manager running when processing scenes. If more than 32 GB are used in your case, processing will take too long
  • Region: the Region seems rather large. Check if you can scale it down to just the hill
  • Medium vs. High: the performance penalty for High quality is VERY large. Medium should be fine with Mavic 2 images (of course depending on the LOD you require)
  • Orbits: I've found that 5 degrees (=72 images) is on the safe side, but I've also had sucessful turntable scans with 10 degrees

Brit

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Re: How high an overlap percentage is too much?
« Reply #2 on: January 15, 2019, 11:26:18 PM »
Thanks for the suggestions. I just went into the room where the laptop lives and saw that Photoscan had crashed and Windows had re-booted the computer this morning - 2 days into the calculations for the dense cloud.  I am trying again. I made the regions slightly smaller (though I want some neighbouring hills in the final mesh). And I changed the dense cloud setting to “medium”, but I kept the next stage, the mesh settings, to include the depth map quality at "high" and the mesh at 4 million (for now…it saves each step in the batch processing). The Task Manager showed that it never got above 30 RAM the first time around (when I was checking it every few hours).
« Last Edit: January 15, 2019, 11:47:08 PM by Brit »

Brit

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Re: How high an overlap percentage is too much?
« Reply #3 on: January 20, 2019, 07:29:04 AM »
The medium cloud was about far faster (in a couple hours), but the resolution was ... well, medium - not great quality. The high res cloud was much better but it took about 20 hours to calculate. (they were rendered in 3Ds Max using the scan-line and no shadows) I also tried one masking the clouds. It calculated a bit faster but was not much of an improvement. I'm sticking to the high res. Making the area smaller did speed it all up dramatically (the first calculation crashed while going onto the second day of calculating). Thanks for the suggestions!
« Last Edit: January 20, 2019, 07:33:47 AM by Brit »