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Author Topic: workflow for urban areas  (Read 213 times)

andreg

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workflow for urban areas
« on: May 17, 2019, 12:24:28 AM »
Does anyone have an workflow without distortion using DEM or DTM?

- Over / sidelap capture (in the log do I use height relative to the ground or change the height of the pixhawk?)
- Accuracy for alignment, densecloud
- optimization and cleaning

I'm exaltively testing but I never get to a perfect project or close to it.

I'm using a Samsung nx mini to capture the images

Alvaro L

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Re: workflow for urban areas
« Reply #1 on: May 17, 2019, 10:05:20 PM »
Urban areas are the most difficult case for a photogrammetry work. Usually a combination of oblique, zenital and detail pics should work but a good mission planning workflow is very important so you can optimise flights, pics and processing for a good result. I can't go into details but in short your usual planning software and clueless rectangular grid patterns won't work. Your flight pattern and camera angles should adap to urban grid, street width and building heights. I am also against doing it in a on single field data, you need to iterate in your planning approach, model photographing and software reconstruction loop. You need command of several software packages to do it right.

https://sketchfab.com/3d-models/montblanc-4998e976b9894acdaa93ade53075664f

Some universities have published papers about city sampling and reconstruction works, but they use some serious overload of tools and resources we don't have, like combination of laser scanning on car with airplane based areal photogrammetry with rigs that get to shoot several cameras at once plus GCP with total stations, university support and staffing, etc. Even so, I think it can be done exclusively on photogrammetry work if you get to understand what it is going on, for instance how to get pics from ground level and from drone level correctly aligned.
« Last Edit: May 17, 2019, 11:35:27 PM by Alvaro L »

andreg

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Re: workflow for urban areas
« Reply #2 on: May 19, 2019, 03:24:38 AM »
Great answer, I'll look at it deeper. And for my case I only need  a orthosmosaic, do you have any tips or standard workflow for this?
« Last Edit: May 19, 2019, 03:33:56 AM by andreg »

Alvaro L

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Re: workflow for urban areas
« Reply #3 on: May 19, 2019, 06:10:39 PM »
In this case I would adapt fligh lines to urban grid so building do not shadow your street sampling. Take a good GIS cartobase and make your drone follow street center lines and then fill in with intermediate flight lines when overlapping is insuficient in between streets.

Alvaro L

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Re: workflow for urban areas
« Reply #4 on: May 20, 2019, 10:40:42 AM »
However, building rooftops are the ones driving your GSD, so you will be doing a bit of oversampling on street level. If there is a buidling breaking the sorrounding heights you will need a special flight lines just for it.
« Last Edit: May 20, 2019, 10:46:55 AM by Alvaro L »