Mission planning complex urban mapping with buildings

[obw]

Hi there.

I'm wondering if someone have a few tips and tricks on how to plan a mission to scan a large urban area with lots of buildings?

I know this is a complex task, I have experience with regular mapping missions and how to scan and proccess such areas without any complex or tall structures. I've also done some single buildings with OK results. I've tried a few training missions with complex structures and processed some of them, but the models gets a lot of noise. I recon it's the data collected that needs to be better, the workflow in Agisoft is not a problem I guess.

I've read a couple of other threads here on Agisoft, and some guides from other websites, but I'm struggling to find the best workflow for this type of mission. A regular mapping, even with over 90% overlap simply won't cut it. The building facades won't get any points so I need oblique/tilted photos. The problem is how to capture these photos and how close to the buildings. I've tried to add a large circle with angled photos, but this is not enough to get details, and just adds a lot of noise to the model.

Would it be a good way to fly with a slighty forward tilted camera, and fly the mission 2-4 times in diffrent directions? Do I need to circle every single building to get the best results? Or maybe start off with a large circle tilted towards center, and add several other circles towards the center?  I'll attach a screenshot from Google Earth (Even they make good 3D models from urban areas)

[SAV]

Hi obw,

I suggest to fly 2 'standard' surveys perpendicular to each other with the camera NOT pointing straight down (=nadir), but oriented at 10-35 deg from nadir. You should try to avoid the horizon/sky in your aerial imagery.

Here are some more details:
https://support.pix4d.com/hc/en-us/articles/202557459-Step-1-Before-Starting-a-Project-1-Designing-the-Image-Acquisition-Plan-a-Selecting-the-Image-Acquisition-Plan-Type#label8

All the best.

Regards,
SAV

[obw]

Interesting, thanks for your tip SAV. I totally missed this from their website.

Are there any considerations regarding processing of such areas, compared to a regular mapping?

[SAV]

Hi obw,

No problem. The Pix4D support pages are generally quite good.

Regarding processing settings. For the mesh use '3D arbitrary' instead of 'height field' and when building your texture choose 'adaptive orthophoto' in order to achieve properly textured facades. 

Also use a high image overlap (80-90%) when acquiring the aerial images, and make sure that all images are sharp, properly exposed and have low noise levels (ISO). Also manually set the white balance to match the weather conditions (sunny or cloudy).

In case you are using a DJI P4 Pro or DJI P4 Advanced, remember to enable the MECHANICAL SHUTTER in the DJI GO 4 app.

And last but not least, stick to the local UAV regulations

Regards,
SAV

[obw]

Thanks, most of that are already in my normal workflows, so it should be OK You helped me with the rolling shutter issue in another thread, so that's been thoroughly researched the past couple of weeks, I see that more and more people are becoming aware of the issue.

I work in a UAV company were we have all required licences and follow local regulations. Sadly, I see a lot of operators who doesn't follow  local regulations.

[SAV]

Hi obw,

Good to hear that you found previous posts/threads helpful.

I think it is important that people follow best-practice workflows.
This forum is a great way to share experiences and learn from each other in order to get best possible and accurate photogrammetric reconstruction results.

Yep, there are a few 'wild cowboys' out there who don't think that they have to follow local regulations. But it's their own risk. I am not to too concerned about it (even though they might shed a bad light on the 'UAV photogrammetry industry'). In the long term they probably won't survive #problemsolveditself

Regards,
SAV