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Author Topic: Combining terrestrial (ground based) photos with aerial (uav) images  (Read 18558 times)

Shovelhead

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I started using a DJI phantom 4 pro to collect nadir and oblique images that I will be processing in photoscan. As a professional surveyor I will be using the output I get in photoscan to create topographic site plans mostly. The issue I face is modeling the ground under tree canopies, in between fences and sheds/houses ECT.
I would like to use terrestrial images to fill in the gaps so to speak. I am looking for any tips out there on how to go about this. Also any recommendations on what I should look for when purchasing a camera. Would a GPS enabled camera be beneficial?
« Last Edit: April 15, 2017, 04:37:02 AM by Shovelhead »

Packy_GIS

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Re: Combining terrestrial (ground based) photos with aerial (uav) images
« Reply #1 on: April 15, 2017, 08:32:06 AM »
Hi there,
based on my experience - combining aerial and terrestrial images requires the following:
1. high resolution images containing a lot of detail - you shoot much more detailed images from the ground than from Phantom (I don't know what kind of camera you use)
2. There has to be a good overlap inbetween the images - from my experience - oblique images from the "2nd floor elevation" are good.

When I do such a type of modelling - I collect nadir images (as I was producing orthophoto), then I take camera with zoom lens and fly around the site shooting oblique imagery. And if there is not enough detail I take the camera in hand and I shoot additional imagery.

Neverless to say - I don't use UAV but MAV (small aircraft) because in my country it is illegal to fly drones in inhabitted areas and around buildings.

See some examples of our results: Here and Here
Jan

Shovelhead

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Thank you for your informative reply.

Any more users out there with experience doing this? Should I buy a dslr with integrated gps and similar MP (18-24)? Any other tips?

Is there anything else I should look at when choosing a camera?
« Last Edit: May 11, 2017, 05:59:12 PM by Shovelhead »

FlyRight-3D

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What degree of spatial resolution are you trying to achieve?  I have a Samsung NX1100 with a gps module and I can only get accuracy of about 10m from the ground.  The sUAS is around a meter. I have been messing around with this same issue only a little bit but from my experience, the difficulty getting ground based imagery to "sync" with your aerial imagery is overlap. 

Try using some gps coded markers under trees or in those tight spots that will be in the fov of your Aerial imagery so your ground based photos can have a point of reference.  I would also consider trying to elevate yourself as much as possible to capture more of an oblique angle rather than a perpendicular shot. 

Please let me know how this works out for you.

Jeremiah_ROWE

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This is a huge area of interest to me as well. I am in the commercial world now so I can't do as much testing as I had when I was with a research institute. I hope to be purchasing my own personal Phantom 4 Pro next month and would love to do some experimenting in this area.

Packy_GIS - Thanks for sharing your suggestions and work examples. I will use your tips!

Shovelhead - I have found the accuracy on the DSLR GPS units to be relatively poor, keep that in mind when selecting. They are about the same or less than cellphone GPS data output.

FlyRight-3D - Thanks for your input. I am glad that you can verify experience with low accuracy GPS generally found on consumer camera.
« Last Edit: May 12, 2017, 02:54:33 PM by Jeremiah_ROWE »

Shovelhead

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I will definitely be using gcps, I figured the gps would just help with the alignment process. And I was thinking of also using an extension pole to get images about 15' off the ground.

Ive been looking at the Nikon d5300 (http://www.nikonusa.com/en/nikon-products/product/dslr-cameras/d5300.html#tab-ProductDetail-ProductTabs-TechSpecs) because it has GPS and Wi-Fi (remote trigger) and relatively decent specs for the price although it does have an electronic shutter. Thoughts on this model or can anyone suggest something better?

Jeremiah_ROWE

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Using a painters pole or something along those lines would be good. Might want to consider a smaller format to keep the weight down. The m4/3 mirrorless camera systems from Panasonic and Olympus would be worth looking into as well.

Shovelhead

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I was planning on getting a pixie pole - www.polepixie.com

Shovelhead

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Update: purchased a nikon d5300 and took a series of terrestrial shots. Most were able to align and cleaned up the model significantly. This will be a valuable tool to have on many jobs.

Jeremiah_ROWE

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Please let us know how you integrated the D5300 imagery.

Did you align it as separate chunks? Geo-referencing was with built-in camera GPS?

Thanks in advance for sharing your experience!

Shovelhead

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Re: Combining terrestrial (ground based) photos with aerial (uav) images
« Reply #10 on: May 16, 2017, 04:01:15 AM »
I just added the terrestrial photos and did the workflow over again (didn't have to pick my gcps again). I plan to purchase a prime lens asap for better results. I was thinking 35mm, is there anything else I should look for in a prime lens?
Also am I supposed to be processing both sets of images separately due to the different camera calibrations or does photoscan automatically take care of that?

Yoann Courtois

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Re: Combining terrestrial (ground based) photos with aerial (uav) images
« Reply #11 on: May 16, 2017, 10:52:14 AM »
Hi everyone !
I'm actually doing my master thesis in photogrammetric methods for topographic surveys.

Some tips I could give you:
- Integrated GNSS data are not mandatory: Indeed they are never better than a couple of meter accurate. So you will need well-known GCPs to accuratly georeference your model. I usually untick pictures georeferencement when handling survey with our Phantom 4 Pro (Really nice camera by the way).
- Ground pictures will permit you to fill your holes under trees: I'm actually using GoPro camera at the top of a pole. Even everybody are scared about fisheye lens for photogrammetry, I can tell you it's possible ! I was actually able to handle super high accurate measurement using GoPro (I mean sub-millimetric accuracy)
- The secret is overlapping: The more your pictures overlap each other, the strongest will be your model. And don't be scared about number of pictures. I've actually noticed that a stronger bloc with a huge amount of pictures can be calculated faster than a smaller number of pictures weakly linked. (Here is where GoPro camera makes it stronger because of the laaarge field of view)
- Coded targets give you the possibility to save a lot of time in processing: and will give you more confidence on reconstruction. I postpone you to my topic talking about coded target size before print them.

Hope it helps !
Regards
« Last Edit: May 29, 2017, 03:39:03 PM by Yoann Courtois »
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cadm8

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Re: Combining terrestrial (ground based) photos with aerial (uav) images
« Reply #12 on: May 16, 2017, 11:36:36 AM »
handling survey with our Phantom 4 Pro (Really nice camera by the way).

check this first:
http://www.phantompilots.com/threads/p4p-image-not-true-20mp.111480/

Yoann Courtois

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Re: Combining terrestrial (ground based) photos with aerial (uav) images
« Reply #13 on: May 16, 2017, 12:41:34 PM »
Would you say it's not a nice camera ?
Do you have better to offer :) ?
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Yoann COURTOIS
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cadm8

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Re: Combining terrestrial (ground based) photos with aerial (uav) images
« Reply #14 on: May 16, 2017, 03:38:47 PM »
Actually we're using a P3P, so the P4P sensor etc is a big improvement, but you have to consider what the reality is and that it is not true 20MP...