UAV for photogrammetry / surveys

Hi Everyone

Im putting together a UAV for aerial surveying using stereo photogrammetry.

Id like to get some input for the experts before going ahead.

My plan is to buy a high wing trainer coupled with an APM2.

Electric powered with a gyro camera mount.

The software Im using is photomodeler scanner. It can do DSM.

Im quite a n00b when it comes to fixed wing, but I have got a fair amount of expericence on multi-rotors.

Im doing this on a fairly tight budget and need to know a good camera to use.

Any advice would be greatly appreciated and will gladly buy any1 a beer if you're ever in South Africa :)

Thanks!

G:)

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Permalink Reply by Gisela & Joe Noci on October 9, 2012 at 2:30pm

@ GeoBlu,

Hi There. Yes, the whole topographical survey world is going to take a new direction once UAV photogrammetry use becomes the norm!

We have just completed a mammoth calibration test program to be able to prove our processes and accuracy of results. In general DEM surveys accuracies do not have to be down to 3 or 4 cm ( horizontal), such as for broader town planning etc. But the mines here want much better than that for stockpile volume measurements. So we executed a program where we photographed a 2.5km X 1.2km area, with a 21mm and a 30mm ( approx equivalent 35mm film camera focal length or 30mm and 45mm respectively). We photographed at 2cm GSD, 4cm GSD and 7CM GSD. We placed 140 ground tie points, 40 of them on the periphery. When we processed the images we used 30 of the periphery points and 50 of the 100 points 'randomly' spread over the full internal area. The area we used had elevation of approx 670m ASL at the North Western corner, 635m at the North Eastern corner, 521m at the South Eastern corner, and 610m at the South Western corner.So, a sort of rectangle with the SE corner draping down quite a bit ( 150meters or so) .

After processing the images and creating the DTM's/contours, etc, we then referenced the results in two ways - first we used all the balance of the placed tie points to measure and test the DTM against.

Then we identified on the DTM some potentially difficult site locations with good visual markers ( 126 new points!!) , ( embankments down to a river area, hillocks, granite ridges, etc) , took XYZ data of these from the DTM, went back to the site and located the visual markers and surveyed the points and referenced them against the DTM data.

The results are complex - not easily explained in a paragraph here! , but in essence -

Where the contours do not rise or fall more than 1meter in every 2meter horizontal distance, our average accuracy is 2.7cm horizontal, and 3.9 to 4.7cm vertical.

In instances where the rise and fall is more abrupt, for example, the sides of a river bed, say dropping 2meters within a 1meter horizontal distance, our average accuracy with 2cm GSD is 3.8cm horizontal, and 4.8 to 5.5cm vertically. ( the worst we saw is 5.7cm horizontal, 7.3cm vertical

At 2cm GSD the horizontal ground point 'creep' over 500meters is less than 5cm. This is the DTM horizontal distance versus actual measured distance over 500meters with NO tie points located between the two measurement points, and with tie points adjacent to this line, not located closer than 100meters to the line between the points - difficult to explain in words...This creep has a direct relationship between number of tie points and lens distortions. Increasing the number of tie points eliminates the effect..

Hope I never need to do this again - took a month of Sundays!

Regards

Joe

Permalink Reply by UAVOZ on October 22, 2012 at 1:46am

@Joe, Could you please tell me how you set and control the Camera (SAMSUNG NX200/210)?. What difference between the Samsung lens and Pentax. I think it has 16mm in the kit. 

Cheers,

UAVOZ


DeveloperPermalink Reply by Antonius Lourenço Kasbergen on October 23, 2012 at 2:13pm

I want to know this too.

Thanks 

Permalink Reply by Francisco on October 23, 2012 at 3:43pm

I think there are three important things that must be together to choose the best camera:
weight, sensor size (22 x 14 mm or higher) and barrel distortion.

To see distortion check

http://www.imaging-resource.com/camera-reviews

To more accurate we need the tangential distortion but it isn´t on the database and I think is too hig

Permalink Reply by Gisela & Joe Noci on October 30, 2012 at 1:42pm
@ UAVOZ..
Regarding how we control the Samsung NX200 -
I open the cameras and connect wires to the focus and snap switch lines. The camera is then neatly closed with a mini connector located in the battery compartment. This is then controlled by the autopilot during the photo mission. The flight plan is set for the correct height and photo interval for the correct photo overlap for the required GSD.

The samsung lenses are no good for this application - they are fly-by-wire lenses and will not remain at a manual focus setting when the camera is switched off and of again. In auto-focus mode they are too slow and the time between photos suffers - we go down to 0.7sec between photos and the lens insists on refocusing each time. The Pentax 21mm lense is superb - very low distortion. Used with the Samsung/pentax adapter which has a manual aperture ring, so easy to set aperture and take photos in aperture priority mode.
The downside is the weight - camera plus adapter plus pentax lens is around 500grams...
Pentax lens is around 240grams, the 15mm pentax lense , also a VERY good lens with low distortion, is even heavier.

The best lense for this is in fact the Voightlander 20mm or 15 mm lense with adapter. it is half the weight of the pentax lens, perhaps better quality in photo, and the adapter is 12grams compared to the samsung 66grams...I have not managed to find the Voightlander lense in my part of the world yet - B&H camera in NYC have them at good prices.

Joe

DeveloperPermalink Reply by Antonius Lourenço Kasbergen on October 30, 2012 at 7:37pm

About the NX200, did you get this info (what to change so you can trigger it via APM) on the net? Or did you tried and learned how to modify NX200? I'm using here in my country a SX260 + GPS, the nature of my work is much simpler than yours and high precision is not a priority, but high resolution is. I'm using SX260 because its GPS and it really helps, and I'm using Agisoft too, and I really likes it. 

But if you can share I really want to know how you did it, or at least point me some site... 

Thanks! 

Permalink Reply by Gisela & Joe Noci on October 31, 2012 at 2:01pm
@Antonius,
No, no info o do this on the net..I opened the camera and traced the wiring I needed in order to connect to the focus and snap connections - need both, even though in fixed focus manual, since we periodically ( every 15 seconds ) just do a dummy focus if not taking photos so the camera does not go to sleep while preparing the flight plan upload, preparing for autolaunch, etc.

It is a real pain modifying the cameras like this, but no other way - cannot use a servo to do it - we take 800 photos on a 1.5hectare area, and have flown over 4500 hectare already - the servos will not last the end to end cycling every 0.8seconds...I have now modified over 30 cameras - 15 Samsung NX200, 9 Canon, and the rest a mix of cameras we were testing.

We never use GPS cameras - we use the aircraft attitudes and position ( from the IMU)and compute the image center on the ground from that and feed that to Agisoft with the photos.

Joe
The NamPilot
Permalink Reply by brakar on October 31, 2012 at 4:25pm
Hi,

With regard to the processing part; anyone who have experience with Apero/MicMac, (open source), who can compare it to the commercial variants of such software?

bromle
Permalink Reply by Daniel Portillo on November 7, 2012 at 5:02am

What used to get GPS accuracies as good with Agisoft perhaps RTK or differential?

Permalink Reply by Duffy on November 9, 2012 at 2:44am

How about, integrating the universal IR remote shutter camera control libray in the MavLink library so different type of cameras can be triggered with an IR LED from one of the I/O pins of the 2.5 board (apologies for double posting this).

 Any ideas of where to start?

Permalink Reply by José on November 12, 2012 at 4:05pm

Dear friends.

Let me recommend you to try to Olympus OMD or the lighter and more recent EPL5 and EPM2

the NX looks finer in terms of pixel count but it does not resolve more detail, so that just makes raw shooting   imposible and further processing and storage over-weighted.

Do not assume that voightlander's and legacy jewel-glass by Zeiss and Leica must deliver better images than plasticy lenses you can find in low-budget shelves. Those lens are designed for film and often they do not perform near as good with digital sensors (this has to do with the angle of light when hits the sensor near the corners) This becomes specially true as focal-length shortens.

the 4/3 format is usually despised for being smaller than APS-C, but this makes it easier to achieve optical designs about to be telecentric.
You have a wider range of prime lenses that are designed specifically for digital sensors in this format.

Oly ZD12mm (superb!!!)
14mm Panaleica (good!)
Oly "cap-lens" 15mm (argueably the lightest and cheapest lens ever made ​​in the world, F8 but useful)
Oly 17 f2.8 pancake (light and cheap, just decent)

New Oly 17 f1.2 mm (promising but not tested yet)

Sigma 19mm 2.8

Panaleica 20 (very good)

Panaleica 25 (wonderful but starts to be too long -50mm equiv)

Lens reset during camera switch can be overridden by setting, but it is not that much an issue as you can self calibrate in most cases.

Permalink Reply by B Duffy on November 15, 2012 at 1:34pm

Have you ever used a Canon camera? I use a point and shoot with CHDK sending a signal from rx to camera via USB (no servo needed) with pretty good results control-wise. The camera itself is low quality but it's all I have right now for testing. I can control it either by autopilot or rc tx and run an intervalometer script at a preset interval. I am wondering if you have any particular reasons for not using a canon such as distortion or otherwise.

Thanks!

Brenden

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