Georeferencing with the new LogDump

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Georeferencing with the new LogDump

Postby Yups » Sat Sep 21, 2013 1:49 pm

Hello!

I am really happy with the new LogDump in qgroundcontrol and the new features in the firmware.

But there ist still one thing missing, to have a perfect platform for taking aerial pictures.

Sync the triggerevent coordinates with the pictures.

Select the folder with the source jpgs, select the log, check jpg and log time to avoid wrong selections. (with a definable time range).
Very important is a customable delay for the camera trigger. Some cameras have an delay of 0,5s.

It would be great to have very precise referenced pictures.

Lat, Long and Alt must be written in the EXIF-Data.
This can be done with the free EXIF-Tool by Phil Harvey: http://www.sno.phy.queensu.ca/~phil/exiftool/


best regards from Germany
Yannick
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Re: Georeferencing with the new LogDump

Postby Max » Sat Sep 21, 2013 8:42 pm

Hi Yannick,

There are plenty of photo tagging apps out there that are very full featured. LogDump gives you a log file to feed into those programs. There IS a camera trigger delay in the latest logDump (also in QGC 1.3 RC1). So you can narrow down the export only to triggered events, and match against a folder of photos on a consecutive basis (photo 1 matches 1st trigger point, photo 2 goes with the 2nd, and so on). Or use LogDump to determine the actual time offset of all your pictures, and use "traditional" tagging based on photo time stamp (still accurate to the second with most cams).

I don't see how logDump would be any better at matching your photos to the log than any other decent tagging software. Am I missing something? The only thing better I can think of is if either the camera could store external data with a photo (feed it lat/lon from AQ) or if a photo ID, from the camera, could be stored in the AQ log somehow. Neither sound very realistic.

Cheers,
-Max
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Re: Georeferencing with the new LogDump

Postby Cookiemonsta » Sun Sep 22, 2013 12:41 am

I can recommend geosetter for doing this ;)
It's free and very good.
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Re: Georeferencing with the new LogDump

Postby Yups » Tue Sep 24, 2013 4:30 pm

Thanks for your relplies!

I already know Geosetter.

The problem i have in mind is very simple. Two things could be a problem:

1st: The camera misses one shot, so the complete alignment is wrong
2st: The camera takes one picture more than expectet, same problem

Both problems are common. One possibility is the alignment by time, as Max already mentioned. But it is not precise.
When the Copter flies with ~ 10m/s, the resolution is 10m...

So we need a combination. The Time must be in a certain range, maybe about 3-5 seconds, but the definite alignment should be made with the TriggerEvent.
;)

Best regards
Yannick
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Re: Georeferencing with the new LogDump

Postby Max » Wed Sep 25, 2013 12:00 am

Well my point is that the AQ doesn't know when your camera actually fired, or if it fired at all. W/out some kind of sensor that can detect what the camera is doing, or a way to feed position data to the camera, I'm not seeing how the data can be improved.

Using the trigger delay options one can get as accurate as possible right now. The timetamp of the photo doesn't have to be precise, just needs to match uniquely with an exported log record (there can't be 2+ photos taken within the same triggering moment). It should work as long as there is sufficient time gap between photos (eg. if you're shooting every second, that could get confusing).

Accurately geotagging photos taken at 10 m/s is going to be challenging. You need a camera that fires with a very predictable delay (fixed focus, etc). Also GPS isn't super accurate to begin with, so some error will be introduced anyway.

Actually I think feeding precise position data into the camera would be ideal, especially since the photos will then come out already tagged. I'm not sure if there are any cameras out there right now capable of that. I know you can get cameras with built-in GPS, but those typically aren't very accurate due to size/antenna/cost constraints (I do have one and it's pretty cool for vacations and such, but it's not a precise instrument).

Cheers,
-Max
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Re: Georeferencing with the new LogDump

Postby Max » Wed Sep 25, 2013 12:21 am

Here are some cams with data input (position) capability: http://www.tetracam.com/Products1.htm Not cheap though, and fairly specific to vegetation surveying.

One way to detect when a camera fires would be to use a hotshoe or other remote flash interface.

-Max
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Re: Georeferencing with the new LogDump

Postby Yups » Sat Oct 05, 2013 10:59 pm

Max wrote:
One way to detect when a camera fires would be to use a hotshoe or other remote flash interface.

-Max


Max! This is probably the best idea! Nearly every (interesting) camera is able to sync external flashlights. It would be VERY accurate, no delay,... ;)

Is there a way to use one PWM Port from the Autoquad as an Input? I think it should be no bigger problem to record lat,long,alt for each shot.

Sorry for my reply, i didn't get any notifications.



Best Regards
Yannick
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Re: Georeferencing with the new LogDump

Postby Yups » Mon Nov 25, 2013 10:25 pm

Has anybody thought about this solution? ;)

Yannick
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Re: Georeferencing with the new LogDump

Postby Kisssys » Tue Nov 26, 2013 3:24 pm

Hello Yannick

Max and I talked about this a couple of month's ago and I did some testing, this was my response.

I soldered a 2.2k 1206 capacitor from pins 2 and 4 ( 1206 size resistor fits between the pins without shorting pin3 ) of the spare pressure sensor and tried my Canon T2 and my Lumix LX3. Both pull the voltage low and is recorded in the log voltage. The T2 holds the line low for 10 ms or so and the lumix was much shorter but recordable. You have to look at the raw voltage to see the change. The camera does not pull the line low with any relationship to what the actual shutter or strobe speed might be.

All of my cameras would take a picture within 150ms if the autofocus is turned off so I'm not too concerned about the delay. That would be a travel distance of 1 1/2 meters at 10ms.

The GPS accuracy and the update rate could easily fall into that.

If the copter was flying at 100 meters and the camera was off vertical by 1 degree, the point that you are looking at is off by 1.75 meters.

If position accuracy of the point is important then the photo is usually corrected to known survey points on the ground.

Those are the reason's I haven't been too concerned about the camera delay.

But reference your question, it should work.


In the FAQ's of http://dronemapper.com/faq read about the importance of ground control points to accurately correct the photo mosaic's that they assemble. It's done for much higher quality images than we can create with a multi-rotor.

Cheers
Steve
Steve
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Re: Georeferencing with the new LogDump

Postby Yups » Sat Jan 04, 2014 1:16 pm

Dear Steve,

thanks for your tests! I use a Sony NEX-5N for my aerial shots because of its weight. The DSLRs are to heavy for long flights ;-)
Yes, with the normal flash connector you will not get any relationship to the shutter or flash speed.
But thats not necessary!

Do you know the Piksi RTK GPS System?
http://www.kickstarter.com/projects/swiftnav/piksi-the-rtk-gps-receiver
50hz update rate and cm-level precision. With this receiver, you would get a new position every 20ms. So it would play a role if you sync it with the camera delay or not. For several cameras, there is only an IR-shutter available -> the delay is not fixed!

The camera angle doesn't matter. You could even fly with a hard mounted cam. Besides Dronemapper thera are agisoft photoscan or Pix4D. All of them use Aerial Triangulation, so its no problem when the cam does not point directly to the ground.

Groundcontrolpoints are one possibility. But you need an extra high precision GPS device wich costs some thousand bucks and the referencing signal costs per minute...

So it would be very useful, to get Aerial Shots with half-meter or 1/4 meter precision (this should be possible with the AQ GPS) WITHOUT additional GCPs.

Best regards from Germany,
Yannick
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