11x P&S Cameras Rig, little help needed?

goriskil

« on: 07 / January / 2016, 17:12:42 »

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Hello, i have Cannon Powershoots CHDK supportered cameras- 5x A2500 and 6xIxus 132, i have them in a RIG, they all should shoot at the same time to capture the subject (human face) from several angles at the same time (with as little delay (in ms) as possible). In the near future i might buy additional 9 cameras so i would have 20 camera rig, so any solution you propose should work both with 11 cameras and 20 cameras.

Questions:
1) Im planning to use capture via PC (connection via usb cables (cameras go to active USB 2.0 hubs (3x-4x) which are connected to PC via 3x-4x USB cables). Currently im using CHDK_PTP software (im using the graphic (GUI) addition. Will this software in its current version (January 2016) be able to capture (in synchronization) the shoots from 11 cameras (and 20 cameras later on) at the same time?

2) Which are alternatives to GUI CHDK_PTP for Multicam Capture? I found ptpcam but it doesnt run
when i launch it nothing happens, but maybe i have to have cameras connected while trying to run it?)?
What are other alternatives? I know USB remote but i would have to buy the trigger, and i would rather trigger it all via computer, if it is possible?

I know there are a lot of threads about this, i tried to read some and will read the rest, but the situation might have changed since their creation and im asking some new questions, thats why im starting new topic.

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reyalp

13622

Re: 11x P&S Cameras Rig, little help needed?

« Reply #1 on: 07 / January / 2016, 17:37:40 »

Start here: http://chdk.wikia.com/wiki/Multiple_Cameras_using_CHDK

Quote

1) Im planning to use capture via PC (connection via usb cables (cameras go to active USB 2.0 hubs (3x-4x) which are connected to PC via 3x-4x USB cables). Currently im using CHDK_PTP software (im using the graphic (GUI) addition. Will this software in its current version (January 2016) be able to capture (in synchronization) the shoots from 11 cameras (and 20 cameras later on) at the same time?

If you mean a ready to use solution where you just have to click some buttons, no, but it can be done with some work on your part. mphx has successfully built a rig using chdkptp, see: http://chdk.setepontos.com/index.php?topic=11667.0

Unless you want to write a lot of software yourself, chdkptp is probably your own viable option for USB software control, ptpcam is much more limited.

You can also do pure hardware control using USB remote remote for triggering, or combine it with chdkptp for file transfer. The hardware remote will give you substantially better sync.

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goriskil

Re: 11x P&S Cameras Rig, little help needed?

« Reply #2 on: 07 / January / 2016, 18:17:49 »

Thanks for reply, yeah i knew about all those threads you posted, dont worry im not that dumb or lazy and wasting your time

. But i read them only partially they are huge and maybe something changed since they were written... I will focus mainly on that multicam thread with 35 pages tommorow.

Ok so i can scrap the ptpcam solution straight away, good to know that.

Whats currently the sync delay while running the chdkptp with maximum of 20 cameras? How much delay can i expect in ms? Does someone know...? I think that for my purposes with "only" 20 cameras the delay could be manageable... what is it?

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reyalp

13622

Re: 11x P&S Cameras Rig, little help needed?

« Reply #3 on: 07 / January / 2016, 21:56:07 »

Quote from: goriskil on 07 / January / 2016, 18:17:49

Thanks for reply, yeah i knew about all those threads you posted, dont worry im not that dumb or lazy and wasting your time . But i read them only partially they are huge and maybe something changed since they were written... I will focus mainly on that multicam thread with 35 pages tommorow.

I understand, it's a lot of material and things have changed over time... but it's what's available. So far no one has publicly documented one of these projects in more digestible format. I would certainly welcome anyone posting more detailed write-ups!

Sometimes skimming backwards through threads is more productive than starting at the beginning.

Quote

Whats currently the sync delay while running the chdkptp with maximum of 20 cameras? How much delay can i expect in ms? Does someone know...? I think that for my purposes with "only" 20 cameras the delay could be manageable... what is it?

Do you mean the delay between when you command shot and when the shot starts, or spread between the times each cameras shutter opens?

The way the chdkptp multicam script work is:
1) the init_sync function attempts to estimate offsets between each cameras 10ms precision tick counter and "real time"
2) When you shoot, a command is sent to each camera telling it to shoot at a particular time in the future, as a tick count calculated from the offsets in #1

So the delay between sending the command and the cameras shooting scales linearly with the number of cameras, due to the time required to actually send the commands. For reasonably modern cameras like yoursm 5ms per camera should be a decent ballpark, plus a few tens of ms in fixed overhead. (This is ignoring the half-press you need to do beforehand to get all the cameras ready to shoot.)

The spread between each cameras shots depends on the quality of the sync estimates, the precision limitations of the counter, and uncertainties introduced by the cameras task scheduling and shooting code. It shouldn't really depend on the number of cameras, except that with more cameras you will cover more of the overall distribution in any given shot.

I haven't measured this rigorously, I only have a few cameras (all of different models) and I haven't set up a precision test rig. From the limited testing that I have done and what I know about the cameras, I'd expect it to be ~50ms or less most of the time, probably closer to 30. However, this is little more than a WAG and there could easily be camera specific variations.

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andrew.stephens.754365

Re: 11x P&S Cameras Rig, little help needed?

« Reply #4 on: 08 / January / 2016, 07:31:27 »

goriskil,

in case it could be helpful - I needed to do this http://chdk.setepontos.com/index.php?topic=11490.msg124541#msg124541 to provide just enough comfort with use of multicam ptp sync (but there is some stuff there I still don't fully understand).

I hope it's not just confusing.

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goriskil

Re: 11x P&S Cameras Rig, little help needed?

« Reply #5 on: 08 / January / 2016, 08:55:00 »

reyalp:

Thanks, yeah reading the thread backwards is a good suggestion.

I mean the latency between the first and the least camera on the rig shoot.

andrew.stephens.754365: Thanks i will read it

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reyalp

13622

Re: 11x P&S Cameras Rig, little help needed?

« Reply #6 on: 08 / January / 2016, 15:55:55 »

Quote from: goriskil on 08 / January / 2016, 08:55:00

I mean the latency between the first and the least camera on the rig shoot.

OK, to summarize my previous post: How far each camera's shot is from the requested "real" time should be a random-ish distribution independent of the number of cameras, on the order of several tens of milliseconds.

Actual test data is welcome

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goriskil

Re: 11x P&S Cameras Rig, little help needed?

« Reply #7 on: 12 / January / 2016, 17:46:54 »

ok btw if i would need some help, quick help and answers or even to code something that is missing and i had no time to wait, could somone help me for real money? Im post student and poor but i dont have time :-).

How much would some expert of CHDK or better CHDKptp charge for an hour dedicated to me? (either directly helping me via writing in chat/skype) or coding for me? Im not telling i will be able to afford it, im just curious about the charge per hour? Thanks

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waterwingz

12121

Re: 11x P&S Cameras Rig, little help needed?

« Reply #8 on: 12 / January / 2016, 19:46:29 »

In case you don't get a better answer, most of the people with the skills to help you are not here for the money. So unless you really need a response faster than our average of less than 12 hours or so, that should not matter.

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goriskil

Re: 11x P&S Cameras Rig, little help needed?

« Reply #9 on: 12 / January / 2016, 19:55:17 »

Also as far as i understand, when running the multicam.lua "Stuff", to use it to take synchronized shoots with multiple cameras (like 11 in my case) i have to have 2 scripts- one type on the SD card in each camera and then the second type running from my PC through chdkptp, right?

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