Hi.

Here is my question:

Since around 3 days, POV-Ray (Windows version) rendered a file with photons. 
I used the option "save_file "HeliChopper 02 Gray Fleet on Ground.ptn". 
Since those 3 days, POV creates the photon map. Now I had a power cut, and 
would like to know, if there is an option to continue the photon map file 
building, where it stopped, similar to the "+c" option for the raytracing 
itself.

If for some reason there is not yet such an option, I would herewith suggest 
this feature with a big urgence.

Thanks.

Sven Littkowski

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Sven Littkowski escribió:
> Since around 3 days, POV-Ray (Windows version) rendered a file with photons. 
> I used the option "save_file "HeliChopper 02 Gray Fleet on Ground.ptn". 
> Since those 3 days, POV creates the photon map. Now I had a power cut, and 
> would like to know, if there is an option to continue the photon map file 
> building, where it stopped, similar to the "+c" option for the raytracing 
> itself.
> 

The file is saved only when the whole photon shooting finishes. If you 
have a file on disk, then it's complete (unless the power cut was while 
the file was being written, unlikely).

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Your answer hits my worst fears: after three days working on a photon file 
which has not yet been saved, all is lost!

My question is: why allows POV a scene to be continued, but not a photon 
file?

Please, developers, create the possibility to also continue the photon map 
file after a stop (of which reason ever). POV-Ray partially writes data into 
an image, so it can continue where the previous render was stopped. Could 
the same procedure of partial writing into a file not be applied to the 
photon file, as well?

THIS IS A FEATURE REQUEST.

Sven



"Nicolas Alvarez" <nic### [at] gmailisthebestcom> schrieb im 
Newsbeitrag news:479bc587@news.povray.org...

>> Since around 3 days, POV-Ray (Windows version) rendered a file with 
>> photons. I used the option "save_file "HeliChopper 02 Gray Fleet on 
>> Ground.ptn". Since those 3 days, POV creates the photon map. Now I had a 
>> power cut, and would like to know, if there is an option to continue the 
>> photon map file building, where it stopped, similar to the "+c" option 
>> for the raytracing itself.
>>
>
> The file is saved only when the whole photon shooting finishes. If you 
> have a file on disk, then it's complete (unless the power cut was while 
> the file was being written, unlikely).

Post a reply to this message

Sven Littkowski escribió:
> Your answer hits my worst fears: after three days working on a photon file 
> which has not yet been saved, all is lost!
> 
> My question is: why allows POV a scene to be continued, but not a photon 
> file?
> 
> Please, developers, create the possibility to also continue the photon map 
> file after a stop (of which reason ever). POV-Ray partially writes data into 
> an image, so it can continue where the previous render was stopped. Could 
> the same procedure of partial writing into a file not be applied to the 
> photon file, as well?

Note that when saving a PNG image, the file is only flushed to disk 
every 16 lines. Probably it's also updated when you pause the render; 
but that won't happen on a power failure, so you could lose your last 15 
lines :)

In the case of photons, it looks like they are "sorted" (whatever that 
means) when the photons finish shooting. And *then* they get saved. I 
see no reason why it couldn't save the photons as they get calculated, 
then sort them and overwrite the whole file with the sorted version, so 
that if the render gets suspended before it's done, it could in theory 
load from the file, shoot what's left, and sort the whole thing. But I 
know little about the internals of how photons work, so there may be a 
good reason why it's not done this way.

PS: what are your computer specs? If mine turns out to be better than 
yours, I could give you some CPU time for that insane render.

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YES!!! That would be fine! In addition, you would be free to use the items 
inside there for your own scenes, I do not mind.

Specs:
- Intel Pentium DualCore 3.06 GH CPU
- 2,048 MB RAM (2 GB RAM)
- Scene File Output Resolution: 3,200 x 2,400 pixels

Do you know about "Render Farm" software?

Sven






"Nicolas Alvarez" <nic### [at] gmailisthebestcom> schrieb im 
Newsbeitrag news:479bd45a$1@news.povray.org...

>> Your answer hits my worst fears: after three days working on a photon 
>> file which has not yet been saved, all is lost!
>>
>> My question is: why allows POV a scene to be continued, but not a photon 
>> file?
>>
>> Please, developers, create the possibility to also continue the photon 
>> map file after a stop (of which reason ever). POV-Ray partially writes 
>> data into an image, so it can continue where the previous render was 
>> stopped. Could the same procedure of partial writing into a file not be 
>> applied to the photon file, as well?
>
> Note that when saving a PNG image, the file is only flushed to disk every 
> 16 lines. Probably it's also updated when you pause the render; but that 
> won't happen on a power failure, so you could lose your last 15 lines :)
>
> In the case of photons, it looks like they are "sorted" (whatever that 
> means) when the photons finish shooting. And *then* they get saved. I see 
> no reason why it couldn't save the photons as they get calculated, then 
> sort them and overwrite the whole file with the sorted version, so that if 
> the render gets suspended before it's done, it could in theory load from 
> the file, shoot what's left, and sort the whole thing. But I know little 
> about the internals of how photons work, so there may be a good reason why 
> it's not done this way.
>
> PS: what are your computer specs? If mine turns out to be better than 
> yours, I could give you some CPU time for that insane render.

Post a reply to this message

Sven Littkowski escribió:
 > YES!!! That would be fine! In addition, you would be free to use the 
items inside there for your own scenes, I do not mind.
 >
 > Specs:
 > - Intel Pentium DualCore 3.06 GH CPU
 > - 2,048 MB RAM (2 GB RAM)
 > - Scene File Output Resolution: 3,200 x 2,400 pixels

My computer is an AMD Dual Core 4200+ 2.20GHz, 2GB of RAM. So I guess 
it's slower... And I think I have higher chance of a power outage than you.

 > Do you know about "Render Farm" software?

*I have a renderfarm* currently hosted on IMP (Internet Movie Project) 
server. There's somebody attached with some 8-core machines! Although he 
has some powerful Macs, and I never got round to compiling POV-Ray (with 
my patches) for Mac, so there's some unused power.

http://impfarm.imp.org/boinc/hosts_user.php?userid=36

One problem is that photon mapping *can't* be distributed, in the sense 
that we can't lower the time it takes by throwing more computers into 
it. At least not without modifying POV source in areas I wouldn't dare 
touch. Although, even if it was possible, it would need a lot of network 
bandwidth for all computers to exchange the parts of the photon map they 
computed, before doing the render...

So, each computer would need to compute the photon map completely. And 
since it can't be resumed, that may be a problem for some users who 
wouldn't keep their computers running for 6 days...

<PovAddict> somebody on povray newsgroups has a scene that takes 6 days 
to do a pre-computation that cannot be resumed, I'm wondering if it 
would be acceptable for imp@home to have WUs that spend 6 days computing 
without being able to checkpoint at all
<KathrynM> are you crazy?
<PovAddict> :D
<Rookie_69> That's why he comes here.

Hmm yeah it may be a problem.

And then there is the RAM usage. POV-Ray keeps the whole photon map 
loaded in RAM. There are sub-2GB machines that won't be able to 
participate. Plus, are you sure exactly how much memory the scene will 
use? I think that's impossible to know without computing the whole 
photon map and checking the statistics at the end of the render.

PS: I tried to email you, removing the obvious anti-spam measures, but 
it immediately bounced back, saying "invalid address".

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Nicolas Alvarez wrote:
> <PovAddict> somebody on povray newsgroups has a scene that takes 6 days 
> to do a pre-computation that cannot be resumed, I'm wondering if it 
> would be acceptable for imp@home to have WUs that spend 6 days computing 
> without being able to checkpoint at all

So rent one of Amazon's machines for a week. Probably $20 or so. :-)

-- 
   Darren New / San Diego, CA, USA (PST)
     On what day did God create the body thetans?

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Hi Darren,

can you give me some details about those Amazon machines? How and where to 
gain more information on that? How to contact that company?

Thanks,

Sven



"Darren New" <dne### [at] sanrrcom> schrieb im Newsbeitrag 
news:479c097f$1@news.povray.org...
> Nicolas Alvarez wrote:
>> <PovAddict> somebody on povray newsgroups has a scene that takes 6 days 
>> to do a pre-computation that cannot be resumed, I'm wondering if it would 
>> be acceptable for imp@home to have WUs that spend 6 days computing 
>> without being able to checkpoint at all
>
> So rent one of Amazon's machines for a week. Probably $20 or so. :-)
>
> -- 
>   Darren New / San Diego, CA, USA (PST)
>     On what day did God create the body thetans?

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Sven Littkowski wrote:
> can you give me some details about those Amazon machines? How and where to 
> gain more information on that? How to contact that company?

Go to www.amazonaws.com. (That's Amazon's Web Services, see...)

On the left edge, they list all the web services they supply. Two are 
most notable for people not doing electronic commerce stuff:

The Amazon Simple Storage Service (also known as S3) lets you store 
arbitrary amounts of data out on Amazon's servers for small amounts of 
money (relatively speaking). There are a number of client libraries and 
programs that make it easy to get to it, and so on. (Jungle Disk is 
decent, if you want something that works better than a demo and you want 
to treat the storage like a disk.)

The Amazon Elastic Compute Cloud (also known as ECC) allows you to start 
up a machine running Linux, load it with an operating system stored on 
Amazon S3 (either by you, by Amazon, or by someone else making their 
OS-configuration available to you), and run it. They ten cents per hour 
per CPU (about a 1.x GHz CPU IIRC). You can also rent multi-CPU 
configurations for a multiple of that. (Actually, it used to be twenty 
cents per hour - I wonder what happened.)

It's really pretty easy to set up compared to anything else I've seen. 
You need to have access to SSH (such as putty under Windows). Getting 
the Java command-line stuff working with the right environment variables 
was the hardest part. Once you manage to fire up an "instance" and get 
yourself logged in, it's just a normal remote computer running Linux. 
Follow carefully the instructions in the "getting started" tutorial and 
you'll be online in half an hour.

If you want to do something manually, you can just fire up a machine, 
remote login, scp povray onto it, start it up, and when it finishes, 
copy the results off and shut down the machine.

I've also written a programm I call "oddjob" that lets you set up a 
collection of jobs to be done (e.g., povray image traces for an 
animation), and the program will coordinate N different machines all 
peeking into the list of jobs, pulling down the data files, running the 
program, and storing the data files back into S3, and then shutting down 
the machines as the number of jobs runs out.  I haven't released it yet, 
but only because I haven't had time to set up any sample ECC "images." 
I.e., the program works, but actually firing up the Amazon computers is 
still manual. I'm happy to share the code with you, but it's not really 
targeting what you're talking about here, which is something that's hard 
to distribute amongst multiple machines.

Paying for it is as easy as paying for something you order from Amazon. 
You even use the same account you already have with them, and just pick 
how you want them to bill your credit card at the end of the month. If 
your credit card is funky, be aware they *will* actually charge you 
three cents if that's how much of their services you use. Kind of 
strange, but I guess they do enough traffic to get special contracts 
with their Visa and Mastercard providers and all[*].


[*] Or they bought their own bank, which was one of the suggestions made 
by an investor early in my career. When everyone at the table twitched, 
he added "you can get some small banks quite reasonably these days."

-- 
   Darren New / San Diego, CA, USA (PST)
     On what day did God create the body thetans?

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