[Bf-cycles] Could we do this with Cycles ?

Dr. Antoine Cottin a.cottin at carbomap.com
Fri Feb 28 15:45:42 CET 2014

Thanks Brecht for the full and develop answer,

> If you want to modify the source code locally to do this, then it may
> be relatively simple. If you want this to be accepted in an official
> Cycles release, it's more complicated because it has to align with our
> goals, I would only add functionality like this if it also benefits
> rendering to create "pretty images" basically. It may be that this
> fits but I don't fully understand what is needed here.
Nothing official here… just some scientific dev.

> There's two things I can see missing in Cycles here: support for this
> light type and the ability to extract the distance. Cycles also only
> does path tracing, nothing bidirectional. Maybe that's not enough for
> you, I'm not sure.
I’m kind of confuse how the distance is not extracted.
it probably computed somewhere (during intersection computation), no, or at least the intersection coordinates ?...

> For the light beam you'd have to implement a new light type. If you
> search the source code for "spot" for example you should find all
> places where a spot lamp is used, and you could copy that code and
> modify it add support for your new light type. Lights need to
> implement an "eval" and "sample" function, one used for evaluation
> after BSDF direction sampling and the other for sampling a point on
> the light. If this is a perfect laser I think you only need to
> implement "sample" because the probability of sampling the BSDF in the
> right direction would be zero.
Thanks will look into that...
> For extracting the distance, is that a kind of render pass or is it
> written out in some other way? If it is a render pass you could
> implement your own render pass type to store this distance, again
> looking at some existing render pass and copying the code. We don't
> currently support custom render passes, if we did perhaps it could
> have been done with shader nodes or an OSL shader.
> But I'm not sure if you expect the output to actually be RGBA +
> distance render passes. If instead you need to send some number of
> rays from the light and then somehow dump them to a file, then you
> need to do bigger changes.
> Brecht.
> On Tue, Feb 25, 2014 at 10:58 PM, Antoine Cottin <adancottin at gmail.com> wrote:
>> Hi,
>> My name is Antoine. I'm a senior developer at Carbomap. Our core business is
>> forest monitoring using airborne laser scanner (lidar).
>> You might have seen some of our graphics/video on BlenderNation lately:
>> http://carbomap.wordpress.com/2014/02/11/free-forest-mapping-graphics/
>> https://www.sharein.com/invest/pitch/508176573/mri-scan-for-forests
>> We are currently designing a new multi-wavelength lidar system (hardware and
>> software) specifically tailored for forest monitoring. For this I have
>> developed a ray tracing engine in IDL (www.exelisvis.com) to simulate the
>> system response. We use Blender to create our 3D virtual scene/world.
>> This setup works but is a bit tedious as we need to export the scene to a
>> specific file format and then process the file into our engine. I also think
>> that we could benefit (and not need to reinvent the wheel) from all the
>> texture/material already present into Cycles... bottom line this would
>> facilite the implementation of the overall simulator.
>> So I was wondering, as a Blender user, if the direct integration of our
>> simulator into Blender could be easily achievable.
>> Basically what we need to simulate the system response is:
>> - a mesh light that project a light beam with a 2D gaussian shape (kind of
>> spot light) -> this act as the laser source
>> - a camera -> this act as the optical scanner/PMT photon detector
>> - and the ability to get the travel distance camera-object-light -> to model
>> the time response system
>> - and the shader value/response -> to model the light/mater interaction
>> (similar to physical render based engines)
>> So two questions:
>> 1. Do you think this could be easily easily?
>> 2. If so, does anyone has valuable guidance on how to get started?
>> PS: I've been already scouting the source code, and I can somehow understand
>> the overall structure/sens of it, however it is always difficult and
>> intimidating to get into a huge piece of code with any guidances/help. Not
>> to mention that C++ is not my native language... so still struggling and
>> stumbling sometimes.
>> PS2: We are a commercial company, but we don't see (nor seek) any commercial
>> outputs from this development, beside being able to design and develop a
>> better hardware. If we succeed, we will most likely release this simulator
>> to the public and scientific community.
>> Thank you for your time.
>> Cheers.
>> Antoine
>> -------------------
>> Dr Antoine Cottin
>> Senior Software Developer/Analyst
>> Carbomap Ltd.
>> 7th Floor, Appleton Tower
>> 11 Crichton Street
>> Edinburgh
>> EH8 9LE
>> http://www.carbomap.com
>> +44 (0)7577 444-046
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