[osg-users] LOD capabilities

[Robert Osfield]

Hi Bruno,

On 26 April 2016 at 16:04, Bruno Oliveira <bruno.manata.oliveira at gmail.com>
wrote:

> the tool I'm creating is designed to handle clouds from 100 million points
> to 1 billion, hence the out of core rendering.
> By "with the already existing code", I mean code from OSG.
>

100 million to 1 billion does qualify as "huge" point cloud.

The issues aren't directly related to the OSG, but how to manage that
amount of data on disk, in main memory and on the GPU.  The OSG itself can
be used to start the data in main memory, on the GPU, and even provide
mechanisms for paging data in out from disk (via PagedLOD/DatabasePager).
You will be responsible for how you set up the scene graph, how you do this
is the crux of the task, it's not trivial given the amount of data you are
dealing with.

When learning what can be done you need to start doing the maths on how
much memory each point in your cloud requires. A single vec3 for each point
for 100 million points requires 1.2 GB, 1 bilion requires 12GB.  When
passing data to OpenGL you need to put the data into OpenGL FIFO which then
gets passed in driver memory.  If you are using VBO's then you'll end
potentially with one copy of data in application memory, one in driver
memory, and then when it finally gets rendered a copy on the GPU too.  This
means we'll need at least 2.4GB main memory and 1.2GB on the GPU just for
100 million vertices - this without anything else.

This is without any colours, normals or textures.  You haven't mentioned
anything about these, perhaps you should... as it makes a big difference to
the memory footprint we are talking about.  I'm not expecting that you'll
just have white points...

So when you start asking can the OSG do it, you can get it to scale to
handling multi-terrabyte databases thanks to the built in paging support,
but only if you give it an appropriately built scene graph - point clouds
are a niche that doesn't have open source tools that will build the
database for you.  You need to be realistic about the memory management,
handling really large amounts of data requires far more skills than just
rendering a few pretty textured polygons.  I don't know what your
background knowledge, what can we assume?

If you don't have the skills right now then you'll need patiently develop
them OR just pay a 3rd party engineer who has the skills to work with you
on it.

Robert.
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