[osg-users] osgdem --terrain vs polygon count?

Robert Osfield robert.osfield at gmail.com
Mon Sep 29 09:38:35 PDT 2008


Hi J-S,

You need to decide what you want to do, but personally I'd recommend
using --terrain and then in your app decide how much detail you want,
you can make this user definable, provide reasonable defaults for
different classes of hardware 0 they key is it's under your control
and even after the app is deployed you can still tweak things to
better fit the hardware.

--terrain also provide much greater opportunities for compressing the
tiles on disk.  More work will go into this in the future, so tiles
with --terrain will end up being more compact despite have more
geometry detail available when you need it.

Robert.

On Mon, Sep 29, 2008 at 4:20 PM, Jean-Sébastien Guay
<jean-sebastien.guay at cm-labs.com> wrote:
> Hi Robert,
>
>> The main speed up with using --terrain in the osgdem/vpbmaster build
>> is that the tile geometry doesn't need to simplified - it can just be
>> aquired from the source DEM's as grids and then output as grids.
>
> [...]
>
>> The key thing to remember with --terrain databases is that since the
>> triangulation is done dynamically on load you do load balancing - you
>> can set the Terrain::setSampleRatio() according to the hardware that
>> you have
>
> Ok, so in order to get --terrain databases to work optimally on all machines
> I would have to expose this setting in my software's config files (for
> example) so that it can be tweaked according to each machine's hardware, is
> that right?
>
> I would suspect that on relatively flat terrain, the terrain database using
> simplified geometry might run fast enough on all machines (or all reasonably
> fast machines) without losing any relevant detail, whereas the --terrain
> database would be too slow on older machines, which would require that we
> lower the sampleRatio, and thus lose some detail? Is that possible?
>
> In that case, if we need to support a large number of different hardware
> configurations, we might be willing to accept the longer build times of not
> using --terrain in exchange for not needing to tweak sampleRatio and not
> losing any detail.
>
> Thanks,
>
> J-S
> --
> ______________________________________________________
> Jean-Sebastien Guay    jean-sebastien.guay at cm-labs.com
>                               http://www.cm-labs.com/
>                        http://whitestar02.webhop.org/
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