[osg-users] [vpb] vpb generated .osga model seems disturb shared memory in qt4

Robert Osfield robert.osfield at gmail.com
Thu Apr 21 14:49:14 PDT 2011


Hi Rob,

On Thu, Apr 21, 2011 at 10:24 PM, Rob Radtke <rob at stellarscience.com> wrote:
> A co-worker of mine recently fixed a bunch of similar VPB issues by
> following this advice:
>
> http://forum.osgearth.org/Critical-issue-with-paging-and-horizon-td5789174.html
>
> The jist of it is this:
> 'Try setting your OSG_MAX_PAGEDLOD environment variable to something higher
> (default is 300 if I remember correctly).  Also, try changing your loading
> policy to "preemptive" since that way the current LOD is loaded first. '

>From the thread it sounds like tiles may well be overly fine grained,
and that the cost of recreating tiles is very high.  This might be
more common with osgEarth databases, but for VPB generated databases
my experience is that for default settings things balance out without
performance issues.  Use of GL texture compression might well be an
issue as well - VPB databases use GL compression which is lightweight
to download to the GPU.

Upping the maximum number of PagedLOD will give you more headroom if
you system can handle it, how far you can safely go will depend upon
how much data you have in each tile and how much memory you have
available, this is of course something that will vary of dataset to
dataset and from system to system so isn't something the OSG can
pre-empt with perfect defaults for all scenario's.

However, I would add, a low PagedLOD results in lower memory usuage,
but greater bandwidth and CPU load. In all cases though, it will just
me handling OSG and GL specific memory, it shoudln't touch
applications other memory usage other than to contend generally for
the systems resources.  So for Lv I suspect OSG_MAX_PAGEDLOD will be a
red-herring and problem is likely to be elsewhere in the app.

Robert.



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