[osg-users] Advice on how to implement custom file format

[Aaron Andersen]

Hi Robert,

I've dug through the DatabasePager, PagedLOD, and ProxyNode code a bit  
and have a better understanding now. Thank you for the references to  
osgEarth. I'll check out that code and at least have good place to  
start now.

Thank you!
Aaron

Quoting Robert Osfield <robert.osfield at gmail.com>:

> Hi Aaron,
>
> The OSG has a DatabasePager built in, something you can leverage by
> creating a paged database composed of PageLOD nodes, where the PagedLOD
> nodes have file references to the tiles you want to load.
>
> You can either use files directory or encode a tile via the filename string
> and have the plugin that does the loading unpack the details of what to
> load.
>
> The VirtualPlanetBuilder tool creates native OSG paged databases from DEM's
> and imagery, using the PagedLOD to create a paged quad tree hierarchy of
> files and subgraph they map too.
>
> The osgEarth NodeKit also uses PagedLOD but creates the tiles on the fly
> reading the DEM and imagery on demand rather than re-processing like VPB
> does.
>
> Both VPB and osgEarth provide examples of PagedLOD usage, but with the two
> approaches - loading pre-processed tiles directory or using a pseudo loader.
>
> Robert.
>
>
> On 16 August 2015 at 22:11, Aaron Andersen <aaron at fosslib.net> wrote:
>
>> Hello,
>>
>> I'm planning to render a custom (preexisting) map file format using osg
>> and was looking for some guidance. I haven't been using osg for that long
>> so I figure it is worth asking if there is either a way to adapt some
>> existing code in the library to fit this custom format, or if not, what
>> people might suggest as a good way to go about implementing loading and
>> rendering this map file format with osg.
>>
>> The map is composed of individual 3d mesh tiles of variable size that are
>> "snapped" together side by side somewhat similar to toy Lego blocks. Most
>> mesh tiles are relatively small so there are a large number of these mesh
>> tiles required to draw the map. As for the file format itself, the map is
>> broken up spatially into many separate files (known as "regions").
>>
>> I wish to write some code so that the map will be read into my application
>> and populate the scene graph seamlessly so there won't need to be a loading
>> screen every time the camera zooms to a new area of the map. The maps
>> stored in this format are *way* too large to load into memory all at once,
>> so I will need to stream data in as the camera approaches new areas and out
>> as it leaves other areas, always keeping the scene graph up to date.
>>
>> I should mention that the map file format is a little peculiar in that
>> none of the 3d mesh tiles have any absolute position information listed at
>> all. Each and every mesh tile is placed relative to the an adjacent mesh
>> tile. I can arbitrarily choose any mesh tile from a map file and place it
>> at 0,0,0 and from there start placing adjacent tiles, and for each adjacent
>> tile place the adjacent tiles, recursively over and over, to build up the
>> map. I mention this placement peculiarity because it means that I can only
>> ever know the absolute position of any mesh tile that is relatively close
>> to the camera (ie. the area of the map I'm currently rendering).
>>
>> If any clarification is required please let me know and thank you kindly
>> for any advice anyone can offer me.
>>
>> Aaron Andersen
>>
>> _______________________________________________
>> osg-users mailing list
>> osg-users at lists.openscenegraph.org
>> http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
>>