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Mixed resolution databases


 
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bellit
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Joined: 28 Jan 2010
Posts: 5

PostPosted: Fri Aug 25, 2017 1:50 pm    Post subject:
Mixed resolution databases
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Hi,

I am trying to generate a database with very different sets of data resolution:

1. low resolution data (BlueMarble) covering the whole earth.
2. very high resolution data (20cm per pixel) for an area of interest (~30x 30 km rocket launch site)

The plan is to start a flight at the high res area, and end up in orbit of the planet earth.

I tried several ways to achieve this result:

1. All data is used in the same database: Very high levels are necessary, the database gets incredibly big, the generation time skyrockets.

2. using the --levels switch for blue marble data (levels 0-8 ) and high res data (levels 8-18 ): Works in principle, leads to a nasty transistion period, where a complete part of the earth is white (I think where the textures of the low res files are not shown because of the levels statement)

3. using the --patch switch to integrate the high resolution into the low res database: it seems, that the number of levels of a databased can not be increased after the first generation.

So it seems, my only option is to generate insanely huge databases (in an example with 80cm resolutions it got 300 GB large, although only a small part of the earth was covered by high res data).

Maybe there is another way I missed? Is there a way to integrate high resolution databases in low resolution planetary databases without creating very large files?

Kind regards,
Tobias
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robertosfield
OSG Project Lead


Joined: 18 Mar 2009
Posts: 11154

PostPosted: Fri Aug 25, 2017 3:05 pm    Post subject:
Mixed resolution databases
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Hi Tobias,


Paged databases tend to be quite a bit larger than the source imagery as GL texture compression is not as efficient memory wise compared to tiff/jpeg, instead it's designed for high GPU performance so it's usually an appropriate trade off for real-time visualization. 


VirtualPlanetBuilder is written specifically for very large datasets, a paged database of 300GB is actually quite modest, multi-terabyte databases are common when dealling which lots of high res data across the globe.  VPB has support for generating databases using a cluster of machines to help with work in generating the databases.  Reading, processing and writing to disk large amounts of data is rather intensive though, so build times can be quite large.


The focus of VPB is not build speed but generating high performance, large scale paged databases, so you build a few times, but run your visualization application many times.


If real-time performance isn't so critical but you would like to avoid the paged database build time then osgEarth might be the tool to use.


Personally, if you have the disk space and the runtime performance is working well then I'd just build a paged database with all the data you have to high level required (VPB automatically stops build once full res has been achieved) and just have fun,


If you don't have the disk space then there are things you can look at, but at this stage I don't see any reason not to just go with a full res database.



Robert.

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bellit
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Joined: 28 Jan 2010
Posts: 5

PostPosted: Mon Aug 28, 2017 5:35 am    Post subject:
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Hi Robert,

thx for the quick answer, I will fire up the RAID! (time for some more Terabytes...)

Cheers,
Tobias
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