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Large scale point clouds rendering with PagedLOD


 
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saedrna1
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PostPosted: Fri Mar 08, 2019 8:01 am    Post subject:
Large scale point clouds rendering with PagedLOD
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Hi,

I am now doing point clouds rendering (probably city-scale) using osg.

The point clouds are indexed using entwine (https://entwine.io/) to the ept format.
Basically, we know the bounding box of the entire scene, and the point clouds are saved to disk with the name D-x-y-z.laz, where D is the level of the octree and x,y,z are the coordinates in the octree.

Each child level, in the octree, is strictly subdivided by 2.

In addition, the levels are drawn additively. For example, 0-0-0-0.laz is the root, when I want to also show it's sub level 1-0-0-0 1-1-0-0 1-1-1-0 1-0-1-0, the four childs and 0-0-0-0 are both draw.

So I have two questions,

(1.a) I want to convert the EPT format, to the pagedlod format and saved as osgb file, is it possible for pagedlod that both parent and it's child are both drawn?
Or (1.b) if it's better that for an additional plugin reader to do the magic? I only read the ept metadata file and return a pagedlod node, and the magic all happens in the plugin?

(2) The laz file also contains other attributes, such as lables (interger), return number (interger), I also want to implement shaders to render color by different attribute, is it possible to save these attribute in osgb and correctly bind the vertext buffer to the same program location?

Thank you!

Cheers,
Han
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Chris Hanson
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PostPosted: Fri Mar 08, 2019 4:08 pm    Post subject:
Large scale point clouds rendering with PagedLOD
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Quote:
(1) I want to convert the EPT format, to the pagedlod format and saved as osgb file, is it possible for pagedlod that both parent and it's child are both drawn?


  Normally, no. OSG's underlying Group system allows only one LOD to be drawn at a time, though lower LODs are actually retained in memory as loaded.


  The way most OSG PagedLOD databases are built (the way VPB for example builds databases) is that LOD 0 will be the low-res version and LOD 1 will contain four sub-pieces at higher res, each of which is the LOD 0 of another PagedLOD.


  You could either


1. Write a specialized variant of PagedLOD that displayed the lower LOD automatically (not recommended)


2. Build your PagedLODs carefully so that PageLOD level 0 contains the lowest detail point data, and LOD 1 contains that same data PLUS the four child PagedLODs. I believe if you link things together properly, the two copies of LOD 0 will only be stored in memory once and drawn once.


Quote:
(2) The laz file also contains other attributes, such as lables (interger), return number (interger), I also want to implement shaders to render color by different attribute, is it possible to save these attribute in osgb and correctly bind the vertext buffer to the same program location?


  Yes. You can store these values as attributes and access them in a shader to control rendering.
 
Quote:
Thank you!
Cheers,
Han
 

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