Re: [osg-users] calculating area of the 3d model.

[Uma Devi Selvaraj]

Hi,

  Thanks paul. I will look into it. :)

... 

Thank you!

Cheers,
Uma

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Re: [osg-users] calculating area of the 3d model.

[Paul McIntosh]

Hi Uma,

You might want to also look at VTK/ParaView which has some features but event 
then it is a non-trivial task.

A while ago I needed to calculate the frontal area and it turned out easier to 
just render it and pixel count. The issues were due to how select works. As the 
GPU is optimising the rendering, it is not drawing all the triangles, if you 
then select and calculate on that select you will not get the correct answer.

You may be able to do a variation with slicing and pixel counting (in either 
VTK or OSG) - my random nodes/coda here:

https://github.com/internetscooter/Vespa-Labs/tree/master/VespaCFD/CalculateFrontalArea

Cheers,
Paul

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Re: [osg-users] calculating area of the 3d model.

[Uma Devi Selvaraj]

Hi,

  Thanks for the reply robert and sebastain :)
... 

Thank you!

Cheers,
Uma

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Re: [osg-users] calculating area of the 3d model.

[Robert Osfield]

On 16 November 2016 at 13:21, Uma Devi Selvaraj  wrote:
>  I need to calculate area , perimeter & volume of a selected part or area 
> in 3d model. For example after rendering 3d model, if I select some 
> area(cloased area) , say point1 point2 point3. Point1 connected to point2 
> point2 to point3, point3 connected to point1. Is it possible to do it with 
> the help of OSG.?

The OSG has basic vector maths code that can help with the low level
calculations but there no utility that provides the functionality you
are after - it's very niche application specific task you are after
not appropriate for a general purpose scene graph.   You'll need to
work out how to build each of the components necessary yourself, it's
very much as task in the domain of your application.  I'm afraid this
is not an trivial task, it's not something I'd expect a developer new
to scene graphs and vector maths to try and tackle so you may have a
steep learning curve ahead if you want to tackle it yourself.

Much of this learning isn't OSG specific, the OSG is only relevant to
storage of data, computation of what parts of the scene graph are
relevant and the maths you want to use will all be down to you and
tailored to your applications needs.

>And how can I get longitude,latitude and altitude for the points(say 
> point1).? Is there any example for this.? So that it can be helpful for me.

The way you typically do this type of task is to transform local
vertices of geometries into world coordinates which is typically. ECEF
(Earth Center Earth Fixed) for whole earth databases, then use the
osg::ElipsoidModel to compute the world coords into lats and longs.  I
don't recall any specific example code that does this. the headers to
EllispodModel has all that you need at the low level of the
conversion.

> Do I need to build any other OSG application for this task.?   Where does the 
> longitude,latitude and altitude informations are stored in 3d models 
> (.3ds,.osg,.osgt)?

Lat, long and altitude are not generally stored in subgraphs of a
scene graph, instead the subgraphs have their own local coordinate
frames or may be stored in world coodinates. The only place where
lat,longs and altitude come in are implicitly via the EllipsoidModel
attached to a CoordinateSystemNode that can be used to decorate a
scene graph.  Typically only whole earth models will have
CoordinateSystemNode.  You always have to compute the lat, long and
altitude for individual points on demand as they aren't stored, only
the local/word coordinates are stored in the scene graph.

Robert.
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Re: [osg-users] calculating area of the 3d model.

[Sebastian Messerschmidt]

Hi Uma

Hi all,

 I would like to know some information.

 I need to calculate area , perimeter & volume of a selected part or area 
in 3d model. For example after rendering 3d model, if I select some area(cloased 
area) , say point1 point2 point3. Point1 connected to point2 point2 to point3, 
point3 connected to point1. Is it possible to do it with the help of OSG.?
There might be some helper functions, but basically perimeter and area 
need some adjacency information, so I guess you need to do some 
additional work.


   And how can I get longitude,latitude and altitude for the points(say 
point1).? Is there any example for this.? So that it can be helpful for me.
That doesn't make sense really if your "points" are not ECEF. Basically 
you can use the osg::CoordinateSystemNode and the projection to convert 
geographic and geocentric coordinates.


In order to transform a local mesh to a specific lat-lon position you 
need to orient the model at the local tangent plane (you can get the 
matrix from the CoordinateSystemNode (set up with the ellipsoidmodell):


osg::CoordinateSystemNode* csn = new osg::CoordinateSystemNode();
csn->setEllipsoidModel(new osg::EllipsoidModel());
osg::Matrixd local_frame = 
csn->computeLocalCoordinateFrame(position);

For orientation simply rotate your model by the local_frame, where the 
position is ECEF. You can obtain an ECEF-position relative to the chosen 
Ellipsoid by using the 
Ellipsoid::computeLocalToWorldTransformFromLatLongHeight function.








Do I need to build any other OSG application for this task.?  Where does the 
longitude,latitude and altitude informations are stored in 3d models 
(.3ds,.osg,.osgt)?
There is no fixed coordinate system in the files/OSG. The coordinates 
are simply numbers in an (orthonormal) coordinate frame. So it is up to 
you to interpret them as being angles, meters, microfortnights or whatever.


Cheers
Sebastian




...

Thank you!

Cheers,
Uma

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[osg-users] calculating area of the 3d model.

[Uma Devi Selvaraj]

Hi all,

 I would like to know some information.
 
 I need to calculate area , perimeter & volume of a selected part or area 
in 3d model. For example after rendering 3d model, if I select some 
area(cloased area) , say point1 point2 point3. Point1 connected to point2 
point2 to point3, point3 connected to point1. Is it possible to do it with the 
help of OSG.?

   And how can I get longitude,latitude and altitude for the points(say 
point1).? Is there any example for this.? So that it can be helpful for me.

Do I need to build any other OSG application for this task.?  Where does the 
longitude,latitude and altitude informations are stored in 3d models 
(.3ds,.osg,.osgt)?
 


... 

Thank you!

Cheers,
Uma

--
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http://forum.openscenegraph.org/viewtopic.php?p=69400#69400





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