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

[Robert Osfield]

On 16 November 2016 at 13:21, Uma Devi Selvaraj <umaselvam1503 at gmail.com> 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.