Re: [osg-users] LineSegmentIntersector gives incorrect results (intersections missing)
Hi Jaap, In svn/trunk I've introduced the ability to set the Eplsion value to a user specified value rather than the default of 1e-4, this may not be an ideal solution though, I'd much rather have the code work with defaults correctly. The clipping of the line length to the bounding box is done to make it more likely that intersection tests will be more rejected more quickly so speeding up the intersections. We could add an option to disable this clipping and explore just much of an impact it has. Scaling the epsilion by the size of the bounding box is a possibility, but this would cause problems with small objects but with relatively large xyz values. One could possible have a constant and scaled epsilon term to get round this. A double version of the intersection functions wold be another possibility. Robert. On 16 May 2013 09:07, Jaap Glas jaap.g...@dgbes.com wrote: Dear Peter, Robert, and all. I would like to endorse Peter's remarks on the current implementation of the LineSegmentIntersector. We experience precisely the same problems when trying to pick on plane faces that coincide with the bounding box of the Drawable to which they belong. The simplest example is a drawable consisting of one triangle or quad aligning with the axes of the local coordinate frame. Like Peter, we are also dealing with co-ordinate values running into the thousands. The applied epsilon of 1e-4 in the intersectAndClip() function is too small in suchlike cases, especially if the TriangleIntersector keeps using floats at some places. For the moment, we circumvent the problem by overloading the computeBound() function of the Drawable and return a slightly bigger bounding box ourselves, but a more general solution would be better in the end. Like Peter, I also do not see why the intersectAndClip() function should cut off those parts of the line segment that are outside the bounding box. What is the computational benefit of this later on? I would expect it is sufficient to check whether the line segment is crossing the box or not, and neglect Drawables for which the answer is false. However, assuming that this clipping does serve a goal, then my choice would be not to assign the epsilon in the intersectAndClip() function an absolute value, but to make it relative to the bounding box size, for example by multiplying the current epsilon of 1e-4 with the diagonal length of the bounding box. Best regards, Jaap Glas dGB Earth Sciences Enschede, The Netherlands -- Read this topic online here: http://forum.openscenegraph.org/viewtopic.php?p=54027#54027 ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] LineSegmentIntersector gives incorrect results (intersections missing)
Dear Peter, Robert, and all. I would like to endorse Peter's remarks on the current implementation of the LineSegmentIntersector. We experience precisely the same problems when trying to pick on plane faces that coincide with the bounding box of the Drawable to which they belong. The simplest example is a drawable consisting of one triangle or quad aligning with the axes of the local coordinate frame. Like Peter, we are also dealing with co-ordinate values running into the thousands. The applied epsilon of 1e-4 in the intersectAndClip() function is too small in suchlike cases, especially if the TriangleIntersector keeps using floats at some places. For the moment, we circumvent the problem by overloading the computeBound() function of the Drawable and return a slightly bigger bounding box ourselves, but a more general solution would be better in the end. Like Peter, I also do not see why the intersectAndClip() function should cut off those parts of the line segment that are outside the bounding box. What is the computational benefit of this later on? I would expect it is sufficient to check whether the line segment is crossing the box or not, and neglect Drawables for which the answer is false. However, assuming that this clipping does serve a goal, then my choice would be not to assign the epsilon in the intersectAndClip() function an absolute value, but to make it relative to the bounding box size, for example by multiplying the current epsilon of 1e-4 with the diagonal length of the bounding box. Best regards, Jaap Glas dGB Earth Sciences Enschede, The Netherlands -- Read this topic online here: http://forum.openscenegraph.org/viewtopic.php?p=54027#54027 ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] LineSegmentIntersector gives incorrect results (intersections missing)
Hello Robert. I digged a bit into the OSG source code and I found out that its a precision problem. I use big models where the vertex coordinate values are 1000. I don't know the exact process of the intersection search, but I assume that the lineSegment is clipped in the lineSegmentIntersector.cpp Code: bool LineSegmentIntersector::intersectAndClip(osg::Vec3d s, osg::Vec3d e,const osg::BoundingBox bbInput) function to the values, where the lineSegment is slightly longer, than the bounding sphere of the geometry. Code: osg::Vec3d bb_min(bbInput._min); osg::Vec3d bb_max(bbInput._max); #if 1 double epsilon = 1e-4; bb_min.x() -= epsilon; bb_min.y() -= epsilon; bb_min.z() -= epsilon; bb_max.x() += epsilon; bb_max.y() += epsilon; bb_max.z() += epsilon; #endif There is an epsilon value, which is currently set to 1e-4. I would suggest to set it bigger (1e-2 f. ex.). If I change it to 1e-2, I don't get this problem anymore. What is the exact reason of lineSegment clipping? Thank you! Cheers, Peter Code: -- Read this topic online here: http://forum.openscenegraph.org/viewtopic.php?p=51119#51119 ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] LineSegmentIntersector gives incorrect results (intersections missing)
HI Peter, I'm afraid I've not got enough time available to look into this problem right now, hopefully others can dive in. My suspicision is that due to nuermical precision issues on constructing the linesegment and/or intersecting this with the bonding volumes or meshes you aren't always getting the intersections you expect. A quick hack to test this would be to rotate the mesh slightly so nothing is axis aligned - this way the mesh won't be setting on the face of the bounding volume. If this hack does prove to address the problem then it points the need of doing interesection testing with error bars that are larger than the numberic precision errors. Robert. On 23 October 2012 09:21, Peter Bako osgfo...@tevs.eu wrote: I use the LineSegmentIntersector in my application to select planar faces. The problem is that sometimes when I click on the face facing to you (check the red Xes on the picture), I get no intersection of this face. I get only an intersection on the face which is not visible from this view - the bottom face. Then sometimes it happens, that the user wants to select a face, but an invisible face is selected instead, but he doesn't know it because he doesn't see it, even if its highlighted. i made this sample application to simulate my problem - when I click on the positions where the red crosses are, normally I should get 2 intersections - first the face where I drew the red crosses and then to bottom face which we don't see. Sometimes, I get only the second (see the debug output on the picture). I think this is a problem. Thank you! Cheers, Peter -- Read this topic online here: http://forum.openscenegraph.org/viewtopic.php?p=50727#50727 ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] LineSegmentIntersector gives incorrect results (intersections missing)
I use the LineSegmentIntersector in my application to select planar faces. The problem is that sometimes when I click on the face facing to you (check the red Xes on the picture), I get no intersection of this face. I get only an intersection on the face which is not visible from this view - the bottom face. Then sometimes it happens, that the user wants to select a face, but an invisible face is selected instead, but he doesn't know it because he doesn't see it, even if its highlighted. i made this sample application to simulate my problem - when I click on the positions where the red crosses are, normally I should get 2 intersections - first the face where I drew the red crosses and then to bottom face which we don't see. Sometimes, I get only the second (see the debug output on the picture). I think this is a problem. Thank you! Cheers, Peter -- Read this topic online here: http://forum.openscenegraph.org/viewtopic.php?p=50727#50727 ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] LineSegmentIntersector gives incorrect results (intersections missing)
Hi Peter,
I can't specifically say what you are seeing a problem, but it does
rather sound like a precision issue with projecting the mouse poistion
into clip space and then to world and final object coordinates.
Robert.
On 17 October 2012 14:19, Peter Bako osgfo...@tevs.eu wrote:
Hi,
I've got a problem with line segment intersector. Sometimes I get only one
intersection (on the bootom side of the table), while I should get two.
Please check the screenshot.
Do you have any idea why this happens? What should I do?
STLFILE.stl (ZIPPED) is attached
Thank you!
Cheers,
Peter
Hold CTRL key to activate intersection output.
This is the code I use:
Code:
#include stdafx.h
#include osgViewer/Viewer
#include osgDB/ReadFile
#include osgUtil/LineSegmentIntersector
class PickHandler : public osgGA::GUIEventHandler
{
public:
virtual bool handle( const osgGA::GUIEventAdapter ea,
osgGA::GUIActionAdapter aa )
{
if ( ea.getEventType()!=osgGA::GUIEventAdapter::RELEASE ||
ea.getButton()!=osgGA::GUIEventAdapter::LEFT_MOUSE_BUTTON ||
!(ea.getModKeyMask()osgGA::GUIEventAdapter::MODKEY_CTRL) )
return false;
osgViewer::Viewer* viewer = dynamic_castosgViewer::Viewer*(aa);
if ( viewer ){
osg::ref_ptrosgUtil::LineSegmentIntersector intersector =
new
osgUtil::LineSegmentIntersector(osgUtil::Intersector::WINDOW, ea.getX(),
ea.getY());
osgUtil::IntersectionVisitor iv( intersector.get() );
iv.setTraversalMask( ~0x1 );
viewer-getCamera()-accept( iv );
if ( intersector-containsIntersections() ){
const
osgUtil::LineSegmentIntersector::Intersection result =
*(intersector-getIntersections().begin());
printf(Intersection count:%d. Coordinates: %.2f, %.2f,
%.2f\n,
intersector-getIntersections().size(),
result.getWorldIntersectPoint().x(),result.getWorldIntersectPoint().y(),result.getWorldIntersectPoint().z());
}
}
return false;
}
};
int main( int argc, char** argv )
{
osg::ref_ptrosg::Node model1 = osgDB::readNodeFile( STLFILE.stl );
osg::ref_ptrosg::Group root = new osg::Group;
root-addChild( model1.get() );
osg::ref_ptrPickHandler picker = new PickHandler;
osgViewer::Viewer viewer;
viewer.setSceneData( root.get() );
viewer.addEventHandler( picker.get() );
return viewer.run();
}
--
Read this topic online here:
http://forum.openscenegraph.org/viewtopic.php?p=50644#50644
Attachments:
http://forum.openscenegraph.org//files/intersection_errors_639.png
http://forum.openscenegraph.org//files/stlfile_974.zip
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[osg-users] LineSegmentIntersector gives incorrect results (intersections missing)
Hi,
I've got a problem with line segment intersector. Sometimes I get only one
intersection (on the bootom side of the table), while I should get two.
Please check the screenshot.
Do you have any idea why this happens? What should I do?
STLFILE.stl (ZIPPED) is attached
Thank you!
Cheers,
Peter
Hold CTRL key to activate intersection output.
This is the code I use:
Code:
#include stdafx.h
#include osgViewer/Viewer
#include osgDB/ReadFile
#include osgUtil/LineSegmentIntersector
class PickHandler : public osgGA::GUIEventHandler
{
public:
virtual bool handle( const osgGA::GUIEventAdapter ea,
osgGA::GUIActionAdapter aa )
{
if ( ea.getEventType()!=osgGA::GUIEventAdapter::RELEASE ||
ea.getButton()!=osgGA::GUIEventAdapter::LEFT_MOUSE_BUTTON ||
!(ea.getModKeyMask()osgGA::GUIEventAdapter::MODKEY_CTRL) )
return false;
osgViewer::Viewer* viewer = dynamic_castosgViewer::Viewer*(aa);
if ( viewer ){
osg::ref_ptrosgUtil::LineSegmentIntersector intersector =
new
osgUtil::LineSegmentIntersector(osgUtil::Intersector::WINDOW, ea.getX(),
ea.getY());
osgUtil::IntersectionVisitor iv( intersector.get() );
iv.setTraversalMask( ~0x1 );
viewer-getCamera()-accept( iv );
if ( intersector-containsIntersections() ){
const
osgUtil::LineSegmentIntersector::Intersection result =
*(intersector-getIntersections().begin());
printf(Intersection count:%d. Coordinates: %.2f, %.2f,
%.2f\n,
intersector-getIntersections().size(),
result.getWorldIntersectPoint().x(),result.getWorldIntersectPoint().y(),result.getWorldIntersectPoint().z());
}
}
return false;
}
};
int main( int argc, char** argv )
{
osg::ref_ptrosg::Node model1 = osgDB::readNodeFile( STLFILE.stl );
osg::ref_ptrosg::Group root = new osg::Group;
root-addChild( model1.get() );
osg::ref_ptrPickHandler picker = new PickHandler;
osgViewer::Viewer viewer;
viewer.setSceneData( root.get() );
viewer.addEventHandler( picker.get() );
return viewer.run();
}
--
Read this topic online here:
http://forum.openscenegraph.org/viewtopic.php?p=50644#50644
Attachments:
http://forum.openscenegraph.org//files/intersection_errors_639.png
http://forum.openscenegraph.org//files/stlfile_974.zip
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