Subject: Re: [Boost-users] [boost::polygon::transform.hpp] Concatenation of transformations fails.
From: Dimitris (dakopoulos_at_[hidden])
Date: 2011-08-26 04:21:18
Simonson, Lucanus J <lucanus.j.simonson <at> intel.com> writes:
>
> Dimitris Dakopoulos wrote:
> > Hello to all,
> >
> > I want to apply to geometrical transformations (in this case
> > translations) on a point.
> >
> > Point3D trans1(1,0,0);
> > Point3D trans2(2,0,0);
> >
> > Point2D p(100,100);
> >
> > gtl::transformation<int> T1( trans1 );
> > gtl::transformation<int> T2( trans2 );
> >
> > gtl::transform( p, T1 );
> > gtl::transform( p, T2 );
> >
> > --- ... and the point's coordinates are (97,100) as expected.
> >
> > --- When I try to concatenate the transformations:
> >
> > Point3D trans1(1,0,0);
> > Point3D trans2(2,0,0);
> >
> > Point2D p(100,100);
> >
> > gtl::transformation<int> T1( trans1 );
> > gtl::transformation<int> T2( trans2 );
> >
> > gtl::transform( p, T1 + T2 );
> >
> > --- ... and I get random numbers.
> >
> > I checked the boost/polygon/detail/transform_detail.hpp
> >
> > template <typename coordinate_type>
> > inline const transformation<coordinate_type>&
> > transformation<coordinate_type>::operator+=(const
> > transformation<coordinate_type>& tr){
> > //apply the inverse transformation of this to the translation
> > point of that //and convolve it with this translation point
> > coordinate_type x, y, z;
> > transformation<coordinate_type> inv = inverse();
> > inv.transform(x, y, z);
> > p_.set(HORIZONTAL, p_.get(HORIZONTAL) + x);
> > p_.set(VERTICAL, p_.get(VERTICAL) + y);
> > p_.set(PROXIMAL, p_.get(PROXIMAL) + z);
> > //concatenate axis transforms
> > atr_ += tr.atr_;
> > return *this;
> > }
> >
> > ... and I noticed that the coordinate_type x, y, z; is not initialized
> > and then the transformation is applied: inv.transform(x,y,z); which of
> > course results to something random.
> >
> > Any ideas?
> >
> > Thank you for checking.
> >
> > Dimitris
>
> Here is the fix. This function was working before I changed the interface to
all my geometry data objects
> when I "boostified" the API in 2007. Apparrently when I went through and
fixed all the code that was broken
> by that interface change I didn't properly test this function. Oddly, the
comment was also wrong because
> it didn't match the code. It would have been correct if I applied the inverse
of the axis_transformation in
> (*this), but was redundant to convolve the translation points given that
applying the full inverse
> transformation to the translation point does that already. I tested several
combinations of
> axis_transformation and translation points and everything seems to be working
properly with the fixed
> code below:
>
> template <typename coordinate_type>
> inline const transformation<coordinate_type>&
> transformation<coordinate_type>::operator+=(const
transformation<coordinate_type>& tr){
> //apply the inverse transformation of this to the translation point of
that
> coordinate_type x=tr.p_.get(HORIZONTAL), y=tr.p_.get(VERTICAL),
z=tr.p_.get(PROXIMAL);
> transformation<coordinate_type> inv = inverse();
> inv.transform(x, y, z);
> p_.set(HORIZONTAL, x);
> p_.set(VERTICAL, y);
> p_.set(PROXIMAL, z);
> //concatenate axis transforms
> atr_ += tr.atr_;
> return *this;
> }
>
> Sorry for any inconvenience. This fix should go out in the next boost
release. You'll note that I'm still
> using point_3d_data in the interface of transform, even though it is
undocumented. All the transform()
> functions that take a geometry and a tranformation object expect the
transformation object to have a
> transform member function:
>
> void transform(coordinate_type& x, coordinate_type& y) const;
>
> You can define your own transformation object types that satisfy this
requirement and you don't need to use
> mine if you don't want to. Specifically, mine are just axis transformations
with translation. For a
> general transformation you would need to declare your own that probably stores
the 2d transformation
> transformation matrix. To some extent I think of my transformation object as
example code since it isn't documented.
>
> Regards,
> Luke
>
Good morning Luke and thanks for your quick response and suggestions.
I believe I will implement my own concatenation function for the time being.
I have a probably silly question (i'm a newbie in boost)...
How can I access the point_3d_data's coordinates? I don't really buy the get()
function and it's not as simple as the point_data with the .x() and .y()
functions. .p_ are private.
In my case I want to do something like:
point_3d_data<int> trans(10,9,0);
transformation<int> T( trans );
and then for debugging purpose I want to access the coordinates but when I do:
point_3d_data<int> trans_out;
T.get_translation( trans_out );
I'm not sure what to do... trans_out.get(0) ? or trans_out.get(HORIZONTAL) ?
trans_out.get( orientation_3d(0) ) ?
I tried several but can't make it work...
Best,
Dimitris