Re: [Boost-users] [boost::polygon::transform.hpp] Concatenation of transformations fails.

Simonson, Lucanus J 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& transformation::operator+=(const transformation& 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 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

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

code below:

template <typename coordinate_type> inline const transformation& transformation::operator+=(const

all my geometry data objects properly with the fixed transformation& 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 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

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

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

release. You'll note that I'm still transformation object to have a 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