The VXL Project

On Sun 09 Oct 2005, BRIDGE HUANG wrote:
> I am trying to cross compile vxl for arm9 platform.
> The compiler is cross gcc 3.4.4, os - Redhat linux 9, and kernel 2.4.18-14.
>  The outputs when building vnl_math.o of ARM-VERSION are:
>  /home/ARMDevelop/vxl-1.2.0/vxl-arm-src/core/vnl/vnl_math.cxx: In function
> `bool vnl_math_isfinite(long double)':
> /home/ARMDevelop/vxl-1.2.0/vxl-arm-src/core/vnl/vnl_math.cxx:198: error:
> `finitel' undeclared (first use this function)
[...]

My guess is that the auto-generated "system and compiler capabilities"
are for the host platform instead of the target platform. Are you
using CMake to compile? As I understand it, CMake currently does not
support cross-compiling.

 As part of the configuration process, vxl determines the capabilities
of your compiler and of your system libraries. The results of these
tests are stored in two sets of files in your *binary* tree:
1.  vcl/vcl_config_compiler.h, vcl_config_headers.h,
    vcl_config_manual.h
2.  core/vxl_config.h

You can edit these header files by hand to match the capabilities of
the target system. For the errors you mentioned, have a look at the
various *FINITE* settings in core/vxl_config.h.

Amitha.

vgl has an elegant alogithm that computes the point on the conic closest
to a given point. Anyone knows of a reference to that (paper/book)?

algo/vgl_homg_operators_2d.txx:

//: Return the point on the conic closest to the given point
template <class T>
vgl_homg_point_2d<T>
vgl_homg_operators_2d<T>::closest_point(vgl_conic<T> const& c,
                                        vgl_homg_point_2d<T> const& pt)


Thanks,

osama

> vgl has an elegant alogithm that computes the point on the conic
> closest to a given point.
> Anyone knows of a reference to that (paper/book)?

As the in-source documentation states, this is standard plane
projective geometry:

"The nearest point must have a polar line which is orthogonal to its
 connection line with the given point; all points with this property
 form a conic."

You can find theory and applications of polar points and lines in any
text book on projective geometry.
The actual implementation in vgl was not borrowed from any such text
book: I just implemented it based on the ideas of polar line/point, and
using the algorithm to intersect two conics.
(By the way, that intersection algorithm is also a straightforward
consequence of standard projective geometry, viz. bundles of conics.)

--	Peter.

Any particular reason the intersection of two conics operator returns only
real solutions? It seems limiting conisering that a lot of the projective
geometry algorithms depend on complex solutions (e.g., every two circles
intersect at the circular points [1 i 0] and [1 -i 0]). Since the class is
templated, one idea would be that if the return type is vcl_complex,
complex solutions are returned as well.

-osama

On Wed, 12 Oct 2005, Peter Vanroose wrote:

> > vgl has an elegant alogithm that computes the point on the conic
> > closest to a given point.
> > Anyone knows of a reference to that (paper/book)?
>
> As the in-source documentation states, this is standard plane
> projective geometry:
>
> "The nearest point must have a polar line which is orthogonal to its
>  connection line with the given point; all points with this property
>  form a conic."
>
> You can find theory and applications of polar points and lines in any
> text book on projective geometry.
> The actual implementation in vgl was not borrowed from any such text
> book: I just implemented it based on the ideas of polar line/point, and
> using the algorithm to intersect two conics.
> (By the way, that intersection algorithm is also a straightforward
> consequence of standard projective geometry, viz. bundles of conics.)
>
> --	Peter.
>

> Since the class is templated, one idea would be that if the
> return type is vcl_complex, complex solutions are returned as well.

Good idea!


--	Peter.