You do raise the issue as to whether or not there should be tolerances
in other vgl functions that have to make a bool decision. We should be
uniform in this regard. Maybe there should be a global constant class
defined, e.g. vgl_tolerance<T> with different static values, such as
It would only take a few of these tolerances to cover most of the
geometric predicates needed for vgl.
From: Kieran O'Mahony [mailto:kieranom@...]
Sent: Thursday, August 16, 2007 10:56 AM
To: Joseph Mundy
Subject: Re: [Vxl-maintainers] vgl_point_3d eps test
Just to be clear, I would like to introduce the eps test in the body
of the function and avoid introducing any argument (default or
On 16/08/07, Kieran O'Mahony <kieranom@...> wrote:
> Unfortunately, in order to be usable introducing an argument with a
> default value (presumably defaulting to 0) would require the
> introduction of default values in other vgl functions which use
> vgl_point_3d's coplanar function e.g. functions in vgl_intersection
> and vgl_line_3d_2_points.
> Introducing changes in these functions would probably suggest that a
> lot of vgl functions should be updated with default eps arguments
> However a more serious issue if default eps arguments were introduced
> would be their compatability between functions.
> For example if a vgl_intersection function required an eps check of
> sqrt_eps say but vgl_point_3d coplanar should only be checking against
> eps directly then it is undesirable for vgl_intersection to pass on
> its eps argument to vgl_point_3d.
> Therefore I would like to avoid introducing a default argument. Hope
> this makes sense.
> On 16/08/07, Joseph Mundy <mundy@...> wrote:
> > Sounds like a good idea to me. What about a default value for
> > Joe
> > -----Original Message-----
> > From: vxl-maintainers-bounces@...
> > [mailto:vxl-maintainers-bounces@...] On Behalf Of
> > Kieran O'Mahony
> > Sent: Thursday, August 16, 2007 8:38 AM
> > To: vxl-maintainers@...
> > Subject: [Vxl-maintainers] vgl_point_3d eps test
> > Hi all,
> > I am currently working with Ian Scott and as part of my work I am
> > dealing quite a bit with parts of vxl but mainly vgl.
> > Something that has cropped up recently is the lack of an eps test in
> > the vgl_point_3d coplanar() function. At present the decision is
> > on a direct equality check with zero. Would anyone object to
> > this with a bounds check around zero using
> > vcl_numeric_limits<Type>::epsilon() ?
> > This should be fine for all possible template types as according to
> > the C++ standard epsilon() should return 0 for any types where it
> > doesn't make sense (integer etc).
> > BTW I also noticed a couple of sign mistakes in the same function
> > have corrected them.
> > Thanks,
> > Kieran
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