Re: Pick and [Update REQ 6232]: Geomview

[R.Wardle at sheffield.ac.uk]

Hello,

I have some further info to this message I sent earlier this week.


On Mon, 7 Jul 1997 R.Wardle at sheffield.ac.uk wrote:

> Date: Mon, 7 Jul 1997 16:20:50 +0100 (BST)
> From: R Wardle <R.Wardle at sheffield.ac.uk>
> To: software@geom.umn.edu
> Subject: Pick and [Update REQ 6232]: Geomview
> Message-ID: <Pine.SGI.3.94.970707160555.24681B-100000 at silver.shef.ac.uk>
> 
> Hello,
> 
> Thanks for replying to my previous request (REQ 6232) - I have sucessfully
> dealt with this now. I have a related question now, concerning the pick
> command in gcl. Using Nose with even relatively simple polyhedra I have
> difficulty in picking the exact face - sometimes I pick the edge instead
> of the face, even when the mouse pointer is nowhere near the edge. Some
> faces seem to be almost impossible to pick, too, even though I have
> enlarged the Camera window to the full size of my screen. In case this is
> a hardware thing, I am using a Sun Sparc 4, Solaris 2.4, 15" monitor (I'm
> not sure what the video adapter is, but it is whatever Sun ship with the
> Sparc 4). I compiled the program myself.
> 
> Is this a recognised problem with Geomview? The picking behaviour as a
> whole seems to have an element of randomness about it.
> 


The pick mechanism seems regularly to detect edges, or rather the
extensions of edges. For instance, I was viewing the
rhombicosidodecahedron and often when I tried to select one of the small
square faces using Nose I would instead select a point on the extension of
an edge formed from the intersection of two of the surrounding faces; i.e.
if you produced the edges leading into the corners of the square face, you
would get four produced lines crossing perpendicularly above the centre
of the square face. These `virtual lines' are what I seemed to be
selecting a large part of the time.

Is this a problem with the pick mechanism? I've even managed to select
produced edges that do not joint to the face I'm trying to pick, which
puts the little Nose pick box clearly in mid air above the face I'm trying
to pick, but evidently on the produced edge which is highlighted by Nose.


Thanks for your attention and help again,

Robin.


--
Robin Wardle <r.wardle at sheffield.ac.uk>
Dynamics Research Group, Department of Mechanical Engineering,
Mappin Building, Mappin Street, University of Sheffield, UK
tel: (0114) 22 27760   ...   fax: (0114) 275 3671