qwtplot3d-interest

Why is plot shifting limited to [-1..1] and is there a workaround?

[Adam G. <ag...@in...>]

I am writing a program that allows a user to view terrain in 3D. I am
using a derivative of Plot3D, which uses the built-in ability to shift
(pan) the view. The Plot3D::setViewportShift(), which handles the
shifting, function states that the function "Performs shifting along
screen axes. The values are limited to the interval [-1..1]. The shift
moves points inside a sphere, which encloses the unscaled and unzoomed
data by multiples of the spheres diameter."=20

=20

When shifting a view that has not been zoomed, this works great.
However, if the user zooms in on the view and then attempts to shift,
they hit an invisible "wall" when trying to shift to the end of the
zoomed view because the Plot3D::setViewportShift() does not take zooming
into effect a limits the shifting from -1 to 1. The result is the
inability to view some portions of the terrain when zoomed in because
the shift prevents shifting far enough to see it. This is easy to
reproduce: Load up the mesh2 example, zoom in on one of the shapes and
then attempt to shift it off the screen. It won't work because of this
limitation.

=20

Is there a reason that this [-1..1] limitation is in effect? Is there a
way to workaround this so that I can allow users to see all parts of the
terrain when zoomed in by shifting? Any help would be much appreciated.
Thank you.

Re: Why is plot shifting limited to [-1..1] and is there a workaround?

[Micha B. <kri...@us...>]

Thursday, August 25, 2005, 18:52:56, Adam Gurson wrote:

> When shifting a view that has not been zoomed, this works great.
> However, if the user zooms in on the view and then attempts to shift,
> they hit an invisible "wall" when trying to shift to the end of the

I have to admit, this error is a 'skeleton in my closet'. It's very
probably fixed for version 0.2.6 (Qt 4.0.1 adaption, release next
weekend).
I'll give you a hint, if the change makes it into cvs beforehand.

Micha

Re: Why is plot shifting limited to [-1..1] and is there a workaround?

[Micha B. <kri...@us...>]

Adam,

please look for

qwt3d_movements.cpp:
void Plot3D::setViewportShift( double xVal, double yVal )

and change the 'limit' variable to something larger (or remove them and
the related if-statements completely). The parameter creates the
mentioned 'wall'. To be honest, I cannot remember exactly what in the
past the reason for introducing the limitation was ..
Caused by a more unpleasing old error, the release for version 0.2.6
might be on hold for a few days, but I'll eventually move the change
into the final version too.

Micha  
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