[GRASS-dev] Zooming issue in gis manager

Michael Barton michael.barton at asu.edu
Wed Nov 1 14:15:06 EST 2006

To clarify a bit...

In the "standard" mode, resolution and geometry are preserved by the display
in all zooming. In fact, there is no way to change resolution in this mode,
although you can interactively change the size and shape of a display region
by zooming in or out.

In the "explore" mode that Cedric Shock introduced, neither geometry nor
resolution is preserved in the display in order to provide quick,
full-screen views of maps. The display resolution changes to keep it
proportional to the number of pixels and the map always fills the display.

Users can switch back and forth between modes with the click of a button.

In all cases, display resolution and geometry have no effects at all on
computational geometry or region, although settings from the display region
can be copied to the computational region and vice versa if the users wants
to do so.

Michael Barton, Professor of Anthropology
School of Human Evolution & Social Change
Center for Social Dynamics and Complexity
Arizona State University

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton

> From: Maciej Sieczka <tutey at o2.pl>
> Date: Wed, 01 Nov 2006 16:47:05 +0100
> To: Glynn Clements <glynn at gclements.plus.com>
> Cc: Michael Barton <michael.barton at asu.edu>, grass-dev
> <grass-dev at grass.itc.it>
> Subject: Re: [GRASS-dev] Zooming issue in gis manager
> Michael Barton wrote:
>> This sounds like there is no good reason to set this for interactive zooming
>> by default. If someone wants to use this feature, they could explicitly set
>> it in g.region.
> Glynn,
> gis.m zoom tools should preserve the resolution while zooming, and set
> the region extents properly. That's because there are tools in gis.m to
> set WIND to match gis.m display, and to make the display match the
> current region - thus these two operations should not lead to region or
> display settings the user not wanted. The problem is that they do, because:
> 1. If -a is not used in g.region calls in mapcanvas.tcl (like it was
> originally, few months ago), the gis.m zoom tools don't preserve the
> resolution while zooming; and I don't see a reason why the resolution
> should change while zooming, but do I see obvious reason why it
> shouldn't. Thus, I suggested a solution: use the g.region with -a. It
> fixed the resolution issue.
> 2. But, now it showed that if g.region -a is used in mapcanvas.tcl, the
> region extent is often not set properly. This is not acceptable either,
> is it?
> Removing the -a flag should fix issue 2, but it will bring the issue 1
> back. What do we do then?
> Maciek

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