[GRASSLIST:10282] Re: [GRASS5] New release candidate 3 of GIS Manager 2

Michael Barton michael.barton at asu.edu
Tue Feb 14 02:01:56 EST 2006

A couple things to think about on the deceptively simple, but important task
of zooming.

The most frequent way of zooming I've encountered in GIS and graphic
programs is the way it was set up in the previous release of gism--

-select zoom
-draw zoom rectangle
-map zooms to that rectangle

This is the way that most people unused to GRASS would expect it to work.

The 3-button zoom in d.zoom can be very convenient...once you get used to it
and if you're sitting at a nice desktop workstation with a 3-button mouse.

If you have a Mac with a 1-button mouse (the norm until very recently) or PC
with a 2-button mouse (the norm until recently) or a laptop with a 1 or
2-button trackpad (still the norm), the 3-button zoom is a real pain. It
means that you have to always use 2 hands and key combinations to do a
simple zoom.

In most graphic programs (perhaps CAD excepted), if you select a line tool,
it is only selected until you have completed the line. It does not stay
selected to allow you to keep drawing lines. Again, this is commonly
expected behavior because it is the way that may graphic programs work.

Likewise, zoom-out rectangles are standard on other GIS programs and some
other graphic programs.

By following common tool behavior, you shorten the learning curve for new

Of course, the 'normal' way a tool behaves may not be the best way it could
behave (QWERTY keyboards are one of the better known examples of this).

On the other hand, what is convenient for some may not be for others. The
old d.zoom had multiple kinds of display manipulation built into a single
tool--zoom in by rectangle, zoom out by set amounts, and pan. Sometimes I
found this very handy, other times very cumbersome. Most people unused to
GRASS were baffled by it for awhile at least. GIS software and concepts are
complicated enough, without adding unnecessary bafflement.

So what to do? My goal, at least is to try to make tools easier AND more
functional. These are sometimes conflicting goals (ignoring any programming

Because zooming seems to be a hot button issue (pun intended) with responses
from various sides of the fence, it's one that deserves more thought about
how to do it better (easier and more functional) within the limits of the
interface software.

I appreciate your comments and those of others on this subject.
Suggestions--and programming help--are also appreciated.

Michael Barton, Professor of Anthropology
School of Human Evolution and Social Change
Arizona State University
Tempe, AZ 85287-2402

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

> From: William Kyngesburye <woklist at kyngchaos.com>
> Date: Mon, 13 Feb 2006 17:36:32 -0600
> To: <grass5 at grass.itc.it>, <grasslist at baylor.edu>
> Subject: [GRASSLIST:10282] Re: [GRASS5] New release candidate 3 of GIS Manager
> 2
>> let's see what response is to this one
> My response - yes for continuous zoom.  It's a tool, and one uses a
> tool until another is selected.
>>> Moreover, I don't understand why I need to select a rectangle to
>>> _unzoom_. Am I missing something? Zoom out tool should... zoom out
>>> once I click the button, why select region and confirm? Too much
>>> mouse
>>> action for no purpose, I think.
>> Zoom out rectangle give you greater control over you 'unzoom'. With a
>> zoom-out rectangle, your current map 'shrinks' to fit into the
>> rectangle. So
>> you can decide to zoom out a little (big rectangle) or a lot (small
>> rectangle). Or you can use g.region.
> I think this zoom out by rectangle thing is unintuitive.  Dragging a
> rectangle for a zoom implies getting closer, within the rectangle,
> but then you go the opposite direction.  Vertigo alert!  If you need
> a fast zoom out, is it possible to have something interrupt the
> redraw?  Then you could just click multiple times in succession.  Or
> some way to set zoom out magnitude? (could work for point-click zoom
> in also)  Either would be better.

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