[Maths-Education] dynamic geomertry software

[Dave Wilson]

Peter Gates wrote:
>
>Colleagues - I'm after advice.
>
>I am looking to purchase a Dynamic geometry package for use with out PGCE
>ITE students. This is not my immediate area of expertise so i have a
>question...
>
>
>Should I buy a licence for Cabri or for Geometer's sketchpad - or for what?
>
>Which is preferable, which is 'bette'r whatever that means?
>
How should i chose?


Before I start, I suppose that I ought to say what I usually say - 
broadly they both do the same thing and have much the same 
functionality, so you buy the one whose user interface you prefer.

However;

You'll find considerable discussion about the UI's on the dynamic 
geometry discussion list (see
http://forum.swarthmore.edu  follow the Discussion Groups link) GSP 
insists you select the objects needed as a basis for a construction 
and then the tool (angle bisector, say), whereas Cabri reverses this 
- GSP, apparently follows the usual methods in wordprocessors and 
drawing packages. I think that the argument that this is better 
because more standard is misleading. Cabri seems to me to echo how 
people think geometry.

Cabri gives feedback to the user around the pointer (as the mouse 
passes near a point a tag appears saying 'this point') - GSP provides 
similar feedback in an area at the bottom of the window, precisely 
the wrong place it seems to me.

GSP provides a 'snap to grid' menu command which snaps points to 
lattice points on a grid - Cabri allows you to construct points lying 
on lattice points. Cabri is a defined constraint - with GSP if you 
change the grid size by dragging the snapped points do not move with 
the grid, and you then have to re-snap.  This is an example of an 
underlying difference which I want to express by saying that Cabri is 
more 'geometrical' than GSP.

I would need to look at GSP to check this out, but Cabri's locus tool 
is richer - an extra basic tool is a conic defined by 5 points 
(though I guess we don't need this much in secondary - but it is 
wonderfully useful when looking at parabolas and linking to 
coordinate graphing).
Are Cabri's set of axes more user definable than GSP - they can be at 
any angle, different unit spacing?

Both have added a very useful functionality - you can use Java to 
view figures constructed in Cabri/GSP within a web browser - CAbri 
has implemented this in a far more efficient manner, I think.

What else?

Oh, yeah macros (Cabri) and scripts (GSP). I hate and loathe GSP's 
scripts. Both actually offer much the same functionality and power, 
but ..

(preamble - these are ways of adding frequently used, demanded 
constructions or ones which a teacher wishes to provide for their 
students - eg I can provide a group with a 'circumcircle' tool 
operating on 3 points, or a tool for the radical axis of a pair of 
circles, or whatever)

Cabri user defined macros appear along with the built-in tools in the 
button bar and are used in exactly the same manner GSP's are scripts, 
distinct from the rest of the tools and need to be 'RUN'
Cabri macros when invoked only produce in the figure the defined 
output object/s (a circle around points - GSP scripts when invoked 
quickly spin through the full construction 
(mid-points/perpendiculars/intersecting point/circle then hide the 
construction details if the user has selectd that) but the underlying 
details are present in the figure, albeit 'hidden' and can be viewed, 
the producer of the GSP sketch has no choice over this, The Cabri 
producer has a choice. This means that Cabri can be used to produce 
very clean figures with almost no 'hidden' construction details if 
that is what you want - GSP sketches quickly become a scab of hidden 
opbjects which loses the power of revealing the structure of a 
construction. GSp loses sense of synthesis to the user of a  sketch, 
you see everything rather than being able to see higher level 
structure.


GSP does have a useful set of additions - buttons which allow the 
producer to place buttons on the screen which do things - eg hide or 
show a set of objects (this can help with the scripts issue above), 
or animate a point or all sorts of things. This is powerful as a way 
of producing a sketch which is easily manipulable without needing to 
know how to use GSP or any geometry!
Cabri can do all these things (almost), but the producer needs to use 
some slightly clever geometrical constructions so that sliding a 
point along a segment 'switches' a construction on and off.

Finally, GSP on a Mac can save an animated sketch as a Quicktime 
movie - clever and nice, self contained. Cabri I think can be 
persuaded to do this using 3rd party software (Cameraman?)

Clearly, I think that Cabri is much the superior and I use both. We 
have a site licence for Cabri of course!

Download the demos from the websites -
http://www.cabri.net
http://www.keypress.com

look at the forum (URL above) discussion lists you can search their archives.
Use the demos to look a the ATM Active Geometry software, but don't 
be misled by these - I think that Cabri/GSp are precisely the wrong 
media to produce such files - they should have been programmed.
There are many websites with examples of Cabri and GSP figures to 
visit, including ours here,


I hope some of the above helps - I have just splurged stuff, I'm afraid, Peter!


cheers
-- 
Dave
Dave Wilson  (D.Wilson@mmu.ac.uk     A letter always reaches its 
destination                 Dave@zizek.demon.co.uk)              Lacan
http://s13a.math.aca.mmu.ac.uk