====== ORIGINAL POST ======
At 12:43 AM 07-06-02, you wrote:

Chris, I have been looking more closely at the different systems
available in TAL and am a little confused with the French Aisne
system.
Going on your standard of X being sand and Y being clay (as defined in
'how to define your own scheme'), in the following polygon for 'sable'
(which I take to be 'sand') a sample with 5% sand and 95% clay would
actually come out as sand!

sable
15
0 87.5
0 100
20 80
7.5 80
#

Does the 3rd line in the dat file

(x, y, z): (limons 0.002-0.05, sables 0.05-2.0, argile <0.002)

imply that the x axis is actually silt, the y axis is sand and the z
clay? Most other systems seem to work on your standard of X being sand
and Y being clay. This seems to be the only way I can get it to make
sense.



====== REPLY ======
Hi,

Though I have never used the French scheme before, the scheme
definition file TAL uses was based *exactly* on a chart I got from a
soil textbook by a French author who, in turn, got it from a French
journal as stated in the scheme info.

To answer your question, the line of "(x, y, z): (limons
0.002-0.05, sables 0.05-2.0, argile <0.002)" in the Aisne scheme file
means that x, y and z axes are silt, sand and clay, respectively.
This order can change according to the scheme type but for most
schemes (including USDA and UK), the order is usually sand, clay and
silt, respectively. I have looked at several schemes, and yes, the
meaning of the x, y and z axes are not "standardised" and they can
vary from scheme to scheme. You can also look at the INEAC scheme --
very surprising!

In short, the meaning of the x, y and z axes for a particular
classification scheme are based exactly on the soil charts I have
found; I have not re-orientated the axes so they conform to the
standard of x axis always being the sand and y axis the clay.

I hope this helps.

Best wishes
Chris