Re: [office] surface plots

[Andreas J Guelzow <aguelzow@math.concordia.ab.ca>]

On Tue, 2009-07-28 at 17:09 +0200, Ingrid via Eike Rathke wrote:

> >>  The attribute 
> >> chart:deep has to be set to true in this case. The given values for a 
> >> series are interpreted as y-coordinates (representing the 'altitude').
> >>     
> > (As mathematician, I find it quite unusually to call the height y rather
> > than z)
> >   
> As physician I can't find anything unusual here.

I not intending to offend but I think this issue falls more within
Mathematics than Medicine. 

In any case, at least in North America (and I am pretty sure also in
Germany 25 years ago) the z-axis would usually be used for height with x
and y for the base. See for example
http://reference.wolfram.com/mathematica/tutorial/ThreeDimensionalSurfacePlots.html
http://www.omatrix.com/manual/mesh.htm
http://homepages.see.leeds.ac.uk/~lecjm/Teaching/IDL_course/Notes/notes/node27.html



> ----------------------------
> surface – The values of multiple <chart:series> (marked as being of type 
> chart:surface) are interpreted as a 'altitude' at a specific grid 
> location. The graph may visualize these using colors for height 
> intervals, creating color bands.
> In case of chart:three-dimensional="true" a left handed three 
> dimensional Cartesian coordinate system is used with horizontal x axis 
> and vertical y axis (before any 3D scene transformations). The given 
> values for a series are interpreted as y-coordinates (representing the 
> 'altitude'). The accessory x-coordinates are generated from the 
> positions in the altitude-value sequence starting with 1.0. The 
> categories element can be used to define labels for the x axis. The 
> first altitude value in each series gets an x value 1.0. The second 
> altitude value is associated with an x value of 2.0 and so forth. The 
> z-coordinates are generated from the positions of the series elements 
> starting with 1.0. The first series has an associated z coordinate of 
> 1.0. The second series has a z-coordinate 2.0 and so forth. The series 
> names are used as labels at the z axis.
> In case of chart:three-dimensional="false" each altitude value is 
> located on a 2 dimensional Cartesian coordinate system with horizontal x 
> axis and vertical y axis. The categories element can be used to define 
> labels for the x axis. The x-coordinates are generated from the 
> positions in the altitude-value sequence starting with 1.0. The 
> y-coordinates are generated from the positions of the series elements 
> starting with 1.0. The series names are used as labels at the y axis. A 
> third axis element with chart:dimension="z" is used to define the range 
> and separation for the altitude values. In this case the thought 
> coordinate system should be right-handed.
> ----------------------------

I really have a problem with this. If we use the same
chart:class=chart:surface for contour and surface plots then the common
axes should carry the same meaning, so we really shouldn't have y be the
altitude in one and one of the base axes in the other. Moreover the two
non-altitude variables should really be symmetric, ie. virtually
interchangeable. Moreover non-ordinal labels should not used in such a
plot since for the reader of such graphs an ordering is implied.

Not ethat for only 2 visible axes it does not make sense to talk about
right or left handed coordinate systems.
> 
> I hope we can come together somewhere. It really would be good to have 
> this more detailed as it is within the current spec draft!
> Let me know your suggestions!
> 

I would think along the following line:

surface -- this class of charts is used for surface and contour charts.
A single series specifies a rectangular table cell area. Each column of
this area corresponds to a specific x-value while each row corresponds
to a specific y-value. The cell at the intersection of the column and
row gives the altitude (z-value) at the specific location.

The x-values are specified as the first chart:domain. If no chart:domain
is given they default to 1 for the first column, 2 for the second
column, etc.

The y-values are specified as the second chart:domain. If no or only one
chart:domain is given they default to 1 for the first row, 2 for the
second row, etc.

In case of chart:three-dimensional="false" a contour map is shown. Each
altitude value is located on a 2 dimensional Cartesian coordinate system
with horizontal x axis and vertical y axis.  Axis elements with
dimension 'x' and 'y' are used to desribe the visible axes. A third axis
element with chart:dimension="z" is used to define the range and
separation for the colours representing the altitude ranges.

In case of chart:three-dimensional="true" a 3-dimensional surface plot
is shown in a right handed coordinate system with 3 axes of dimensions
'x', 'y' and 'z'. (In this case we would need some specification method
for the view point and view direction.)

Andreas

-- 
Andreas J. Guelzow
Concordia University College of Alberta