Re: z_floor and z_ceiling (was Re: various observations)

[Daniel J S. <dan...@ie...>]

Ethan A Merritt wrote:
> On Saturday 20 May 2006 12:01 am, Daniel J Sebald wrote:
> 
>>>OK people, any preference as to xyplane (not 'ticslevel') having bottom 
>>>of zrange as 0 and top of zrange as 1? 
>>
>>That is should top of zrange be 1 or -1 for 'xplane'?
> 
> 
> I was not following this thread, and now that I look back through
> it I don't understand what the issue really is.
> 
> I never did understand 'set ticslevel', but whatever it did should
> stay that way for backwards compatibility.
> 
> The idea behind 'set xyplane <foo>' is [supposed to be] obvious:
> Whatever zrange is, whatever way round the axes are pointing,
> yadda yadda,   draw the place so that it intersects the z axis
> at <foo>.  Have you found some case where this doesn't happen?

But unless you've mis-typed, you have that wrong... and this is an example of the source of confusion.  'set xyplane *at* <foo>' does as you explain, and that works just as advertised.

The problem is the "percentage of z-axis" form, i.e., the non "at" form, the form for which the actual values on the z-axis do not matter; rather the user wants the xyplane to be somewhere relative to the z-axis visually.

Somehow we are trying to make a linear number range represent that concept.  Some logical choices would be

bottom     top
z-axis    z-axis
value     value
------    ------
  0         -1     (current)
  0         +1     (I think more intuitive)
 -1          0     (just as intuitive I guess)
 +1          0     (no)
 -1         +1     (maybe *this* is the most intuitive choice)
 +1         -1     (no way!)

My point in all this is that I have no qualms about someone wanting axis values to be increasing in one direction or the other (I've seen things plotted many ways and for various reasons), but when we step one level back and speak of the axis relatively, the convention is increasing to the right, increasing up I would think.

As it stands, 0/-1 is the way non-at 'xyplane' is going to be for consistency with 'ticslevel'.   "ticslevel at <foo>" will not be allowed.

Dan