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

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

Ethan A Merritt wrote:
> On Saturday 20 May 2006 01:57 pm, Daniel J Sebald wrote:
> 
>>Ethan A Merritt wrote:
>>
>>>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 plane so that it intersects the z axis
>>>at <foo>.
>>
>>'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.  
> 
> 
> Then let's just get rid of the "no at" form for 'set xyplane'.
> I don't see a need for it.
> 
> With Petr's patch to export GPVAL_Z_MIN and GPVAL_Z_MAX,
> you can accomplish the same thing by saying
> 	set xyplane at func(GPVAL_Z_MIN,GPVAL_Z_MAX)

I don't totally follow what "func" does.  But there may be another problem, one Hans corrected me on something I said in a previous post.  The bottom of the z-axis may not be z_min, if increasing numbers run downward instead of upward.  (That is why I've been making this distinction with "bottom" and "top".)

The idea of a relative placement of the xyplane isn't bad.  It's just that the current ticslevel logic evades me:  if I want the xyplane 20% below the z-axis I type 0.2 and if I want the xyplane 20% above the z-axis I type -1.2.  One can see how that ends up being a trial and error process.  Whereas, I'd think -1.2 for 20% below and 1.2 for 20% above would be easy to comprehend.

Getting rid of the "no at" form of xyplane would be fine too, as a means of not propagating a confusing syntax.  Instead maybe we could use

"set xyplane below 0.2"
"set xyplane above 0.2"

meaning set the xyplane 20% below *z_bottom* or set the xyplane 20% above *z_top*.  To get the xyplane to the center of the z-axis one could type either

"set xyplane below -0.5"
"set xyplane above -0.5"

I don't know if that is very good.  Somehow I like the -1/+1 approach because then to get the xyplane at the center of the z-axis one just types

"set xyplane 0"

It's all one's frame of reference really.

Dan