Re: [Gnuplot-info] Draw rectangle on 3D surface

[Ethan M. <eam...@gm...>]

On Fri, Sep 26, 2014 at 12:11 AM, GOO Creations <goo...@gm...> wrote:
> Hi,
>
> I'm trying to draw a simple rectangle on a surface graph. This is what I
> have:
>
>     set obj 1 rect at graph 0.5, 0.955 size 10, 5 fs transparent solid 0.7 fc rgb "black" front
>     splot inputfile u 1:2:3/
>
>
> The label draw correctly, however the rectangle doesn't show. If I
> cahnge the surface to a heat map (set pm3d map), the rectangle shows.
> Also when drawing the rectangle on the surface with screen from and to
> coordinates, it also shows.
>
> So my question: why doesn't the rectangle show when using either "at
> graph <position> size <size>"or "at screen<position> size <size>"? What
> am I doing wrong?

Rectangles in graph or axis coordinates can be not drawn in 3D,
because once you rotate the 3D view the object is no longer a
rectangle per se.   It can, however, be described as a general polygon
that just happens to come out rectangular when viewed in a 2D
projection.

Here is an example:

set obj 2 polygon from -10,-10,1 to -10, -5, 1 to -5, -5, 1 to -5, -10, 1
set obj 2 fs solid 1 fc rgb "cyan" front
set hidden3d
splot tanh(x**2+y**2)

This probably should be mentioned somewhere in the documentation.
Rectangles described in screen coordinates always work.