Hi Beni,

yes origin can be negative. And spacing can also be negative. It is just
checked not to be equal to 0.

I am just not sure - whether the orientation of 3D model triangles will not
be messed if the negative spacing is used.

S.

On Wed, 24 Feb 2021 at 11:12, Benedikt Hallinger <beni@hallinger.org> wrote:

> So, after reading the thbook (p. 31) again, I think I can answer that to
> myself.
> But it would be good if someone could step in and confirm:
>
> > <origin x> <origin y>
> may be negative, depending in used CS.
>
> > <x spacing> <y spacing> <x count> <y count>
> Is not allowed to be negative:
> - origin is always lower-left (southwest) corner, and spacing is assumed
> to be from west to east and south to north, thus always positive.
> row and cols count cannot be zero or negative for obvious reasons.
>
>
> Stay safe!
> kind regards, Beni
>
>
> Am 2021-02-24 8:18, schrieb Benedikt Hallinger:
> > Good morning,
> > while debugging
> > https://github.com/hbeni/therionsurface2survex/issues/1 i stumbled
> > upon a format question i did not give tought until yesterday.
> >
> > With the "grid" command you specify coordinate origin and size of a
> > surface grid:
> >   grid <origin x> <origin y> <x spacing> <y spacing> <x count> <y
> > count>
> >
> >
> > Until now i assumed that:
> >
> > a) these data has to be all positive.
> > But i'm not sure... origin may surely get negative (like in wgs89 and
> > for example western and southern of the 0-meridian/equator)
> > And also stepsize - might it get negative too (esp. with flipped grids
> > maybe)?
> >
> > b) the spacing might only be integer numbers, not floats
> > Is this true? I just got an example with not-round stepsize.
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