Re: [Gnuplot-info] gnuplot xtic question

[Jonathan L. <jl...@fr...>]

I have gone through the code for axis.c in the gnuplot sources. Below=
 is
some pseudo code containing the pieces of code that I think are relev=
ant
to what I am trying to do and also my understanding of what they do.
Again I am using a C program to calculate the position of xtics. Then
when i generate a "set xtics" command that will contain all the tic
values I want along with labels ( which is going to be minutes:second=
s).
The maximum range of what I want to graph will be 1 hour, but
realistically it will be about 500 seconds.=20

I dont understand how the tic interval is calculated in the funtion=
=20
quantize_normal_tics. Could someone explain to me using pseduo code e=
tc
how it works ?

Also the function quantize_duodecimal_tics rounds the tic interval. I=
t
is called from the quantize_time_tics function when the format of the
axis is time. It seems to be similar to the quantize_normal_tics
function.


I would appreciate any responses
Jonathan

---------------------------------------------------------------------=
------

void setup_tics(axis, max)
{

=09//part that im interested in =09
=09//TIC_COMPUTED =3D default; gnuplot figures them
=09} else if (ticdef->type =3D=3D TIC_COMPUTED) {
       =09=09 ticstep[axis] =3D tic =3D make_tics(axis, max);
=09}
}

static double make_tics(axis, guide)
{
=09range =3D absolute(max - min)
=09
=09//i presume tic refers to the tic interval
=09//calculate the tic interval
=09tic =3D quantize_normal_tics(range, guide);

=09//I want to use time data
=09//this rounds the tic interval to a nice figure
=09quantize_time_tics(axis, tic, range, guide);


}

//calculate the tic interval - dont understand the logic behind this
double=09quantize_normal_tics(range, guide)
{
=09floor ( base 10 log of the range)

=09.
=09.
=09.
=09.
=09
=09//seems complicated


}


//round tic interval to a nice value
static double quantize_time_tics(axis, tic, xr, guide)
{
=09//i will be graphing data whose range will be 1 hour maximum
=09//realistically the range will be about 500 seconds
=09//60 * 60 =3D 3600 sec


=09    timelevel[axis] =3D TIMELEVEL_SECONDS;
=09    if (tic > 5) {
=09        /* turn tic into units of minutes */
=09        tic =3D quantize_duodecimal_tics(xr / 60.0, guide12) * 60;
=09        if (tic >=3D 60)
=09            timelevel[axis] =3D TIMELEVEL_MINUTES;
=09    }



}

//again dont understand the logic behind this - it seems to me that i=
t
uses some of the logic from the quantize_normal_tics function
static double=09quantize_duodecimal_tics(arg, guide)
{
=09//seems complicated

}


/* make smalltics for time-axis */
//i presume these are the minor tics.=20
//not exactly sure what order this function is called
static double make_auto_time_minitics(tlevel, incr)
{

=09//part that seems relevant to me

    case TIMELEVEL_SECONDS:
    case TIMELEVEL_MINUTES:
        if (incr >=3D 5)
            tinc =3D 1;
        if (incr >=3D 10)
            tinc =3D 5;
        if (incr >=3D 20)
            tinc =3D 10;
        if (incr >=3D 60)
            tinc =3D 20;
        if (incr >=3D 2 * 60)
            tinc =3D 60;
        if (incr >=3D 6 * 60)
            tinc =3D 2 * 60;
        if (incr >=3D 12 * 60)
            tinc =3D 3 * 60;
        if (incr >=3D 24 * 60)
            tinc =3D 6 * 60;
        break;


}



On Thu, 2005-06-30 at 21:35 +0200, Hans-Bernhard Br=C3=B6ker wrote:
> Jonathan Lynch wrote:
>=20
> > There are potentially ten data points in the space of a second. I=
f i
> > express time in the format 16:19:25.941980 the graph is inaccurat=
e
> > because gnuplot does not support fractions of a second due to usi=
ng the
> > tm structure.
>=20
> It'll only be inaccurate if a second is still wider than one pixel =
on=20
> the actual output format.  Whether that's the case depends on the o=
utput=20
> format, and the length of the interval you have measurements for.
>=20
> > So Im going to stick to plotting the floating point data. Gnuplot
> > generates tics on the x-axis and labels them. What is the algorit=
hm
> > where gnuplot calculates where the tics should be?
>=20
> It's complicated.  The general scheme is: "divide the range into
> intervals of 'nice' length, such that there are between 5 and 10 of=
 them"
>=20
> > I could write a C program to parse through the data file and gene=
rate a
> > file with gnuplot commands. if i knew exactly where the tics were=
 going
> > to be I could put some tics manually eg.
> > set xtics ("16:19:25",58765.0, 16:19:30",58770.0) and so on.
>=20
> Why do you think you have to know the tick placement for that?  Thi=
s=20
> command will override the automatically placed tick positions, so i=
t=20
> doesn't matter where they would have gone.
>=20
>=20
>=20
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