User Function: PHPLOT can accept data in a number of different
formats. One main difference between PHPLOT and PGPLOT
is that the x-y or x-y-error data should be passed in
with the data grouped together in an array.
Asside: Why the author chose this data format: In PGPLOT
you would have the X-values in one array and the Y-values
in a second. This would sometimes lead to really strange
graphs if one array was accidentally one data element
short. Plus most of the data the author was using came in
from a database using a _get_row or _get_array (in php)
and one can just pass it straight in to PHPLOT.
Colors and border colors are set by SetDataColors. Why
not have colors as part of the same array? Because most
data applications are used to putting out raw data and not
raw data + color information.
So in PHPLOT the datalabel,x-value,y-value and error are
grouped together as a value array. Then the
entire set of points to be plotted is passed in as a data array
E.g. Data_array = array(value_array_1,value_array_2,....)
See below for examples of the various data types:
text-data: Data is displayed at equal spacing along the x-axis. Data
is passed in as a data array of value arrays. Each element of the data
array is a position on the x-axis. The first element of the value array is
the label for that x-axis position, every subsequent element of the value
array is a y-value.
Example data
$data = array(
array("label 1",1.1,2,3,4),
array("label 2",2,3,4,5),
array("label 3",5,6,7,8),
array("label 4",10,12,13,14)
);
Which will display data points at
(1,1.1), (1,2), (1,3), (1,4), (2,2), (2,3)....
data-data:
X-Y data is passed in like text-data except
that the second element of the value array is the position along the
x axis of the data point(s). One data element would be $data[] = (title,x,y1,y2,y3,y4,...)
or
$data = array(
array("label 1",1.1,2,3,4),
array("label 2",2,3,4,5),
array("label 3",5,6,7,8),
array("label 4",10,12,13,14)
);
Notice that this is the same as in the previous example except that
the x,y data points are at (1.1,2), (1.1,3), (1.1,4), (2,3)...
data-data-error:
Again X-Y data is passed in as an array with each value
array being (data_label,x_position,y_position,error_plus,error_minus)
User Function: Used for x_grid_label_type="time".
For the format see the php manual for strftime(). It assumes the x-data values are unix timestamps, and displays them according to the passed format string.
Example: If x values are seconds offset from the beginning of the day. This coresponds to unix timestamps on January 1, 1970, so all I had to do was $graph->SetXGridLabelType("%H:%M") to display the time properly.
The php strtotime() function also comes in handy turning dates into timestamps, especially for parameters to SetPlotAreaWorld().
Example:
$graph->SetPlotAreaWorld(strtotime("October 1"), 0,strtotime("December 15"),10);
$graph->SetXGridLabelType("time") ;
$graph->SetXTimeFormat("%b %d") ;