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## 6.9 Specifying the scale manually

Normally the automatic scaling should be doing an adequate job in most circumstances but there might be cases where you like to manually set the scale. For example if you have several graphs where you like to be able to easily compare them and therefore want them all to have the same scale.

To specify a manual scale you have to add arguments to the standard Graph::SetScale() method. So to specify that you want an Y-scale between 0 and 100 you need to write

`$graph->SetScale("textlin",0,100);`

When you specify a scale manually there is one additional thing you need to decide. How the tick marks should be positioned. You have three choices

1. Let JpGraph decide suitable tick marks honoring the exact scale you specified. This is the default behavior if you don't do anything else.
2. Allow JpGraph to slightly adjust your specified min and max values. With the default method, depending on the min and max values, the end and start of the scale might not fall on an exact tick mark. For esthetic reasons you might still want the last/first tick mark to fall on the edges of the scale. By calling LinearScale::SetAutoTicks() you tell JpGraph to make the smallest necessary adjustment of the end/start points so that they fall on an exact tick mark.
3. Manually specify the tick marks with a call to LinearTicks::Set() For example
   `$graph->SetScale("textlin",0,100);
   $graph->yscale->ticks->Set(10,5);`

   Will set the major tick marks every at 0,10,20,.. And every minor tick mark in between (0,5,10,15,20,25,...).

The three images below illustrates the difference between the three possibilities of ticks for a manual scale.

Figure 1: Manual scale, manual ticks major=7 minor=2 [src] | Figure 2: Manual scale, automatic ticks with exact limits [src] | Figure 3: Manual scale, automatic ticks where we allow adjustments of the limits [src]

## 6.10 Adjusting the automatic tick marks

You can adjust the automatic tick marks by telling JpGraph how dense you want them to be. You use the Graph::SetTickDensity() method. You can set the density setting in four steps

- TICKD_VERYSPARSE, Very few ticks
- TICKD_SPARSE, Few ticks
- TICKD_NORMAL, Standard number of ticks
- TICKD_DENSE, Large number of ticks

Taking the previous example with the manual scale but automatic ticks and using a denser ticks setting gives the following result

Figure 4: Manual scale with automatic ticks but with a denser tick settings. [src]

## 6.11 Handling date/time scales

A common plot type is to have a date/time scale on the X-axis. Even though there is not special support for a time scale this is easy to accomplish.

In the following we will assume that all data points are specified by a tuple where the date/time is specified as a timestamp in second in the same format as is returned by the PHP function time().

The trick here is to use a label formatting callback routine which gets called to format each label on the scale.

What we do is that we specify that the X-scale should be an ordinary "int" scale (remember that the data values are timestamps which are integers). We then install our custom label callback (with a call to SetLabelFormatCallback()) which given a timestamp formats it to a suitable human readable form. In our example we will use the PHP function Date() for this purpose.

The callback we use will be

`// The callback that converts timestamp to minutes and seconds
function TimeCallback($aVal) {
return Date('H:i:s',$aVal);
}`

Using some random data we can now generate the following graph

Figure 5: Example on how to format an axis to hold a date/time scale using and integer scale and a callback routine [src]

In the above example we have specified the X-scale manually to make sure that the min/max values on the X-axis exactly matches the min/max x-data values.

## 6.12 Adjusting labels on a text scale

In the following section we will work through an number of examples on how to manipulate labels on a text scale. Primarily we will investigate how to best handle the case where you have a large number of values.

As a remainder; Text scale is meant to be used on the X-axis when the X-axis doesn't have a numeric value, i.e you are only interested in linear ordering of the data. If you don't specify the labels manually they will be set automatically starting from 1 as the example below shows.

Figure 6: A simple bar plot using an automatic text scale [src]

To specify the labels on the X-axis as suitable text strings you call the method Axis::SetTickLabels() with an array containing the text-labels. If there are more data points than labels the non-specified labels will be given their ordinal number. If we augment the previous example with the name of the month we get the following new example

Figure 7: Manually specifying the text scale labels [src]

Tip: To get hold of localized version of the month names (or weekdays) you can use the DateLocal class available in the global variable $gDateLocale If no locale has been specified the default locale for the installation will be used.

What happen now if we have a larger number of bars? Let's try with 25 bars and see what result we get.

Figure 8: A larger data set [src]

Not all to impressive. The labels are to close and they overlap. Hence it is not a good idea to display every label. To adjust what labels are to be displayed you use the SetTextLabelInterval() method. The argument to this method is the interval between text labels. So to display only every 3 month you would add the line

`$graph->xaxis->SetTextLabelIntervall(3)`

Which would give the result shown below

Figure 9: Displaying only every third label [src]

Much better, quite readable.

If we have an even larger data set it might not longer be meaningful to display all the tick marks since they would simple become to close. In JpGraph there is a possibility to specify that you only would like every n:th tick mark to be visible ( SetTextTickIntervall() ). For bar graphs using text scale however, that might not be such a good idea since the tick marks are between the bars and the labels centered under the bars. If we only were to display, say, every 3 tick mark it wouldn't look to good. Not that we can't do it, as the example below shows, but it just doesn't look very good.

Figure 10: Displaying just every third tick mark. [src]

A better way to handle large data set is simply to hide the tick marks all together. Tick marks may be hidden by calling the method Axis::HideTicks(); If we hide all the ticks on the X-axis we will get the result shown below

Figure 11: Hiding all tick mark. [src]

More ... [ TBC ]

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