# INTENSITY GRAPHS AND CHARTS IN LABVIEW

## INTRODUCTION

Use the intensity graph and chart to display 3D data on a 2D plot by placing blocks of color on a Cartesian plane. For example, you can use an intensity graph or chart to display patterned data, such as temperature patterns and terrain, where the magnitude represents altitude. The intensity graph and chart accept a 3D array of numbers. Each number in the array represents a specific color. The indexes of the elements in the 2D array set the plot locations for the colors. The below Figure shows the concept of the intensity chart operation.

The rows of the data pass into the display as new columns on the graph or chart. If you want rows to appear as rows on the display, wire a 2D array data type to the graph or chart, right-click the graph or chart, and select Transpose Array from the shortcut menu. The array indexes correspond to the lower-left vertex of the block of color. The block of color has a unit area which is the area between the two points, as defined by the array indexes. The intensity graph or chart can display up to 256 discrete colors.

## INTENSITY CHARTS

After you plot a block of data on an intensity chart, the origin of the Cartesian plane shifts to the right of the last data block. When the chart processes new data, the new data values appear to the right of the old data values. When a chart display is full, the oldest data values scroll off the left side of the chart. This behavior is similar to the behavior of a strip chart. The below Figure shows an example of an intensity chart.

The intensity chart shares many of the optional parts of the waveform chart, including the scale legend and graph palette, which you can show or hide by right-clicking the chart and selecting Visible Items from the shortcut menu. In addition, because the intensity chart includes color as a third dimension, a scale similar to a color ramp control defines the range and mappings of values to colors. Like the waveform chart, the intensity chart maintains a history of data, or buffer, from previous updates. Right-click the chart and select Chart History Length from the shortcut menu to configure the buffer. The default size for an intensity chart is 128 data points. The intensity chart display can be memory intensive.

## INTENSITY GRAPHS

The intensity graph works the same as the intensity chart, except it does not retain previous data values and does not include update modes. Each time new data values pass to an intensity graph, the new data values replace old data values. Like other graphs, the intensity graph can have cursors. Each cursor displays the x, y and z values for a specified point on the graph.

## USING COLOR MAPPING WITH INTENSITY GRAPHS AND CHARTS

An intensity graph or chart uses color to display 3D data on a 2D plot. When you set the color mapping for an intensity graph or chart, you configure the color scale of the graph or chart. The color scale consists of at least two arbitrary markers, each with a numeric value and a corresponding display color. The colors displayed on an intensity graph or chart correspond to the numeric values associated with the specified colors. Color mapping is useful for visually indicating data ranges, such as when plot data exceeds a threshold value. You can set the color mapping interactively for the intensity graph and chart the same way you define the colors for a color ramp numeric control.

You can set the color mapping for the intensity graph and chart programmatically by using the property node in two ways. Typically, you specify the value-to-color mappings in the property node. For this method, specify the Z scale: Marker Values property. This property consists of an array of clusters in which each cluster contains a numeric limit value and the corresponding color to display for that value. When you specify the color mapping in this manner, you can specify an upper out-of-range color using the Z scale: High Color property and a lower out-of-range color using the Z scale: Low Color property. The intensity graph and chart are limited to a total of 254 colors, with the lower and upper out-of-range colors bringing the total to 256 colors. If you specify more than 254 colors, the intensity graph or chart creates the 254-color table by interpolating among the specified colors.

If you display a bitmap on the intensity graph, you specify a color table using the Color Table property. With this method, you can specify an array of up to 256 colors. Data passed to the chart are mapped to indexes in this color table based on the color scale of the intensity chart. If the color scale ranges from 0 to 100, a value of 0 in the data is mapped to index 1, and a value of 100 is mapped to index 254 with interior values interpolated between 1 and 254. Anything below 0 is mapped to the out-of-range below color (index 0), and anything above 100 is mapped to the out-of-range above color (index 255).