Multispectral imagery is a powerful tool for distinguishing types of materials and features in the landscape. Natural and man-made materials often have unique spectral signatures that can be used to identify them quantitatively. Spectral profiles allow you to select areas of interest or ground features on the image and review the spectral information of all bands in a chart format. A spectral profile consists of geometry to define the pixel selection and an image with key metadata from which to sample.
Create a spectral profile
To create a spectral profile, on the Analysis tab, select the Profiles drop-down button and click Spectral Profile to open the Chart Properties pane.
Define an area of interest for your spectral profile
There are several options for defining the set of pixels you want to profile. You can use the Define an area of interest tools at the top of the Chart Properties pane to delineate an area or feature of interest in the map view.
The pixel values of the image bands that intersect the area of interest will be plotted. The area of interest sketch tools include a point, line, circle, rectangle, polygon, and freeform shape. Additionally, you can define an area of interest by selecting a line, point, or polygon feature layer in the map view that overlays the image. Use the color picker to choose a color when defining your area of interest. Use different colors for the various features you want to compare with your spectral profile.
Define your spectral profile
Each area of interest you collect is listed in a table under Spectral Profiles and is given a default label such as Profile_1, Profile_2, and so on, as they're collected. To assign your own labels, select the label for an area of interest, type a new string, and press the Tab key to register the string. Labels are stored as you type them, making them available in the pick list for reuse.
Check the Enabled check box to manage the area of interest, which enables the area of interest to be displayed in the spectral profile chart and map view. You can also delete the area of interest or move it to a different position in the list using the up and down arrows. These selections determine what data is processed and displayed in your spectral profile chart and how the data is visualized.
When the spectral profile is defined using a collection of pixels, the default visualization is a line chart. You can also choose to display the spectral profile as another plot type.
The best plot type for a spectral profile defined with a point is the Mean Line option because a range of values is not available.
You can create a spectral profile of a single band image, but the Mean Line option for Plot Type will be unavailable. The spectral plot of a single band image displays useful information such as the minimum, maximum, median, and quartile values.
Several plot types are available to visualize and analyze your spectral profile data. Data for each enabled area of interest, or the entire image, is processed and displayed in the spectral profile chart of choice.
A mean line plot is a line connecting the mean values within a set of pixels, per band. Point collections have no mean value and use the point pixel value collected in each image band.
The Boxes chart type allows you to visualize and compare the distribution and central tendency of the set of pixels collected through their quartiles. Quartiles are a way of categorizing numeric values into four equal groups based on five key values: minimum, first quartile, median, third quartile, and maximum.
The box portion of the chart illustrates the middle 50 percent of the data values, also known as the interquartile range (IQR). The IQR illustrates the variability in a set of values. A large IQR indicates a large spread in values, while a smaller IQR indicates most values fall near the center. For example, an agriculture field with varying degrees of emerging crop will have high variability, while bare fields or those with mature crops will have lower variability within their spectral identity. Box plots also illustrate the minimum and maximum data values through statistical whiskers (vertical lines) extending from the box, and optionally, outliers as points extending beyond the whiskers.
Boxes and mean lines
This type of chart plots boxes and a line graph connecting the mean values within the set of pixels comprising your area of interest. It shows multiple boxes and multiple lines for each ground feature in each spectral band.
Consolidated boxes and mean lines
This type of chart consolidates the range of the boxes into a single box with a new range, IQR, median, and quartiles, while also displaying the mean lines from each profile.
This chart is useful when collecting similar features, segments, or interactively collecting similar features. For example, it's a good choice for comparing agricultural fields growing the same crop when each may have varying levels of health, leading to varying yields.
Outliers are useful to gain further insight into your data. Outliers are available for Boxes, Boxes and Mean Lines, and Consolidated Boxes and Mean Lines chart types. You can select the outliers in the chart, and those pixels will be highlighted on the screen. For example, you can create an information product from multispectral imagery such as NDVI. Draw or select an area of interest, display the outliers on the spectral plot, select them, and view exactly which portions of the fields are stressed and may need attention.
Spectral profile charts are composed of an x-axis and a y-axis. The x-axis is determined by the number of bands in the image being profiled and the wavelengths associated with each band. Pixel values for the image bands are displayed along the y-axis. The appearance of your chart's axis are set in the Chart Properties pane Axis tab.
The x-axis displays the bands and wavelengths of the electromagnetic spectrum for each band. When plotting Boxes, Boxes and Mean Lines, and Consolidated Mean Lines, the x-axis is determined by the number of bands in the image, not the wavelength. Each tick on the x-axis shows the band name where that data was derived. Hover over the boxes in the plot to see wavelength information. For Mean Line charts, the x-axis displays only the wavelength.
When using a single band image from a derived dataset such as NDVI, the x-axis is unitless. Each bar on the x-axis correlates to each ground feature profile collected.
The y-axis is used to measure pixel or ground feature values composed of statistical measurements for minimum, first quartile, median, third quartile, and maximum values. Default minimum and maximum y-axis bounds are based on the range of data values represented on the axis. These values can be customized by typing a desired axis bound value. Clicking the reset button returns the axis bound to the default value. This is helpful when the boxes do not have a wide range of values and appear very small.
You can format how the y-axis displays numeric values by specifying a number format category or defining a custom format string.
The legend displays one line or square for each spectral profile, using the same color and name as the profile in the Spectral Profile table. The first click on the legend item will cause the line or box to disappear from the profile graph, but a second click on the same legend item will cause the line or box to reappear.
Change spectral profile appearance
Your visualizations should be attractive as well as informative. Whether you want a dark chart background because you prefer to work in a dark theme, or you want to customize the look of your charts before you share them, you can format your chart's appearance through the Format tab in the Chart Properties pane.
You can choose one of the predefined system themes or use custom formatting for the text and symbol elements in your chart. When you're satisfied with your chart's appearance, you can save the format as a custom theme that can be applied to other charts.
The color of each area of interest will be the same by default. To change the color, click the color to be changed on the Data tab of the Charts properties pane
Format text elements
A chart's text elements can include the following:
- Chart title
- Axis titles
- Axis labels
- Legend title
- Legend text
- Guide labels
- Data labels
- Description text
To format your chart's text elements, complete the following steps:
- In the Chart Properties pane, on the Format tab, click the Text elements tab .
- Choose and format text elements individually or click All Text to format all text elements at once.
Format symbol elements
A chart's symbol elements can include the following:
- Background color
- Axis lines
- Grid lines
To format your chart's symbol elements, complete the following steps:
- In the Chart Properties pane, on the Format tab, click the Symbol Elements tab .
- Choose Background from the symbol element list and change the color by picking a new color from the color picker drop-down menu.
- Choose and format line elements individually or click All lines to format all lines at once.
Save a custom theme
To save chart format settings as a customer theme, complete the following steps:
- Configure an existing chart's text and symbol elements as you would like them to be saved.
- In the Chart Properties pane, on the Format tab, click the Chart themes tab , and then click Save as custom theme.
The format settings are saved as a new custom theme in the theme gallery.
- Give your custom theme a descriptive name by right-clicking the theme and choosing Rename. Chart themes can be permanently deleted from the theme gallery by right-clicking the theme and choosing Delete.
Custom themes are saved to %AppData%\Roaming\Esri\Drone2Map\CustomGallery. Deleting a theme from the custom gallery permanently deletes the file.
Apply a chart theme
To apply an Esri-provided system theme or a custom theme to your chart, complete the following steps:
Properties pane, on
the Format tab, click
themes tab , and then choose
a theme icon from the theme gallery.
The theme is applied to the active chart.
- Optionally, make additional changes to any of the text or symbol elements and save them as a new custom theme.