Voxel layer symbology

A voxel layer contains one or more variables that you symbolize. Depending on the type of data represented by a variable in a voxel layer, you can visualize qualitative discrete or quantitative continuous data. There are two symbology methods you can use to symbolize a voxel layer: unique values or stretch.

Symbology is defined per variable of a voxel layer. For example, you can switch between variables and see the symbology you defined. If the variable of the voxel layer contains qualitative data—for example, the soil types defined in discrete classes—the data is visualized as unique values. If the variable represents quantitative values of continuous measurements, such as temperature, you can visualize this variable using stretch symbology.

An underground model of the Netherlands represents lithoclasses as unique values in this sample set of the GeoTOP model from TNO - Geological Survey of the Netherlands.

Ecological marine units created by USGS and Esri represent water temperature as stretch symbology.

Symbology for a voxel layer is applied to the volume and surface. For example, you can change the symbology, and the changes are applied to the volume as well as to the sections and isosurfaces. You can lock a section of a voxel layer to create a snapshot of the section at the current position, time stamp, and area of interest. The symbology remains the same as the variable of the locked section.

Voxel layers can contain billions of individual voxel cubes. When adding a voxel layer to a scene, the voxel cubes are loaded dynamically until no more voxel cubes are discovered. You can update the symbology to include all values after all voxel cubes are loaded.

Unique values

Unique values symbology assigns a unique symbol to each defined symbol class in a dataset. It allows you to represent qualitative values in a variable. When you add a voxel layer to a scene, the data type is already determined. If the values are discrete, they are represented as unique values. When adding the voxel layer or switching to a discrete variable for the first time, unique values are dynamically loaded. You can show all unique values or select a subset to be drawn in the scene. You can also change the color and the label of the unique values in the Symbology pane.

You can apply transparency to the color of a unique value. Because voxel cubes are building blocks in the voxel volume, the transparency accumulates when voxel cubes overlap. The transparency is not applied to the sections.

You can turn unique values on and off to only show relevant values. Only unique values that have visibility turned on are drawn in the volume and sections, as well as in the Contents pane.

A section with peat, clay, sandy clay, and clayey sand turned on and positions at a borehole is shown in a sample set of the GeoTOP model from TNO - Geological Survey of the Netherlands.

To symbolize a voxel layer using unique values, follow these steps:

1. Select a voxel layer in the Contents pane, and click the Appearance tab.
2. On the Appearance tab, in the Drawing group, click the Symbology button .
The Symbology pane appears. From here, you can modify the applicable symbology for the voxel layer selected in the Contents pane.
3. In the Symbology pane, optionally, choose a Color scheme.

The voxel color scheme is selected by default, but you can choose another color scheme. Check the Show all check box to see all available color schemes in the project.

4. Optionally, click Format color scheme to open the Color Scheme Editor to modify a color scheme.
For more information about color schemes, see Color schemes.
5. Optionally, check the Visible check box next to each unique value to adjust the visibility of the symbol classes.

   When unchecked, the symbol class is removed from the Contents pane and does not draw in the scene.

6. Optionally, click the label associated with a unique value to change it.
7. Optionally, change the heading for the variable to be more descriptive.
8. To change the order of the symbol classes, click Move selected value(s) up or Move selected value(s) down.

   The symbol class order is reflected in the Contents pane and in the legend on a layout.

9. To remove unique values, right-click and click Remove. The removed unique value is automatically added to <all other values>. To hide <all other values>, turn off the visibility.
The maximum number of symbol classes is 255. Unique values are dynamically loaded until no new unique values are discovered. To add additional symbol classes, click Add unlisted values to open a table in the Select values to add pane. This table lists all values not currently symbolized. Click Options and click Add new value to type a new value.
You can make this change in the Symbology pane or in the Contents pane.

Stretch

Stretch symbology allows you to define how the values are stretched between a minimum and maximum value that is associated with a color scheme, which represents quantitative data such as temperature or oxygen.

Use symbology to explore your voxel data further. Filter the data to show only values you are interested in using the Min and Max range options. These values can be changed by adjusting the Data Filter in the Symbology pane.

By default, the histogram shows the significant data range. The values are exaggerated by a factor of 2 to increase readability of the histogram. To view the value without the exaggeration, click the Show Significant Data Range check box from More option.

A histogram of temperature with a data filter set from 0 to 25 degrees Celsius is shown with values exagerated by a factor of 2.

A transparency function in stretch symbology can emphasize specific values by making other values transparent. For example, to highlight a high concentration of pollution, you can make lower pollution values transparent. Use an isosurface to show pollution concentration at a specific value.

For example, you can apply the transparency function to a temperature variable in an ecological marine unit voxel layer:

An ecological marine unit voxel layer is shown with concentrations of pollution at different transparency levels.

The transparency function is applied to a voxel layer.

To symbolize using stretch symbology, follow these steps:

1. Select a voxel layer in the Contents pane and click the Appearance tab.
2. On the Appearance tab, in the Drawing group, click the Symbology button .

   The Symbology pane appears.

3. In the Symbology pane, optionally choose a new Color scheme.

Check the Show all check box to see all available color schemes. Click Format color scheme to open the Color Scheme Editor to modify a color scheme.

4. Optionally, check Data Filter to set a filter and set the Min and Max values.
When a voxel layer is loaded, not all data may be available right away. You can change the Data Filter settings in the Symbology pane to define a data range. All values that are not drawn are gray.
5. Optionally, change the Color range and set the Min and Max values.
6. Optionally, check Transparency function.
   1. Interactively change the position of the control points. To add a new control point, double-click the transparency function graph or change the transparency settings.
   2. Modify the Value and Position settings interactively for each control point by moving the point on the transparency function graph. Alternatively, add a value to the Value and Position dialog boxes.

      The first and last control point cannot be deleted.

Advanced options for stretch symbology

Advanced symbology options allow you to customize the formatting of numeric labels in a voxel layer's legend to better represent the symbology. You can specify whether the numeric field data values represent percentages, directions, currency, rates, fractions, or angles. You can also format labels using scientific notation (standard format) or create a custom format string for the label. You can access advanced symbology options by clicking Advanced symbology in the Symbology pane.

In addition to formatting legend labels in the scene, you can also format the layout legend. For information about formatting legend text symbol styles and fonts in layouts, see Format a legend item.