Regardless of whether your cell-based data is an image from a satellite or aerial sensor or a raster dataset representing gravitational modeling or a DEM, there are many ways that you can work this data when doing an analysis. For example, you may want to visually analyze the data, use it as a background (basemap) to visually analyze other data, or use it in an analysis operation.
If you're using the image or raster data in a visual analysis, you may be examining the results of a watershed study, looking for features in a shaded relief created from a digital elevation model (DEM), or changing band combinations to identify features. If you're using the data to help analyze other data, you may be examining and updating vector data, such as roads, by using up-to-date imagery as a basemap to determine the location of any missing roads. For any of these types of analyses, you are most likely concerned with the visual appearance of the data. You should consider the types of renderers used to display the imagery and raster data (such as the Stretched or RGB Composite renderers) and may want to alter these, apply different types of stretches to the histogram to enhance specific information in the dataset, or even remove some of the values of the raster from the display.
For information on displaying imagery and rasters using the different types of renderers, see Renderers used to display raster data. For information on other aspects of the dataset's appearance and behavior, such as faster rendering, performance tuning, enhancing the contrast, or changing the appearance of background values, see Improving the display of raster data. There are also tools to balance the appearance of multiple images to make them look like a single seamless image. For more information, see Color correction of raster data or Color correcting a mosaic dataset.
If the data you are displaying is satellite imagery, then it's likely supported as a raster product within ArcGIS. If this is so, then you should add it to your display using the desired template from the raster product. There are settings within the application that help ensure that these are displayed correctly.
Interactively improving the rendered image
There are many tools on the Image Analysis window to help you improve the appearance of the image by altering how the histogram is stretched. The sliders adjust the contrast , brightness , and gamma of the image. The Interactive Histogram Stretch button is useful to help you understand the distribution of pixel values and adjust how they are stretched.
Interrogating the images and pixel values
There are additional tools in ArcMap to help you in your analysis of raster data, such as the Pixel Inspector tool , which is used to view an area of pixel values in your raster dataset, or the Swipe Layer tool , which is used to interactively reveal layers beneath the layer being swiped. To learn about these tools and others, see the following:
- Using the Pixel Inspector
- Interactively reveal rasters using the Swipe Layer tool
- Revealing rasters using the Flicker tool
You can also use the Identify tool to get pixel value information for a single pixel, or use the Get Cell Value tool when you're working in a geoprocessing model.
Analysis and processing functions
The Image Analysis window provides access to both processing and display capabilities for raster data. You can easily display a DEM as a shaded relief and modify the color ramp. There is also a tool to perform a difference so you can see if there have been any changes between two datasets, and you can easily merge multiple rasters into one .
One special capability the Image Analysis window provides is adding functions to the raster layers. You can modify these functions and perform more advanced analysis on your raster data. Many of the buttons in the Processing section of the window insert functions into the layer. There is also an Add Function button to give you access to the function chain so you can pick the processing function you want applied and chain them together to create more complex analyses. These functions are applied as you access the data and are saved within the layer files.
Making measurements from the imagery
The Image Analysis window also contains a set of mensuration tools including tools to measure point, distance, angle, height, perimeter, and area from an image (raster dataset or mosaic dataset) with sensor information (or geodata transformation).
Mensuration is defined as applying geometric rules to find the length of lines, areas of surface, or volumes using the information obtained from lines and angles. It can also include measuring the height and absolution location of a feature.
Extensions for analysis
There are many ways to use raster data in analysis operations. When performing these operations, your main concern will probably be with the data represented by the values of the cells; therefore, you will be performing operations that manipulate these values. There are many tools in ArcGIS for Desktop that allow you to work with raster data for data management, conversion, and transforming; however, to utilize raster data within an analysis operation, you will need one of the extensions.
There are ArcGIS extensions that enhance the analysis capabilities of raster data. These are
- ArcGIS Spatial Analyst extension—This extension provides a comprehensive set of advanced spatial modeling and analysis tools that allow you to perform integrated raster and vector analysis.
- ArcGIS 3D Analyst extension—This extension allows you to effectively visualize, analyze, and generate surface data and provides the tools for three-dimensional modeling and analysis.
- ArcGIS Geostatistical Analyst extension—This extension provides the capability for surface modeling using deterministic and geostatistical methods.
When using the geoprocessing tools provided by ArcGIS or either of these extensions, you can automate your workflows by building models to perform your analysis. Building models allows you to chain the tools together.