Tutorials: Sentinel-2 Time Series Analysis Tutorial, Landsat Time Series Tutorial, Temporal Processing Examples

You can build a series of images (called a raster series) for spatiotemporal analysis, then view the images incrementally. Use the steps below to build a raster series file (.series), which is a text file in JSON format that references the locations of images within the series. You need to build a raster series file before you can view the series, which is described in the following sections.

You can also write scripts to build a series using the BuildRasterSeries task or BuildTimeSeries task. See the BuildRasterSeries task topic for an example of building a raster series from HDF5 data or NITF files that have multiple image segments.

Build a Raster Series

  1. Choose one of the following options:
    • From the Toolbox, select Spatiotemporal Analysis > Build Raster Series.
    • From the menu bar, select File > New > Build Raster Series.
  2. Click the Browse button next to the Input Rasters field. The Data Selection dialog appears.
  3. In the Open dialog, navigate to the files and select the images to include in the series, then click Open.
  4. In the Data Selection dialog, click Select All to select the rasters, then click OK. The rasters are added to the Input Rasters field in the Build Raster Series dialog. You can change the order the list by dragging and dropping the names, or by clicking the Sort Alphabetically button .
  5. To order the rasters in the series chronologically, from oldest to newest, select Yes. If you are not performing a time-series analysis and only want to create a group of images where chronological order is not important, select No.
  6. Enter a filename and location for the JSON-formatted series (.series). Save the file in the same folder as the images.

  7. Enable the Display result check box to display the output in the view when processing is complete. Otherwise, if the check box is disabled, the result can be loaded from the Data Manager.

  8. To reuse these task settings in future ENVI sessions, save them to a file. Click the down arrow next to the OK button , select Save Parameter Values, then specify the path and filename to save to. Note that some parameter types, such as rasters, vectors, and ROIs, will not be saved with the file. To apply the saved task settings, click the down arrow and select Restore Parameter Values, then select the file where you previously saved your settings.

  9. You can run the process in the background on your computer or in the background on an ENVI Server (if available). Click the down arrow next to the OK button and select one of the following:

    • Run Task in the Background: Runs the process on your computer. This method does not use an ENVI Server. The job progress will show in the ENVI Job Console's Background Jobs tab.
    • Run Task on envi_server_name. Runs the process on the selected ENVI Server. The job progress will show in the ENVI Job Console's envi_server_name tab.

    See ENVI Job Console for details on monitoring ENVI Server jobs and viewing results. See ENVI Servers for details on configuring and using an ENVI Server.

  10. Click OK to create the series file.

Build a Series from Files That Contain Multiple Datasets

This section applies to Multi-page TIFF, NITF with multiple image segments, Proba-V, and SkySat-1.

  1. Use the File > Open menu option to open one or more data files.
  2. From the Toolbox, select Spatiotemporal Analysis > Build Raster Series.
  3. Click the Add Raster button, then select Add Open Raster.
  4. In the Data Selection dialog, use the Ctrl key to select individual datasets or image segments (NITF) from each file.
  5. Click OK, then continue with Step 3 in Build a Series.

Regrid a Raster Series

The images that comprise a spatiotemporal series do not necessarily have to be in the same map projection or have the same spatial extent. An example is animating a time series to track a hurricane; in this case, it is not critical that the images have the exact spatial extent, projection, or resolution. However, ensuring a common projection and spatial extent allows you to perform a true spatiotemporal analysis, for example, studying the change in atmospheric pressure or a glacier's extent over time in a specific location.

Follow these steps to build a gridded raster series. You do not need to perform these steps with MODIS, NPP VIIRS, or GRIB data because they are already gridded to the same spatial reference.

You can also write a script to build a gridded raster series using the following tasks: RegridRasterSeries, RegridRasterSeriesByIndex, RegridRasterSeriesByUnion, and RegridRasterSeriesByIntersection.

Expand the Spatiotemporal Analysis folder in the Toolbox and select a Regrid option. The following sections describe each option.

Regrid Raster Series

This tool lets you define a custom grid to which all rasters in a series will be regridded. A custom grid definition provides the information needed to georeference rasters and vectors to a common coordinate system. It does not refer to any raster or rely on any specific raster to set its extents.

A custom grid definition provides the following information:

  • Coordinate system
  • Spatial (geographic) extent
  • Pixel (cell) size
  • Rows and columns
  • Tie point pixel and map coordinates

Creating a custom grid definition requires you to know some details about the coordinate system of the current raster series and the coordinate system that it will regrid to. For example, suppose that you have a raster series that is in a UTM (WGS-84) coordinate system. You want to regrid the series to a State Plane coordinate system in units of U.S. Survey Feet. One option is to define the spatial grid based on a combination of coordinate system, spatial extent, and pixel size. With this option, you must know the latitude and longitude coordinates of the four corners of the desired spatial extent. Then convert these to State Plane coordinates, according to your specific State Plane zone. (Many conversion tools are available online.) Also convert the pixel size from meters to feet.

Follow these steps to regrid a raster series to a custom grid definition:

  1. In the Input Raster Series URI field, select a .series file for input.
  2. From the Grid Definition drop-down list, select the desired combination of grid parameters to define:
    • Coord. system + extents + pixel size
    • Coord. system + extents + img. size
    • Coord. system + pixel size + img. size + tie point
  3. Enter the values for each grid parameter as follows. The available fields will vary, depending on the Grid Definition you select:

    • Coordinate System: Specify the coordinate system using one of the following:

      • Click the Browse button to open the Select Coordinate System dialog. See Select Coordinate Systems for further instructions.
      • Click the Import from dataset button to import the coordinate system of an existing dataset.
      • Click the Import from current view button to have ENVI import as many grid parameters as possible from an existing view, including the coordinate system, spatial extent, pixel size, and tie point location and coordinates.

      • Click the Calculate Union/Intersection button to open the Calculate from a Group of Rasters dialog. In the dialog, select Intersection to include only the extent where the rasters overlap, or select Union to include the extent encompassed by all of the rasters.

      • With an input raster in the view, click the Draw Bounding Box button , then click and drag the cursor to define a box outlining the extent of the layer stack.
    • Extents: Enter the spatial extent coordinates in the same units as the selected coordinate system (for example: meters, degrees, or feet).
    • Pixel Size: Enter the X and Y pixel size in the same units as the selected coordinate system (for example: meters, degrees, or feet).
    • Image Size: Enter the number of Columns and Rows in the grid.
    • Tie Point: Enter the Pixel X/Y coordinates of the upper-left pixel location in the grid. Enter the corresponding Map X/Y coordinates for this pixel location, in the same units as the selected coordinate system.
  4. Select the resampling method to use:
    • Nearest Neighbor (default): Uses the nearest pixel without any interpolation.
    • Bilinear: Performs a linear interpolation using four pixels to resample.
    • Cubic Convolution: Uses 16 pixels to approximate the sinc function using cubic polynomials to resample the image.
  5. In the Output Raster Series field, provide a filename and path for the output .series file.
  6. Enable the Display result check box to display the output in the view when processing is complete. Otherwise, if the check box is disabled, the result can be loaded from the Data Manager.

  7. You can run the process in the background on your computer or in the background on an ENVI Server (if available). Click the down arrow next to the OK button and select one of the following:

    • Run Task in the Background: Runs the process on your computer. This method does not use an ENVI Server. The job progress will show in the ENVI Job Console's Background Jobs tab.
    • Run Task on envi_server_name. Runs the process on the selected ENVI Server. The job progress will show in the ENVI Job Console's envi_server_name tab.

    See ENVI Job Console for details on monitoring ENVI Server jobs and viewing results. See ENVI Servers for details on configuring and using an ENVI Server.

  8. Click OK to regrid the series.

Regrid Raster Series by Index

This tool creates a common grid that is based on the spatial grid parameters of a selected raster within the series. It regrids the source rasters to the common grid.

  1. In the Input Raster Series URI field, select a .series file for input.
  2. Select an optional Raster Index, which is a zero-based index corresponding to the raster you want to select. For example, the third raster in a series has a Raster Index value of 2.

  3. Select the resampling method to use:

    • Nearest Neighbor: Uses the nearest pixel without any interpolation.
    • Bilinear: Performs a linear interpolation using four pixels to resample.
    • Cubic Convolution: Uses 16 pixels to approximate the sinc function using cubic polynomials to resample the image.
  4. In the Output Raster Series field, provide a filename and path for the output .series file.
  5. Enable the Display result check box to display the output in the view when processing is complete. Otherwise, if the check box is disabled, the result can be loaded from the Data Manager.

  6. You can run the process in the background on your computer or in the background on an ENVI Server (if available). Click the down arrow next to the OK button and select one of the following:

    • Run Task in the Background: Runs the process on your computer. This method does not use an ENVI Server. The job progress will show in the ENVI Job Console's Background Jobs tab.
    • Run Task on envi_server_name. Runs the process on the selected ENVI Server. The job progress will show in the ENVI Job Console's envi_server_name tab.

    See ENVI Job Console for details on monitoring ENVI Server jobs and viewing results. See ENVI Servers for details on configuring and using an ENVI Server.

  7. Click OK to regrid the series.

Regrid Raster Series by Intersection

This tool creates a common grid that is the geometric intersection of all source rasters; it regrids the source rasters to the common grid.

  1. In the Input Raster Series URI field, select a .series file for input.

  2. Select the resampling method to use:

    • Nearest Neighbor: Uses the nearest pixel without any interpolation.
    • Bilinear: Performs a linear interpolation using four pixels to resample.
    • Cubic Convolution: Uses 16 pixels to approximate the sinc function using cubic polynomials to resample the image.
  3. In the Output Raster Series field, provide a filename and path for the output .series file.
  4. Enable the Display result check box to display the output in the view when processing is complete. Otherwise, if the check box is disabled, the result can be loaded from the Data Manager.

  5. You can run the process in the background on your computer or in the background on an ENVI Server (if available). Click the down arrow next to the OK button and select one of the following:

    • Run Task in the Background: Runs the process on your computer. This method does not use an ENVI Server. The job progress will show in the ENVI Job Console's Background Jobs tab.
    • Run Task on envi_server_name. Runs the process on the selected ENVI Server. The job progress will show in the ENVI Job Console's envi_server_name tab.

    See ENVI Job Console for details on monitoring ENVI Server jobs and viewing results. See ENVI Servers for details on configuring and using an ENVI Server.

  6. Click OK to regrid the series.

Regrid Raster Series by Union

This tool creates a common grid based on the geometric union of all source rasters; it regrids the source rasters to the common grid.

  1. In the Input Raster Series URI field, select a .series file for input.

  2. Select the resampling method to use:

    • Nearest Neighbor: Uses the nearest pixel without any interpolation.
    • Bilinear: Performs a linear interpolation using four pixels to resample.
    • Cubic Convolution: Uses 16 pixels to approximate the sinc function using cubic polynomials to resample the image.
  3. In the Output Raster Series field, provide a filename and path for the output .series file.
  4. Enable the Display result check box to display the output in the view when processing is complete. Otherwise, if the check box is disabled, the result can be loaded from the Data Manager.

  5. You can run the process in the background on your computer or in the background on an ENVI Server (if available). Click the down arrow next to the OK button and select one of the following:

    • Run Task in the Background: Runs the process on your computer. This method does not use an ENVI Server. The job progress will show in the ENVI Job Console's Background Jobs tab.
    • Run Task on envi_server_name. Runs the process on the selected ENVI Server. The job progress will show in the ENVI Job Console's envi_server_name tab.

    See ENVI Job Console for details on monitoring ENVI Server jobs and viewing results. See ENVI Servers for details on configuring and using an ENVI Server.

  6. Click OK to regrid the series.

View a Spatiotemporal Series

You can also write a script to view a spatiotemporal series using the ENVIRasterSeriesLayer routine. Use the ENVIView::ChipToVideo method to export an animation to a video file.

  1. From the menu bar, select File > Open As > Series.
  2. Select a .series file that you created in the steps above. Click Open.
  3. See Animate Raster Series and NITF Image Segments for full instructions.

See Also

Working with Temporal Cubes