>  Docs Center  >  Using ENVI  >  SPEAR Vegetation Delineation
ENVI

SPEAR Vegetation Delineation

SPEAR Vegetation Delineation

The Vegetation Delineation tool enables you to quickly identify the presence of vegetation and to visualize its level of vigor. The Wizard also provides tools to facilitate creating graphics for use within reports and briefings.

  1. The Vegetation Delineation tool is intended for multispectral data. If you have hyperspectral data, use the tools described in Vegetation Analysis.
  2. From the Toolbox, select SPEAR > SPEA Vegetation Delineation. The ENVI Vegetation Delineation Wizard displays the File Selection panel.
  3. Click Select Input File, choose a file, then click OK. The input image should be a multispectral file in any format readable by ENVI.
  4. To optionally process only a portion of the scene, click Select Subset. A small Select Spatial Subset dialog appears.
  5. Click Spatial Subset. The standard Select Spatial Subset dialog appears.
  6. By default, output files are saved to the same directory and use the same rootname as the input file, minus any extension. Output files are appended with a unique suffix. To change the directory and/or root filename, click Select Output Root Name.
  7. Click Next. The Atmospheric Correction panel appears.
  8. Perform atmospheric correction. Dark object subtraction produces good results with minimal user input.
  9. When atmospheric correction is complete, click Next. The Examine Results panel appears.
  10. When you are finished examining results, click Next in the Examine Results panel, then click Finish to exit the Wizard.

Examining the Vegetation Delineation Results


ENVI loads a single display group with a natural color composite. This is the reference image.

  1. To change the reference image to a false color composite, select the appropriate choice from the Reference Image drop-down list, then click Load.
  2. Optionally, use Auto-Flicker to examine your results.
  3. To load a vegetation image with a color table applied, select the Color Table tab.
  4. To load a density sliced image with the default parameters, select the Density Slice tab. A new display group opens with the density sliced image. The new display group is dynamically linked to the reference image display group.
  5. When you are finished examining results, click Next in the Examine Results panel, then click Finish to exit the Wizard.

Color Table

  1. Select a color table from the Color Tables list, then click Apply Color Table. A new display group opens with the colorized image. The new display group is dynamically linked to the reference image display group.
  2. To preview new color tables, select the desired color table in the list, then click Apply Color Table.
  3. Use the Stretch Bottom and Stretch Top slider bars to change the way the color table is applied. See the following figure for an example. Move the slider bar positions to reverse the color table order if needed. The following shows the changing color table appearance with slider bars (imagery courtesy of DigitalGlobe).

  4. To save the displayed color table image to a graphics file suitable for use in a briefing or report, click Save to File. The Output Display to Image File dialog appears.
  5. Pixels with no vegetation are masked using the Veg Mask parameter so that analysis is focused on vegetated pixels. Change the Veg Mask threshold if needed. Higher values mask more pixels, lower values mask fewer pixels. You can change the color of the mask by right-clicking the color patch and selecting a new color. Turn off the mask by clearing the On/Off check box. Following is an example of adjusting the vegetation mask by changing the Veg Mask Threshold (imagery courtesy of DigitalGlobe).

  6. To create an output file showing the applied color table overlaid on the reference image, click Create Overlay Mosaic. Pixels masked out with the Veg Mask parameter are transparent, allowing the underlying reference image to show through. ENVI prompts you to select an output filename, then adds the mosaic to the Layer Manager.
  7. To export the overlay mosaic to a graphics file suitable for use in a report or brief, load the image into a display group, then select File > Save Image As > Image File. The Output Display to Image File dialog appears. Following is an overlay mosaic (imagery courtesy of DigitalGlobe).

Density Slice

  1. Select the Base Image to use from the drop-down list, then click Load Image. A new display group opens with the density slice, dynamically linked to the base image type you selected.
  2. There are four display ranges available for use. The default NDVI ranges are general rules of thumb that apply in many, but not all cases. Adjust the ranges to suit your particular data by entering new values or using the up/down arrows. The ranges are as follows:
    • No Veg
    • Sparse Veg
    • Moderate Veg
    • Dense Veg

    The numbers displayed for each range indicate the bottom NDVI threshold. For example, the default for No Veg are pixels with an NDVI value falling between -1.0 and 0.249.

    The Normalized Difference Vegetation Index (NDVI) generates an image that ranges from -1.0 to 1.0. Pixels with no vegetation tend towards -1.0, while pixels with vigorous vegetation tend towards 1.0.

  3. Adjust the color for each range by right-clicking on the color box and selecting a new color.
  4. To turn off a range to show the Base Image beneath it, clear the On/Off check box for that particular range. Following is a density sliced image (left) with corresponding parameters (right) with No Veg range turned Off to display the base image (natural color) beneath (imagery courtesy of DigitalGlobe).

  5. To restore the Density Slice parameters to their original state, click Restore Defaults in the Examine Results panel.
  6. To save the density slice image to a graphics file suitable for use in a briefing or report, click Save to File in the Examine Results panel. The Output Display to Image File dialog appears.



© 2019 Harris Geospatial Solutions, Inc. |  Legal
My Account    |    Store    |    Contact Us