Create Spatial and Spectral Image Subsets

来源: https://vis-webcontent.s3.amazonaws.com/quickguides/Process+Raster+Data/Create+Image+Subsets/index.html

Lesson content

Lesson 1 of 1

Create Spatial and Spectral Image Subsets

In this quick guide, you will:

•

Define a spatial subset that limits processing to a specific area. * •

Define a spectral subset that limits processing to specific bands.

Spatial Subsets

Creating a spatial subset in remote sensing imagery involves selecting a specific area of interest from a larger dataset. Here are some reasons why someone might do this:

Focus on a Specific Area: By narrowing down to a particular region, analysts can concentrate on the area of interest without the distraction of irrelevant data.
Data Management: Working with smaller datasets can be more manageable and less resource-intensive, making it easier to process and analyze the data.
Improved Analysis: Subsetting allows for more detailed and accurate analysis of the selected area, which can be crucial for tasks like monitoring environmental changes, urban development, or agricultural practices.
Efficiency: Reducing the dataset size can speed up processing times and reduce storage requirements, which is particularly beneficial when dealing with high-resolution imagery.
Customization: It enables customization of the dataset to meet specific project needs, ensuring that only relevant data is included.
1

In ENVI, click File-> Open. 2. 2

Go to the "data" directory in your ENVI installation path.

Windows:C:\Program Files\NV5\ENVIxx\data (xx is the version number) Linux:/user/local/NV5/envixx/data
Mac:/Applications/NV5/envixx/data 3. 3

Select the file qb_boulder_msi and click Open. The image is added to the Layer Manager and displayed in the Image window. 4. 4

In the main dropdown, select File > Save As > Save As (ENVI, NITF, TIFF, DTED) from the Menu bar. The Data Selection dialog appears. 5. 5

Click the Spatial Subset button. The Data Selection window will expand.

You can specify a spatial subset using the icons above or you can enter specific columns and rows values. For this quick guide, let's manually draw a smaller box focusing on the lake.

6

Left click and hold to drag a new bounding box within the image preview to encompass the lake. Release the left mouse button to create the bounding box. You can adjust the sides and size if needed.

Notice that there is now a definition of the spatial subset to the right of the Spatial Subset button.

7

Click OK in the Data Selection window. 2. 8

Enter a path and filename and then click OK. Your spatial subset image will automatically load in ENVI.

Spectral Subset

Spectral subsetting in ENVI is a powerful tool for several reasons:

Focus on Relevant Data: By selecting specific bands, you can concentrate on the most relevant spectral information for your analysis, which can improve the accuracy and efficiency of your work.
Reduce Data Volume: Hyperspectral data can be very large. Spectral subsetting helps reduce the data volume, making it easier to manage and process.
Enhance Computational Efficiency: Working with a smaller subset of bands can significantly speed up processing times, which is particularly beneficial for complex analyses.
Target Specific Features: Different materials and features reflect light differently across the spectrum. Spectral subsetting allows you to target specific features or materials by selecting the bands where these features are most distinct.
1

In the main dropdown, select File > Save As > Save As (ENVI, NITF, TIFF, DTED) from the Menu bar. The Data Selection dialog appears. 2. 2

Highlight the qb_boulder_msi dataset and then click Spectral Subset. The Spectral Subset window will pop up. 3. 3

Select only Bands 2, 3, and 4 (Green, Red and Infrared).

4

Click OK in the Spectral Subset window. The information next to the Spectral Subset button should now show '3 of 4 bands'. 2. 5

Click OK in the Data Selection window. 3. 6

Enter a path and filename for your spectral subset image and then click OK. ENVI will display the new image. It should appear different than the 4-band image layer.

This concludes the quick guide.

Your input is important to us, please take a few moments to fill out ourQuick Guide Feedback(opens in a new tab)form.