Lab 1: Image Display

Introduction

This lab will get you started with Erdas Imagine.  This is your opportunity to explore the software and to get acquainted with the interface.  Use the help system as well as the field guide to learn about the different software options.  You will learn how to set preferences, display an image, query for pixel information, arrange layers, adjust image contrast, link images from different viewers, use AOIs, and use several raster tools.

Instructions

Open the lab book and skim Chapter 1 within the Imagine Essentials section.  Complete the tutorial exercise and answer the following questions.   The tutorial files may be on the hard drive of the lab computers.  You can also download the tutorial file (lab1.zip) here. You will need to unzip it.

1. Explain how you can set TM preferences under the User Interface & Session section of the preferences editor.
2. Explain three other preferences that you can set that were not discussed in the tutorial.  Use the help tools to understand what they do.
3. What is the difference between the recent and goto options when opening a raster layer?
4. Explain what you are looking at when you display the lanier image using R=4, G=5, and B=3.
5. Display the lanier image several times using different raster options available to you.  Then answer the following questions. 
• Resampling is used to calculate pixel values when one raster grid must be fitted to another. When a raster image is opened, the raster grid defined by the file must be fit to the grid of screen pixels in the Viewer.  All Viewer operations are file-based. Any time you resample in the Viewer, the Viewer uses the file as its source. If you zoom the raster layer, the Viewer resamples the file grid to the new screen grid. The resampling methods available are: nearest neighbor (uses the value of the closest pixel to assign to the output pixel value), bilinear interpolation (uses the data file values of four pixels in a 2 x 2 window to calculate an output value with a bilinear function), and cubic convolution (uses the data file values of 16 pixels in a 4 x 4 window to calculate an output value with a cubic function).  When displaying the lanier image using three different resampling methods what is the difference in the way they look.  You'll need to zoom in on a small area such as one of the bridges using three different viewers.  Explain why each looks the way it does based on the different methods described above.
• What does the fit to frame raster option do?
• Explain what the image looks like when using the no stretch option and why it looks that way.
• Explain the difference between true color and pseudo color images.
6.  Explore the information available in the cursor inquiry box.  In order to understand the different types of information you will need to play with the window and use the help buttons.  Explain the different types of information available to you within this window.  What happens to this information when you move the cursor?
7.  Use the polyline measurement tool to calculate the approximate width of the lanier image in meters.
8. Use the perimeter and area measurement tool to calculate the approximate area of the lanier image.  Note: you didn't use this tool in the tutorial.
9. Explain the different zoom options.
10. How do you think you could use the utility of linking viewers geographically?
11. What is an AOI?  Explain the two different methods you used to create AOIs.
12. For what can the piecewise contrast tool be used?
13. Why does the LUT value of Band 2 change when you do a piecewise contrast adjust?  Does the original data (file pixel) change?
14. When you used the Breakpoint Editor you the LUT is composed of linear segments. Breakpoints are the points at which these line segments meet. A breakpoint represents a change in the slope of the lookup table.  How can you use the Breakpoint editor to manipulate the LUT?
15. Print the soilsreport.txt file.
16. Explain the spectral profile.  What do the X and Y axes represent?
17. Explain the spatial profile tool.  What do the X and Y axes represent?  What sort of information can you deduce when plotting all wavelength bands?
18. Explain the output from the surface profile tool and what significance bands 55, 34, and 2 have in the display.
19. Why might you use the image drape functions in Erdas?