Introduction

This lab has two separate tasks that will let you do DEM extraction using ERDAS Leica Photogrammetry Suite (LPS), which is a softcopy photogrammetry system. In Task 1, you will use the information provided to define a block file for interior and exterior orientations of a set of stereopairs. Task 2 involves the use of a predefined block file to do more complex DEM extraction and orthorectification. The exercise will be done using ERDAS Imagine and LPS. You can find the LPS program from the Windows Start menu (e.g., under Programs -> GIS -> ERDAS 2010 -> LPS 2010 (or ERDAS IMAGINE 2010). This is your opportunity to explore the ERDAS Image software and to get acquainted with the interface. Use the software help system to learn about the different software options and functionality. Type the answers to all questions of both tasks, attach your map, and submit them to the instructor by the due date.

The lab files used in Lab 2 are in the I:\Students\Instructors\Geoffrey_Duh\GEOG4593\Lab2 folder. Please copy both the frame and laguna_beach folders to your lab2 folder in your workspace in C:\Students. The two documents you need for this lab are in I:\Students\Instructors\Geoffrey_Duh\ERDAS Imagine\Imagine10. You will use LPS_PM.pdf (LPS Project Manager User's Guide) for Task 1 and LPS_ATE.pdf (LPS Automatic Terrain Extraction User's Guide) for Task 2. You can print the chapters needed for this lab, but don't print the whole document from lab computers.

Attentions!!!

Due to editing negligence of the ERDAS online documents, you may find discrepancies between the pdf instructions and the actual software's graphic user interface (GUI). Please explore the GUI a little bit. You should be able to find the tools mentioned in the documents.

Task 1. Define a Block File and Perform Orthorectification Using an Existing DEM

Instructions & Questions

Open LPS_PM.pdf and skim pages 20 (Single Frame Orthorectification vs. Block Triangulation) through 60 (up to before Satellite Photogrammetry). Pay attention to the sections of GCPs (pages 51-53) and Tie Points (pages 54-55). Complete the "Frame Camera Tour Guide" tour guide exercises (pages 73 - 137) and answer the following questions. Be extremely careful with the numbers you key in. Make sure they match the numbers in the Tour Guide. If would be very helpful, if you keep track of the information used in this exercise (i.e., what data are required to complete this type of task? Where can you get the data?) Also, whenever you specify an output file, make sure it goes to your lab2 folder. If you didn't specify the correct output path, then all output will be saved in the C:\temp\users folder.

Write down the RMSE of your fiducial (interior) orientation for individual images.

On the exterior orientation tab of the Frame Editor, the coordinates of Xo, Yo, and Zo define the position of what feature of the image space model?

Copy and paste the exterior orientation parameters (i.e., Image ID, Xs, Ys, Zs, OMEGA, PHI, KAPPA) from your Triangulation Summary report and submit them with your exercise.

What's the spatial resolution of the DEM (colspr_dem.img) you used to orthorectify the NAPP photos? Hint: Use the Image Information tool in the Tool pull-down menu on ERDAS Imagine's main icon panel to view the image information of colspr_dem.img.

What was the flight direction of the mission that collected the photos you used in this exercise? Use the cardinal directions (e.g., E, W, NE, NW, etc) to describe the flight direction.

Describe what information you will need to orthorectify frame aerial photos using an existing DEM.

Task 2. Extracting DEM

Instructions & Questions

We will use the Classic ATE (instead of eATE) to extract DEM from a predefined block file. Complete the LPS_ATE Tour Guide (pages 23 - 71 in LPS_ATE.pdf) and answer the questions at the end of this document.

LPS_ATE.pdf instruction update:

* If you get a warning about "IMAGINE Viewer background transparency preference is on" when working with ATE, use the ERDAS Imagine preference dialog window (from the session -> preferences menu) to uncheck the background transparent option in the viewer category.

1. One micron equals 0.0001 centimeters. One inch equals 2.54 centimeters. The photos of National Aerial Photography Program (NAPP) are acquired from airplanes flying at an altitude of 20,000 feet using a 6 inch focal length camera resulting in a scale of 1:40,000. To get a ground resolution of 5 meters, what DPI (dots per inch) setting should be used to scan the NAPP photos? What's the size (in microns) of the dots?

2. Use the online manual or the Set Strategy Parameters dialog window in the Area Selection tab in the DTM Extraction Properties window to find the various Search Size settings associated with different Topographic Type. Make a table that lists the various topographic types and their search sizes (both X and Y directions). Explain why the search size varies.

3. What are the X and Y cell sizes of laguna_reference_dem.img?

4. Print and hand in a copy of your DTM Extraction Report. Use the report and the Point Measurement tool to examine all the block tie points that have a residual larger than +/- 5 meters and smaller than +/- 0.5 meters. Describe what kinds of tie points have more uncertainty (i.e., with residuals away from 0) in extracting DEM and what kinds of tie points are more accurate (i.e., with residuals close to 0) for extracting DEM.

5. Use the Ortho Resampling tool on the LPS Project Manager menu to generate an orthophoto for lag12p1.img. Specify lagunadem as the DTM source. Set the output cell size to 10 X 10 meters and use bilinear interpolation as the resampling method. Use ArcScene to make a 3D perspective map of the orthophoto with lagunadem.img as the source of the base heights. You might need to change the Z unit conversion factor (i.e., "Factor to convert layer elevation values to scene units") to a larger number to make the relief more obvious. Submit a screenshot of this 3D perspective map.