lab 3: exterior orientation using e-foto space...
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PBW 201B | Ground and Aerial Information Systems | Lab 3 Space Resection
Lab 3: Exterior Orientation Using E-foto
Space Resection
Objective
After you performed the Interior Orientation (IO), the parameters needed to adjust photo coordinates
and transform them to a photographic coordinate system (x, y) are calculates. Now, the coordinates
that you measure form the photographs are of a reliable accuracy.
This exercise is intended to introduce you to the process of exterior orientation of images by the
method of space resection. Next lab will be about performing the exterior orientation of a block of
photographs using block bundle adjustment – aerial triangulation. The exterior Orientation is the
process through which a set of control points measured on the ground and in an image are used to
calculate the exterior orientation parameters of an aerial image.
While the Bundle Block Adjustment gives the exterior orientation of all photogrammetric images of a
block, the spatial resection algorithm – the one you are performing today - allows the calculation of
these parameters for each image separately. The exterior orientation calculates the camera optical
center coordinates (X0, Y0, Z0) and its attitude angles (ω, φ and κ) in the image acquisition instant.
These parameters are in the ground coordinate system, such as the Egyptian Transverse Mercator
(ETM) system. The Spatial Resection must be executed separately for each photogrammetric image
in your project: 16, 17, and 18.
Important Note
DO NOT SAVE YOUR WORK DURING THIS LAB. When you are done, call the TA to check your work.
Files needed:
• EfotoGroundControlCoordinates.txt this file includes ground coordinates of control points
in the UTM coordinate system
• GCP_DESC.pdf this file describes the location of the control points
• 1997_016_300dpi, 1997_017_300dpi, and 1997_018_300dpi the photographs
Remember that the photos must be stored in a root directory when using E-foto.
Procedure: طريقة العمل
Step1: Starting the Exterior Orientation
1- Open the Project file: “UERJ_io.epp” by clicking on it. This is a project file of an area in Rio
De Janeiro in Brazil, the file extension (epp) stands for: efoto photogrammetric project . The
interior orientation is already done, click on sensors and check the interior orientation
information, for reference, this information is listed in the last page of this handout.
PBW 201B | Ground and Aerial Information Systems | Lab 3 Space Resection
2- Check that the project file includes the ground coordinates of the control points that you will
measure on the photos. Click on: “points”, if no coordinates are listed, click on “import
“import from text” and select the file “EfotoGroundControlCoordinates.txt”. Now the ground
control point list is displayed.
3- Now, start performing the space resection operation. From the menu bar, select Execute
then Space Resection, choose the image to work on. Start with Image “16”.
Step2: identifying the ground control points on the image
4- Observe the location of the available ground control points (GCP) on each image 016, 017,
018, provided in the GCP_DESC file, open this file to better show the points as you digitize
the points. For this task, you will not use all the points. The table below shows the points to
be used for each photo:
Photo Ground control points to use in space resection points
16 1, 3, 5, 12
17 1, 5, 10, 11
18 2, 10, 11, 14
PBW 201B | Ground and Aerial Information Systems | Lab 3 Space Resection
Photo (16)
PBW 201B | Ground and Aerial Information Systems | Lab 3 Space Resection
Photo (17)
PBW 201B | Ground and Aerial Information Systems | Lab 3 Space Resection
Photo (18)
PBW 201B | Ground and Aerial Information Systems | Lab 3 Space Resection
Ground control point coordinates table
The overlapping area is shown in the GCP_DESC file too
4- Using the GCP_DESC file, zoom in until you find the exact location of point 1 in the image you
work on
5- Upon reaching the location of point 1, Click the SetMark button to mark point 1
PBW 201B | Ground and Aerial Information Systems | Lab 3 Space Resection
6- Repeat the process for the second, third and fourth point until you mark all the points with their
exact location with the help of the GCP_DESC file.
Step3: External Orientation calculation
7- Once you finish all the points, choose the Exterior orientation button.
8- Choose the number of iterations for the calculation accuracy, then press Ok.
PBW 201B | Ground and Aerial Information Systems | Lab 3 Space Resection
9- Choose the parameters precision, then press Ok.
10- Calculation’s result is shown with values corresponding to the Xa vector (E.O.
parameters matrix and its variance-covariance matrix (MVC(Xa))).
The Xa matrix and its variance-covariance matrix
PBW 201B | Ground and Aerial Information Systems | Lab 3 Space Resection
11- La Matrix (adjusted observations matrix) and V (vector of residuals) then are shown.
The V vector
12- Check the results, if the values of (σo ) is less than 0.15 mm, call the TA to mark your work done,
then close the Window, do not accept or save the results.
13- Repeat the process for the other two images.
The information about the images on the main menu
PBW 201B | Ground and Aerial Information Systems | Lab 3 Space Resection
Background:
Interior Orientation parameters: When
you click on “Sensor” on the window to
the left, you are supposed to enter camera
information and interior orientation
parameters. Since for this file, the entirior
orientation is done, the information is
displayed. As shown to the right. Examine
the information and make sure that you
understand the terms