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