The Rio de Janeiro State University - |The E-Foto Project Tutorial of the phototriangulation module of the integrated version of the E-Foto software. Authoring and editorializing: Patrícia Farias Reolon and Flavio Jose Rodrigues da Silva. Revisor: Luiz Carlos Teixeira Coelho Filho. Coordinator: Jorge Luís Nunes e Silva Brito. Tutorial of the Phototriangulation Module Introduction Photogrammetry aims to the reconstruction of the 3D object-space from the 2D image-space, thus leading to the computation of reliable, indirect measurements of 3D coordinates in the object-space with known precision. There are three types of photogrammetric measurements: from orbital, optical imagery; form airborne imagery, and from close-range photographs. There are also special applications such as the measurements derived from medical imagery. The image-space is formed from photographs taken with forward and side-lap superposition. The forward superposition is necessary for stereoscopic purposes; the side-lap superposition guarantees the connection between strips of photographs. This is mandatory for topographic photogrammetric mapping. The values of those superpositions usually adopted in photogrammetric projects are 60% in the direction of flight (forward superposition), and 20% to 30% in the side-lap direction. Those values can vary based upon technical requirements of a photogrammetric mapping project. Phototriangulation is the technique of computation of least-squares adjustment of the 3D coordinates of the perspective centers of the photographs in the object-space or in any external reference frame. This process also calculates the Euler angles or the sensor attitude parameters for each image of a photogrammetric block of photographs. 3D coordinates of photogrammetric points, those that are measured only in the image- space, are also accurately computed in the phototriangulation procedure. There are basically two approaches for computation of phototriangulation: the adjustment by independent models and the bundle block adjustment procedures. The former method uses a stereo-model as its basic unit of adjustment; the bundle-block adjustment, also known as the multiple spatial resection, on the other hand, considers a light-ray connecting a point in the object-space, the principal point of the camera, and the projection of the point into the image-space, as its essential element for Least- squares adjustment computation. Therefore, a bundle of light rays forms the block of images, which is adjusted in a unique procedure. If a block has only one single image, the bundle-block adjustment procedure is named “spatial resection”. The e-foto software uses the bundle-block adjustment procedure for airborne imagery, taken either from digital frame photogrammetric cameras or from digitized frame, aerial film cameras. Further details are available in SILVEIRA (2004).
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The Rio de Janeiro State University - |The E-Foto ProjectTutorial of the phototriangulation module of the integrated version of the E-Foto software. Authoring and editorializing: Patrícia Farias Reolon and Flavio Jose Rodrigues da Silva. Revisor: Luiz Carlos Teixeira Coelho Filho. Coordinator: Jorge Luís Nunes e Silva Brito.
Tutorial of the Phototriangulation Module
Introduction
Photogrammetry aims to the reconstruction of the 3D object-space from the 2D image-space, thus leading to the computation of reliable, indirect measurements of 3D coordinates in the object-space with known precision. There are three types of photogrammetric measurements: from orbital, optical imagery; form airborne imagery, and from close-range photographs. There are also special applications such as the measurements derived from medical imagery. The image-space is formed from photographs taken with forward and side-lap superposition. The forward superposition is necessary for stereoscopic purposes; the side-lap superposition guarantees the connection between strips of photographs. This is mandatory for topographic photogrammetric mapping. The values of those superpositions usually adopted in photogrammetric projects are 60% in the direction of flight (forward superposition), and 20% to 30% in the side-lap direction. Those values can vary based upon technical requirements of a photogrammetric mapping project.
Phototriangulation is the technique of computation of least-squares adjustment of the 3D coordinates of the perspective centers of the photographs in the object-space or in any external reference frame. This process also calculates the Euler angles or the sensor attitude parameters for each image of a photogrammetric block of photographs. 3D coordinates of photogrammetric points, those that are measured only in the image-space, are also accurately computed in the phototriangulation procedure.
There are basically two approaches for computation of phototriangulation: the adjustment by independent models and the bundle block adjustment procedures. The former method uses a stereo-model as its basic unit of adjustment; the bundle-block adjustment, also known as the multiple spatial resection, on the other hand, considers a light-ray connecting a point in the object-space, the principal point of the camera, and the projection of the point into the image-space, as its essential element for Least-squares adjustment computation. Therefore, a bundle of light rays forms the block of images, which is adjusted in a unique procedure. If a block has only one single image, the bundle-block adjustment procedure is named “spatial resection”.
The e-foto software uses the bundle-block adjustment procedure for airborne imagery, taken either from digital frame photogrammetric cameras or from digitized frame, aerial film cameras. Further details are available in SILVEIRA (2004).
The very first beginning of the phototriangulation module...
After starting the free software e-foto its initial screen will look like figure 1 below. In the main menu we do have the options Project, Execute, and Help.
Figure 1 – Initial screen of the e-foto software.
Beginning the phototriangulation module...
Step 1: For starting the photo-triangulation module we must go to the Project Manager screen, and choose the options Project and Load File. Those actions will permit the user to browsing through the file folders until finding the folder which contains the desired e-foto photogrammetric file (an *.epp file.) The user not familiar with the creation of an e-foto photogrammetric project should see the specific tutorial, available at the E-FOTO web site.
In our current example, we are going to use the epp file named “UERJ_io.epp”. There the user will find the technical information such as the images that form the block; its interior orientation parameters, the forms of the ground control and checking points, etc. Figure 2 shows the screen shot of the opening of the e-foto photogrammetric project file.
/* Patrícia: Há necessidade de corrigir a figura 2, de modo que esteja ressaltado o
arquivo “UERJ_io.epp” e não o arquivo flavio_OI_fototri.epp. Subtituí-la após a
correção*/
Figure 2 – Initial screen of the e-foto project manager showing the selection of the desired epp file.
Example 1: Now we are going to proceed with the phototriangulation of a block of
three digitized-frame aerial images flown above the Maracanã Stadium, located
in the neighborhood of The Rio de Janeiro State University (UERJ) main
Campus. Those images are available in the following address:
Step 3: The Execute command opens the main screen of the phototriangulation module (figure 4.)
Figure 4 – The main screen of the phototriangulation module. Please notice that images 16 and 17 are loaded in the screen.
There are three types of viewports in the phototriangulation main screen (figure 4): two viewports are for over-viewing of the left and right images currently in use, two for performing the measurements of photo coordinates of photogrammetric, checking, and ground control points, and two for the detailed view of measuring areas in both left and right images. Please notice that those viewports are bounded by a yellow rectangle.
The meanings of the labels of the tables contained in the lower part of the main window of the phototriangulation module (figure 4) are listed below: Left Image Points: This table contains the list of points measured in the left image. Going downward in this table, we find the image file name (i.e., 1997_016_300dpi.bmp), the list of points measured in that image (Id), and their pixel (Column, Line) coordinates.
All Registered Points: This table contains the list of points (Id) measured in both images, their type (Ground Control, Photogrammetric, or Checking Point.) Ground coordinates (i.e., UTM coordinates and Height above Sea level) are also listed for each point.
Right Image Points: This table contains the list of points measured in the right image. Going downward in this table, we find the image file name (i.e., 1997_017_300dpi.bmp), the list of points measured in that image (Id), and their pixel (Column, Line) coordinates.
Image Appearances: Given a point selected in the previous tables, this table shows the list of images where this point was measured (where it appears), as well as the respective pixel coordinates in each image.
After finishing the photogrammetric measurements it is time to indicate the fight direction for each image of the photogrammetric block. This step is necessary for calculation of the initial approximations of the “κ” angles for proceeding with bundle block adjustment. For the sake of exemplification, let us do it for images 16 e 17. For
doing so the user must click on the button and the window Flight Direction will be opened accordingly (figure 5). By default, the checkmark that indicates if the flight direction for a specific image is set to red; as long as the user sets the flight direction, this checkmark is turned to green.
Figure 5 – The Flight Direction window for input of initial approximation of the “κ” angle for each image of the photogrammetric block.
To insert the fight direction for a specific image, the user could either by moving the dial using the left button of the mouse, or by inputting the numerical value in degrees, in the appropriate box. The click in the Accept Angle ending this procedure; after finishing inputting the approximate flight direction angle for every image of the block,
the user must clicking in the Finish button. Only after this clicking the button will be updated, indicating that the bundle block adjustment can be computed.
In a common photogrammetric working flow the user may need to include some (let us say 6 to 12) photogrammetric points in each image of the block. Those points shall be strategically located, such that they can act either as tie points, connecting one image to its neighbor, forming strips of photographs, or as passing points, thus connecting the strips to each other, thus assembling the whole block of photographs. In this hypothesis it will be necessary to go to the point insertion mode. For doing so, the user must click
on the icon. There are some buttons designed to facilitate the phototriangulation
point measurement procedure. The icons of those buttons and their functionalities are presented and explained below:
Button DescriptionEnables new measuring points in photogrammetric images.
Moves the image within the screen space, cranking up the left mouse button.Specific Zoom in active image, by clicking the left mouse button and dragging the mouse over the region.Antialias (slightly blurs the image).Enables performing identical movements in the two images.
Runs the "Zoom" in the same proportion for both images.
Percentage desired zoom image to the left (upper box) and the right image (lower box).return to the initial zoom only in the left picture.
return to the initial zoom only in the right picture.
return to the initial zoom for both pictures.
Step3: Before we select the direction of flight, and execute the phototriangulation, it takes us to determine the location of the control points and photogrammetric points in 3 images. For this we must simply locate the button through the respective points on the images in which they are present. Having performed this step, the following interface below will be obtained, as shown in Figure 6.
Figure 6 - Screen with control points and photogrammetric measured.
Step4: Now we can run the phototriangulation itself. To do so, click the button and the window and fotoFotoTRI-opensas shown in Figure 7 below.
Figure 7 - Screen with available data and selected for implementation, as well as to define the parameters of adjustment.
You can now select which images will be part of the block of images to be processed and points which will be part of the calculations of phototriangulation. You can perform the motion picture Images Available to Selected Images by clicking on the button and moving the entire set, or the button and moving a selected image. To include an image that is at first off the block or otherwise, of Selected Images transfer them to Images Available through the movement button or to repeat this process for all the images, use the button. The same is true for the points. By moving Points Points Available to Selected. If we want to reverse that with what is Available for Selected and vice versa simply clicked the button. Finally confirmation for processing phototriangulation can also set the number of iterations to achieve convergence. This is accomplished through thecombo interations Max as well as the precision values for convergence in meters, through the combo Metricconvergency Angularand value through the combo AngularConvergency. Following chosen images, the points and set the parameters for the maximum number of iterations and the convergence metric and angular must click on the button as we do in this example. However, if you do not want to carry phototriangulation right now, just click the button. After pressing the button, you have the option of calculating the phototriangulation topocêntrico place in a system, if one accepts the option by clicking Yes,as shown in Figure 7b below.
Figure 7b - Screen with option to perform calculations in a system topocêntrico site.
Step5: After we execute the phototriangulation, the window shown in Figure 8 below, where we can observe the results, evaluate them and, if necessary, rerun phototriangulation new parameters for maximum number of "iterations" and metric and angular accuracies of convergence.
Figure 8 - Screen with results phototriangulation the environment and photo-integrated.
Figure 8 we can observe the indicators of the quality of the adjustment of phototriangulation, namely:
Iterations: Number of iterations in the adjustment block converged, according to pre-established tolerances.
Converged (yes / no): Indicates whether the adjustment block converged or stopped because the maximum number of iterations has been reached.
RMSE: Indicates the value of the mean square error of the coordinates of waste Control points being expressed in millimeters.
At the central part of Figure 8 are listed IDs (numbers) and the coordinates of terrain points calculated for the photogrammetric as well as their respective residues.
At the bottom of Figure 8 has The possibility of accepting or discarding the results of adjustment of phototriangulation.
meaning of each of the columns shown in Figure 8 is presented in Table 1 below.
Button DescriptionImage Id Identifierimage
w (Omega) or attitude angle of rotation System image around the X axis
Phi attitude angleor image rotation system around Y axisK rotation angleof the system image around the Z axis angle
coincident with the direction of flight photogrammetricXo X coordinate of the center of perspective Yo Y coordinate of the center of perspectiveZo Z coordinate of the center of perspectiveDw residue adjusting the angle omega
Dphi residue adjusting the angle phiDk residue adjusting the anglekappa
DXO of adjustmentresidue coordinate XoDYO residue adjustment coordinate YoDZO Residue adjusting the coordinateZo
Id pointIdentification of photogrammetricis Thiscoordinated (UTM)N coordinate Northern(UTM)H orthometric altitude or height in the system adopted for the
adjustmentresidue of the adjustment coordinate DN
and residue adjustment coordinateNdH residueadjusting the coordinated H
Figure 8 - Table 1
Step6: in order to save the results in phototriangulation "kml" format and visualize in GoogleEarth, just click the button on the main screen of phototriangulation. Then a window will appear for you to choose the file name you want to record in "kml" format, as shown in Figure 9 below. Then look for the directory where you saved the file and double-click it. If you have Google Earth installed on your screen appear the respective perimeters of the orthogonal projection of each image on the ground (bottom image) of your project and photogrammetric control points and photogrammetric referenced by Google Earth, accordingfiguremostar 10 tofollow.
Figure 9 - Screen to save the file in the format "Kml" (the Google Earth viewer.)
Figure 10 - Screen of the Google Earth viewer with points used in the processing of phototriangulation (represented by green values) as well as the visualization of footers of photogrammetric images of the project (represented by purple lines.)
Note: If the results window is closed and if you want to review the results of phototriangulation, just click the button on the main screen will appear phototriangulation and a new results window, as shown Figure 11 below.
Figure 11 - Results phototriangulation.
Once accepted the results of the adjustment fotoriangulação all images used in adjusting the block will have their values of exterior orientation parameters saved in the project file and recorded in the respective forms of image .
