ZAMORA_ELIAS_GEOMATICS_LAB1

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 Lab Teaching Assistant Emmanuel Atwaki (eatwaki@purdue.edu) Assignment date: 01/10/2024 Submission date: 01/21/2024 Purdue University Lyles School of Civil Engineering CE 203 – Principles and Practice of Geomatics Photogrammetric Cameras, Visual Perception, Film Development, and 3D Reconstruction 1212 1121 – HAMP Software Floors Elias Zamora (zamora14@purdue.edu) SPRING 2024

CE 203 – Principles and Practice of Geomatics Lab–1: Photogrammetric Camera, Visual Perception, Film Development, and 3D Reconstruction Objectives  Demonstration of analog photogrammetric cameras,  Practice stero viewing using mirror and pocket steroscopes,  Confirm the understanding of color film development, and  Image-based 3D reconstruction using Pix4D. Given Data : No Given Data The following sets of data are available .... 1. General (if needed) The general procedure can be outlined as follows: ... Part A: Demonstration of an Analog Camera The basic components of a camera include:  Lens: collects light and brings it to focus at the image plane  Aperture: an opening that controls the amount of light entering the camera  Shutter: opens to expose the film or digital sensor to light, thus determining the period of exposure  Light Sensitive Media: Film or array of pixels that interacts with light to form an image  Body: the light proof housing of the camera mechanism The set-up these camera components, among many others, are shown in Figure 1. The TA will demonstrate the basic components of an Analog Photogrammetric Camera (RC10). The lens cone assembly, Fiducial Marks, and film magazine will be the main emphasis of this demonstration. 2

Part B: 1. Using the furnished mirror stereoscope align the stereo pair of aerial photographs until you see them in 3D. Describe the steps you followed. a. We did not do this in class. 2. Using a pocket stereoscope, view the following stereo pair and order the circles based on the elevation of the outer rings. Start with the highest ring. a. The order of rings 7, 5, 6, 1, 4, 3, 2, 8. The fourth one is the only one I had trouble getting into the order. The rest were easy to figure out and visualize. 3. Using a pocket stereoscope view the following stereogram then write the “question & answer” your can visualize. a. Using the stereoscope, I was able to see a question which was, “What did Danial send first?” The answer to this question is: An email. 4. The highest letters in the above stereo-pair form a sentence. Write the sentence down. a. The pair of symbols made out a sentence: You have a normal degree of stereoscopic perception Part C: Film Development ( 10% - extra credit ) For the given object and film, illustrate the processing steps in the following cases: 5. A negative color film: a. The exposure of film to light creates a Latent image in the film. This happens when the bond between the silver and the bromide of a Silver Bromide crystal is broken by the interation of a photo of light. i. There are “bright,” “intermediate,” and “dark” portions of photons. It goes from left to right in that order. b. The film then gets rid of the bromide from the film, and keeps the silver. i. The latent image develops in that stage. The photons also get their color by use of the Cyan, Magenta, and Yellow Filters. c. The unaffected crystals of silver bromide are turned into salt, which can then be dissolved in water, similar to a “red room” like we see being used in the movies. Then the affected crystals are kept and turned into complamentary colors. 3

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6. An inverse color film: a. Similarly to a negative color film, exposure of light onto the film breaks the bond between the silver bromide crystals when a photon hits them. b. The affected silver bromide crystals are released, with all the unexposed crystals remain kept in the film. i. This process is called “bleaching” of the latent image c. We get rid of the yellow filter, and the silver crystals that have been not been affected get dyed with the complamentary colors. Part D: Image-Based 3D Reconstruction (80%): In this part of the lab, you are given a set of images that you will use together with Pix4D SW to practice 3D reconstruction from a set of overlapping images. The SW is available on the systems in HAMP 1212 and HAMP 1121. You have access to a set of 26 images, which have been captured from 6 flight lines (Figure 2 illustrates the covered area, flight lines, and the list of the images you will be working with). (Figure 2: Illustration of the covered area, flight lines, and the image list for 3D reconstruction using Pix4D SW.) As a part of the processing, you will need to measure a set of Ground Control Points (GCPs) that have been surveyed with GPS. Figure 3 provides an illustration for one GCP (location with the image as well as the GPS survey process). Figure 3: GCP in an aerial image (top left) and its GPS survey (bottom right). The main requirements for this task include: 1. Initial triangulation of the images in a local frame and generation of a quality report, 4

a. This is an image of the first page of a quality report for the local frame image. The process for inserting the photos into the software were simple. The following image is a list of the original GCP points and locations before editing them: 5

b. 2. Identification and measurement of GCPs to realign the outcome from step 1 in a global coordinate system, a. This is the image of the GCP’s after editing their location to the correct spot. It’s hard to visualize without an image before editing the GCP’s, but using the correct photos 6

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as reference points—along with the knowledge of where the wrong GCP coordinates were—you can make out that the GCP’s were edited, and moved onto their correct spots. 3. Re-optimization of the triangulation process after considering the GCPs, a. The process for re-optimization can be seen here: 4. Generation of an orthophoto and dense point cloud of the covered area by the twenty-six images, 7

a. 5. Visualization of the point cloud in CloudCompare (also available in HAMP 1212 and HAMP 1121), 8

6. Visualization of the generated orthophoto, and 7. Documentation of the procedure, your observations regarding the outcome from the different steps, and any problems encountered during the process. The procedure for this lab was straightforward, as following the instructions was merely a matter of reading the instructions carefully. The outdated instructions were unclear in certain areas, since the Pix4D software has been updated since the time of its writing, but overall I think the Lab went well. I did have one issue with my process however. My first time doing the lab, I didn’t use the correct point locations of the GCP’s that were given when I was adding new GCP points. I made my own points and put them in. I had forgotten that we were given the points and their precise location in a separate document. This caused me to have to come in another day to redo the lab and my work. Once I realized my error, I was a lot faster at completing the lab and was able to understand more. The errors that may occur from this lab are not having all 26 images locked in on the correct location of the GCP. Some of them are off, some of them can’t see it because its behind a building, and others just can’t even look at it within their bounds, meaning you can’t use that image to 9

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triangulate the point. Also, when you zoom in on the image, it pixelates, causing you to guess where exactly the pixel containing the correct point would be. This may also be a random error. The note in Appendix A, which is provided by ECN, explains how you can login into the Pix4D SW. Appendix A: Pix4D Login Instructions All, The Geomatics department has a Pro license for Pix4D Mapper version 2. Accounts created on the Pix4D website, pix4d.com, are version 3 accounts. If you make an account on pix4d.com and begin using the software you will be unable to continue working on version 3 projects on Civil Engineering computers. It is installed in HAMP 1212 and HAMP 1121. These PCs are available to all CE students. Logging into the software: Please login to use the software and then log back out once you are done. This will return licenses back to the pool for others to use. Username: cesite@ecn.purdue.edu Password: CESite01 If you have any questions please contact ECN via purdue.edu/ecn/contactus 10

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