What to use to build a Rectified Orthomosaic
 One of the primary products for Survey Mapping is a rectified orthomosaic. A rectified orthomosaic can be used as a background reference for creating 2D planimetric linework in a CAD platform. A rectified orthomosaic is produced from multiple images taken along controlled flight lines at the right amount of front and side overlaps. My series of books on Survey Mapping Made Simple covers all of the details needed to plan missions that will capture the images correctly. It is important to have a good multiple image neat area splicing solution when creating a rectified orthomosaic. The method to create a rectified orthomosaic from the flight data will be different between software platforms. I have used Pix4D and Dronedeploy which does an excellent job in splicing the imagery. I currently use Metashape Pro which has a easy to follow workflow to create a rectified orthomosaic. I have experimented with different settings to see what produces the best rectified orthomosaic. I have used a Sparse Point Cloud which is the quickest method. Any object that is elevated such as a fence, buildings, walls, covered parking structures, etc. will be somewhat distorted and unreliable for producing 2D planimetric linework as shown in the image 1 below. The cleanest method is to use a high density 3D Mesh to control the rectified orthomosaic. This process takes the longest however the elevated structures are much cleaner as shown in image 2 below. The method I use the most is to create the rectified orthomosaic from a Dense Point Cloud as shown in image 3 below. This method takes a while depending on the computer hardware and the number of images that need to be processed. It produces a rectified orthomosaic that is really close to the one produced using a 3D Mesh.
 (1) Orthomosaic using Sparse Point Cloud
 (2) Orthomosaic using 3D Mesh
 (3) Orthomosaic using Dense Point Cloud
 Conclusion What I have discovered is that elevated structures and objects produce a little distortion when creating a rectified orthomosaic no matter what setting are used. The trick is to minimize the amount of distortion. Building overhangs also hide the building walls which makes it difficult to draw the outline of the buildings just using the imagery. Ground survey methods are still needed to verify the amount of roof overhang, the type of utilities, distinguish between storm and sanitary sewer manholes, etc. Not everything can be identified just using a rectified orthomosaic but it does help to eliminate some ground survey that would need to be collected. It also helps with verifying what has been collected with ground survey methods.
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 Unique Surveying Math and Mapping Book Series, Training and Reference Material Study Guides. Open Survey Mapping Study Guide here . Open Surveying Mathematics Study Guide here .
 Surveying Mathematics Made Simple Book Series. One of the biggest hurdles to get through on the FS and PS exams is the surveying mathematics. It takes dedication to study and practice to master the math needed for the exam and throughout your surveying career.  This series of books will provide the necessary tools and step-by-step processes to bring it all together. Each book in this series will build upon the last one to help you to become a true surveying professional.
 Survey Mapping Made Simple Book Series. Almost anyone can learn to fly a drone. Not everyone can truly master the skills that are required to use a drone for aerial survey mapping and get professional results.  This series of books will provide the necessary tools and step-by-step processes to bring it all together. Each book in this series will build upon the last one to help you to become a true professional remote pilot.
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