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Questions and Answers
What is the main advantage of using a mosaic over a plan?
What is the main advantage of using a mosaic over a plan?
What is the primary characteristic of a controlled mosaic?
What is the primary characteristic of a controlled mosaic?
What is the minimum end lap required for mosaic work?
What is the minimum end lap required for mosaic work?
What is the purpose of rectification in controlled mosaics?
What is the purpose of rectification in controlled mosaics?
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What is a characteristic of uncontrolled mosaics?
What is a characteristic of uncontrolled mosaics?
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What is the primary reason for creating a mosaic from individual photographs?
What is the primary reason for creating a mosaic from individual photographs?
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What is the key difference between a mosaic and an orthophoto?
What is the key difference between a mosaic and an orthophoto?
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What is the benefit of using special cameras to photograph large areas from the air?
What is the benefit of using special cameras to photograph large areas from the air?
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What is the purpose of using marked and known ground reference points in constructing a mosaic?
What is the purpose of using marked and known ground reference points in constructing a mosaic?
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What is the end product of constructing an orthophoto?
What is the end product of constructing an orthophoto?
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Study Notes
Photo Mosaics and Orthophotos
Types of Mosaics
- Aerial mosaic: an assemblage of two or more individual overlapping photographs to form a single continuous picture of an area
- Three types of mosaics:
- Controlled mosaic: horizontally controlled by picture points established on the ground, constructed to give both high pictorial quality and good accuracy
- Semi-controlled mosaic: utilizes some combinations of specifications for controlled and uncontrolled mosaics, prepared by using ground control
- Uncontrolled mosaic: prepared by matching image details of adjacent photos, no ground control, no rectification, easier and quickly prepared than controlled mosaic
Characteristics and Advantages
- Mosaics show relative planimetric qualities, whereas objects on maps are shown with symbols and must be limited in number
- Mosaic of large areas can be prepared in much less time and at a considerably lower cost than maps
- Easy to understand and interpret by people without photogrammetry or engineering background
Preparing Photo Maps
- Overlapping photographs are placed down consecutively and stapled to a board
- No height control is used during assembling
- Central portion of a photograph is trimmed away, leaving a small amount of overlap
- Minimum of 60% end lap and 30% side lap is required for mosaic work
Rectification of Photographs
- Rectification process allows for bringing all rectified points to the same scale
- Rectification produces an equivalent truly vertical photograph, minimizing effects of relief and tilt displacement
- Graphical and optical-mechanical methods are used for rectification
Uses of Orthophotos
- Orthophoto: a corrected photograph that has been corrected for tilt and relief displacements
- End product may be a contoured photograph to correct scale containing very small errors of position and height
- Useful in flood control, geological investigations, or irrigation works, where ability to see the areas involved is crucial
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Description
Learn about the concepts and applications of aerial photo mosaics and orthophotos, including their types, advantages, and uses in geographical mapping.