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Earn: 1 PDH, 1 AIA LU/Elective; 0.1 IACET CEU
This course may qualify for continuing education through the NYSED. For more information, visit www.op.nysed.gov/prof/pels/peceques.htm.
This course may qualify for continuing education through the FBPE.
- Define what photogrammetry is and how it originated.
- Define what LiDAR is and how it originated.
- Describe the differences between photogrammetry and LiDAR.
- Identify the different use cases for photogrammetry and LiDAR.
- Cite at least one case where a combination of LiDAR, photogrammetry and/or bathymetry can be used.
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RCEP and AIA course #163645
LiDAR (light detection and ranging) and traditional photogrammetry play a role in nearly all land surveying and mapping projects today. LiDAR has evolved into an accurate, cost-effective method of generating the mass points used to create a digital elevation model. The increases in the accuracy of LiDAR sensors have been impressive, if not astonishing, over the last couple of years. Today’s LiDAR sensor technology allows us to place points on the ground at very dense postings and achieve extremely accurate elevations for these points.
However, aerial photography is still necessary to generate breaklines at abrupt changes in the terrain. These breaklines are normally collected from photography at the edges of roadways and water bodies; at the tops and toes of slopes; along headwalls and retaining walls; and other places in the landscape with sudden changes in elevation. Stereo photography is also used for planimetric feature capture common in large-scale mapping. Typical planimetric features collected in mapping include the edges of roadways, building footprints, driveways, fences, utility poles, group vegetation, sidewalks and drainage features that are easily seen in project photography.
Lastly, photography also serves as the base for digital orthophotography. Digital orthophotos are generated for most mapping projects today to supplement topographic and planimetric mapping. They can be a significant source of information, during planning and design, and serve as a useful tool for communicating with a lay audience that likely doesn’t fully understand more traditional maps (such as at public hearings).
But are breaklines always required for topographic mapping? As data postings from LiDAR become denser, can mass points without breaklines provide an accurate model of the ground? Collected from fixed-wing aircraft (airplanes), data postings from the LiDAR collection used for large-scale projects normally range from one to four points per square meter. Rotary wing aircraft (helicopters) can collect significantly more dense data, but unit costs compared to fixed-wing aircraft are considerably higher due to the slower speeds and narrower swath widths common with this collection. Point densities of 80 or more points per square meter are common with helicopter-based units. At these densities, breaklines provide very little additional information to a digital elevation model. But helicopter-based applications are normally constrained to specialized applications because of the higher unit costs and not employed on typical large block projects like city/county or statewide mapping.
Higher density data will continue to be collected as LiDAR sensors continue to improve, and there may get to a point where breaklines are not as necessary due to the increased density of the mass points available from fixed-wing collection. Yet, for most projects, LiDAR technology is not quite there yet.
Land surveyors and geospatial professionals use photogrammetry and LiDAR (light detection and ranging) in a variety of visual mapping and land survey documentation projects.