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Sector Insights
sectorInsight:.com
Education and Professional Development in the Geospatial Information Science and Technology Community
.com
By Mike Tully, MS, MBA, GISP
Where’s the Ground?
O
ur firm bought another aerial camera the other day. It cost $1,500; weighs as much as an iPad; and uses a 12 megapixel CMOS sensor to produce 4K imagery. Its tiny, plastic lens is similar to the one on your cellphone camera. It flies itself! Eight years ago we purchased two large-format CCD cameras for $2.4M. They each weigh as much as a small woman. The glass, compound lens alone weighs 50 pounds. These cameras don’t fly themselves, must be strapped to a $200,000 manned aircraft and piloted by a certified pilot. We will produce amazing map products with both systems. In less than a decade we have seen computing, sensing, and mapping technologies produce these astounding mapping systems that will literally enable anyone to send sensors into the skies and make maps. The drone mapping revolution has cut loose flying for non-specialists. Anyone can perform remote sensing and mapping that previously was possible only using specialized knowledge and gear. Considered together, this explosion of remote sensing and mapping technology will ignite an explosion of new and beneficial applications. Most have yet been discovered. Millions of people will benefit. But could there be any difference in the quality and accuracy of map products produced from these two camera systems? The answer to that question is: “It depends on the application.”
It seems the skill and knowledge of photogrammetrists has been reduced to an algorithm and written to a chip. Common to all remote sensing systems and mapping applications is the age-old question: “Where’s the ground?” Much of everything that follows the remote sensing of things is determining where the ground is. The sciences of photogrammetry and geodesy have been used to find ground since the
Photogrammetric Engineering & Remote Sensing
October 2016 Layout.indd 757
first cameras sprouted wings. Although drones are still in their infancy, they already possess incredible power and sophistication to fly, take pictures, and map the earth. Bundled mapping software is equally sophisticated. It seems the skill and knowledge of photogrammetrists has been reduced to an algorithm and written to a chip. This enables non-specialists to acquire imagery and make orthophotography and 3D models. But one of the chief values of the “photogrammetrist” was understanding the underlying principles of remote sensing, surveying, and mapping and properly applying them in a given application with a specific tool to produce the desirable product. Determining the exact position of the ground is chief among these skills. But can these applications tell you where the ground is? How confident are you of the position of things in your orthos and 3D models? How is the accuracy of ground position measured? Finding ground is a big problem with drone systems. The typical software bundled with drones enables “singlebutton” orthorectification of imagery. This is achieved by first calculating from the pixels in each overlapping image a digital surface model (DSM). That is, a position (XY) and elevation (Z) is calculated for each pixel and assigned to a point floating in space. A 3D “point cloud” is then assembled using every pixel. The aerial imagery is then mathematically “draped” over this DSM to create a 3D model of all features pictured. But where’s the ground? The ground may or may not be visible in the imagery. We have a picture taken from over things and can only see the tops (and maybe some sides) of things. If the ground is obscured by features like vegetation and buildings, it is not pictured. Hence, the DSM will model the “surface” of things NOT the ground. That’s why it is called a digital “surface” model as opposed to a digital “elevation” model (DEM). A Photogrammetric Engineering & Remote Sensing Vol. 82, No. 10, October 2016, pp. 757–758. 0099-1112/16/757–758 © 2016 American Society for Photogrammetry and Remote Sensing doi: 10.14358/PERS.82.10.757
O ct ober 2016
757
9/22/2016 10:37:17 AM
sectorInsight:.com DEM is the default output from lidar sensors and traditional mapping from aerial photography. Drone software (at least currently) is incapable of producing digital “elevation” models using aerial imagery if the ground is obscured. If obscured, then the location and elevation of the “ground” cannot be known. For many (not all) drone applications this is a showstopper. For applications like real estate photography, infrastructure inspection, and film making, DSMs are not a limiting constraint on producing valued products. But for mapping and surveying applications where the location of the ground is necessary, it is critically important the drone operator understand this limitation of current technology.
line between amateur and
Positional accuracy standards exist. The ASPRS has defined accuracy standards for our profession. There are others. ASPRS is actively developing a certification for UAS operators with the hopes that professional UAS certifications will help consumers of our mapping products in every industry have some assurance that the UAS operators are knowledgeable, competent mapping professionals. Methods to ensure, describe, and test the positional accuracy of the mapping products derived from drones are still important, and perhaps more relevant than ever precisely because drones have made remote sensing and mapping so easy and accessible to the non-professional.
professional remote sensing,
Finding the ground is hard. It is physics.
This is really where the
surveying, and mapping designation occurs. Where is the ground? It is common to meet drone operators that marvel at the high resolution orthos they have produced from their new drones but that had no idea about how accurately features are positioned on the earth. They don’t even know how to determine nor describe that positional accuracy. The drone specifications say “accurate to 5 cm” so they assume everything in their maps are located with that precision. They may have never heard of “ground control” or considered that knowing where the ground is could be important. What is the positional accuracy of my orthophotography or 3D map? How reliably can I reproduce products with this accuracy using this drone? What professional liability do you carry for the positional accuracy of your maps?
Positional accuracy is impossible to know without testing the data. Positional accuracy is impossible to know without testing the data. Testing the data requires the use of ground control points that are precisely surveyed on the ground and visible in the aerial photography. There are no shortcuts (yet!). Professionals understand the limitations of their technology. Non-metric plastic lenses are seriously flawed compared to metric glass lenses. CMOS cameras introduce errors in imagery like the rolling shutter problem that CCD cameras don’t share. Added to technological limitations, the procedures used by mapping technicians to create maps from imagery
758
and DSMs can have significant and measurable effects on the ultimate accuracy of map products independent of the drone manufacturers specifications.
O c t o b er 2 016
October 2016 Layout.indd 758
It separates the amateur from the professional. It is an imperative for our remote sensing profession to communicate standards and best practices to the thousands of budding new professionals enabled by drone mapping technology. The health and safety of the public and the dependability of our drone mapping products and services depend upon knowing where the ground is. Our profession and ASPRS have a tremendous opportunity to attract and connect with these new drone mappers and help them quickly mature into professional mappers that use remote sensing technology competently and can confidently answer “Where’s the ground?” Mike Tully, MS, MBA, GISP, President and CEO of Aerial Services Inc. (ASI) and board member of MAPPS.
Stand out from the rest earn asprs certification ASPRS Certification validates your professional practice and experience. It differentiates you from others in the profession. For more information on the ASPRS Certification program: contact [email protected] visit http://www.asprs.org/membership/certification
THE
IMAGING & GEOSPATIAL INFORMATION SOCIETY
Photogrammetric Engineering & Remote Sensing
9/22/2016 10:38:13 AM
Education and Professional Development in the Geospatial Information Science and Technology Community
.com
By Mike Tully, MS, MBA, GISP
Where’s the Ground?
O
ur firm bought another aerial camera the other day. It cost $1,500; weighs as much as an iPad; and uses a 12 megapixel CMOS sensor to produce 4K imagery. Its tiny, plastic lens is similar to the one on your cellphone camera. It flies itself! Eight years ago we purchased two large-format CCD cameras for $2.4M. They each weigh as much as a small woman. The glass, compound lens alone weighs 50 pounds. These cameras don’t fly themselves, must be strapped to a $200,000 manned aircraft and piloted by a certified pilot. We will produce amazing map products with both systems. In less than a decade we have seen computing, sensing, and mapping technologies produce these astounding mapping systems that will literally enable anyone to send sensors into the skies and make maps. The drone mapping revolution has cut loose flying for non-specialists. Anyone can perform remote sensing and mapping that previously was possible only using specialized knowledge and gear. Considered together, this explosion of remote sensing and mapping technology will ignite an explosion of new and beneficial applications. Most have yet been discovered. Millions of people will benefit. But could there be any difference in the quality and accuracy of map products produced from these two camera systems? The answer to that question is: “It depends on the application.”
It seems the skill and knowledge of photogrammetrists has been reduced to an algorithm and written to a chip. Common to all remote sensing systems and mapping applications is the age-old question: “Where’s the ground?” Much of everything that follows the remote sensing of things is determining where the ground is. The sciences of photogrammetry and geodesy have been used to find ground since the
Photogrammetric Engineering & Remote Sensing
October 2016 Layout.indd 757
first cameras sprouted wings. Although drones are still in their infancy, they already possess incredible power and sophistication to fly, take pictures, and map the earth. Bundled mapping software is equally sophisticated. It seems the skill and knowledge of photogrammetrists has been reduced to an algorithm and written to a chip. This enables non-specialists to acquire imagery and make orthophotography and 3D models. But one of the chief values of the “photogrammetrist” was understanding the underlying principles of remote sensing, surveying, and mapping and properly applying them in a given application with a specific tool to produce the desirable product. Determining the exact position of the ground is chief among these skills. But can these applications tell you where the ground is? How confident are you of the position of things in your orthos and 3D models? How is the accuracy of ground position measured? Finding ground is a big problem with drone systems. The typical software bundled with drones enables “singlebutton” orthorectification of imagery. This is achieved by first calculating from the pixels in each overlapping image a digital surface model (DSM). That is, a position (XY) and elevation (Z) is calculated for each pixel and assigned to a point floating in space. A 3D “point cloud” is then assembled using every pixel. The aerial imagery is then mathematically “draped” over this DSM to create a 3D model of all features pictured. But where’s the ground? The ground may or may not be visible in the imagery. We have a picture taken from over things and can only see the tops (and maybe some sides) of things. If the ground is obscured by features like vegetation and buildings, it is not pictured. Hence, the DSM will model the “surface” of things NOT the ground. That’s why it is called a digital “surface” model as opposed to a digital “elevation” model (DEM). A Photogrammetric Engineering & Remote Sensing Vol. 82, No. 10, October 2016, pp. 757–758. 0099-1112/16/757–758 © 2016 American Society for Photogrammetry and Remote Sensing doi: 10.14358/PERS.82.10.757
O ct ober 2016
757
9/22/2016 10:37:17 AM
sectorInsight:.com DEM is the default output from lidar sensors and traditional mapping from aerial photography. Drone software (at least currently) is incapable of producing digital “elevation” models using aerial imagery if the ground is obscured. If obscured, then the location and elevation of the “ground” cannot be known. For many (not all) drone applications this is a showstopper. For applications like real estate photography, infrastructure inspection, and film making, DSMs are not a limiting constraint on producing valued products. But for mapping and surveying applications where the location of the ground is necessary, it is critically important the drone operator understand this limitation of current technology.
line between amateur and
Positional accuracy standards exist. The ASPRS has defined accuracy standards for our profession. There are others. ASPRS is actively developing a certification for UAS operators with the hopes that professional UAS certifications will help consumers of our mapping products in every industry have some assurance that the UAS operators are knowledgeable, competent mapping professionals. Methods to ensure, describe, and test the positional accuracy of the mapping products derived from drones are still important, and perhaps more relevant than ever precisely because drones have made remote sensing and mapping so easy and accessible to the non-professional.
professional remote sensing,
Finding the ground is hard. It is physics.
This is really where the
surveying, and mapping designation occurs. Where is the ground? It is common to meet drone operators that marvel at the high resolution orthos they have produced from their new drones but that had no idea about how accurately features are positioned on the earth. They don’t even know how to determine nor describe that positional accuracy. The drone specifications say “accurate to 5 cm” so they assume everything in their maps are located with that precision. They may have never heard of “ground control” or considered that knowing where the ground is could be important. What is the positional accuracy of my orthophotography or 3D map? How reliably can I reproduce products with this accuracy using this drone? What professional liability do you carry for the positional accuracy of your maps?
Positional accuracy is impossible to know without testing the data. Positional accuracy is impossible to know without testing the data. Testing the data requires the use of ground control points that are precisely surveyed on the ground and visible in the aerial photography. There are no shortcuts (yet!). Professionals understand the limitations of their technology. Non-metric plastic lenses are seriously flawed compared to metric glass lenses. CMOS cameras introduce errors in imagery like the rolling shutter problem that CCD cameras don’t share. Added to technological limitations, the procedures used by mapping technicians to create maps from imagery
758
and DSMs can have significant and measurable effects on the ultimate accuracy of map products independent of the drone manufacturers specifications.
O c t o b er 2 016
October 2016 Layout.indd 758
It separates the amateur from the professional. It is an imperative for our remote sensing profession to communicate standards and best practices to the thousands of budding new professionals enabled by drone mapping technology. The health and safety of the public and the dependability of our drone mapping products and services depend upon knowing where the ground is. Our profession and ASPRS have a tremendous opportunity to attract and connect with these new drone mappers and help them quickly mature into professional mappers that use remote sensing technology competently and can confidently answer “Where’s the ground?” Mike Tully, MS, MBA, GISP, President and CEO of Aerial Services Inc. (ASI) and board member of MAPPS.
Stand out from the rest earn asprs certification ASPRS Certification validates your professional practice and experience. It differentiates you from others in the profession. For more information on the ASPRS Certification program: contact [email protected] visit http://www.asprs.org/membership/certification
THE
IMAGING & GEOSPATIAL INFORMATION SOCIETY
Photogrammetric Engineering & Remote Sensing
9/22/2016 10:38:13 AM