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This article explores how to begin a career in photogrammetry, an exciting field combining remote sensing, geography, photography, geometry, physics, statistics, and computer science to create map documents used for a wide variety of applications. Read ahead if you are interested in a career that uses cameras that fly anywhere from hundreds of feet to hundreds of miles above the earth’s surface to develop solutions in engineering, architecture, transportation, forestry, agriculture and countless more industries.
What is photogrammetry?
In its simplest form, photogrammetry is the process of extracting measurements from images. It comes from the three Greek words photo (light), gram (that which is drawn or written), and metry (measurement). Put together, the three words mean “measurements which are drawn out from light.”
By themselves, most photographs cannot be used to extract measurements since the image is displayed in two dimensions. To counter this, photogrammetry relies on the principle of parallax, or the apparent difference in an object’s location when viewed from two different pictures. When enough geometric information is known, such as the location of the overlapping images and the angle between their positions, distortion is removed through a process called orthorectification. The result is an image, or orthophoto, that can be used to make measurements like a map.
What is a photogrammetrist?
A photogrammetrist is someone who produces maps from overlapping images captured through various remote sensing platforms. In the field’s early days, photogrammetrists used a special viewer (known as a stereoscope) to observe two overlapping images (a stereo pair) from an airplane-based camera system. The stereoscope allowed the analyst to view the two images in a way that created a perception of depth; when the images were aligned correctly, the scene appeared in 3D.
Nowadays digital images and computers take the place of stereo pairs, stereoscopes, and human interpretation. Additionally, satellites, helicopters, and drones have joined manned aircraft as potential sensor platforms. Photogrammetric software uses sophisticated algorithms to look through hundreds or thousands of overlapping images and match features. For example, in a suburban neighborhood there are houses, cars, driveways, roads, mailboxes, patio furniture, and many other objects scattered throughout. The software matches pixels from image to image using pixel color values, other data embedded in each pixel, and image location data. This process helps to remove distortion and make a map.
What does a photogrammetrist do?
A photogrammetrist’s tasks primarily involve preparing images for processing and producing geospatial data products, such as orthophotos—geometrically corrected aerial or satellite imagery. They also participate in other steps of the workflow, including flight planning, camera calibration, data collection, and creating secondary deliverables from the orthophoto.
A photogrammetrist’s responsibilities span the entire photogrammetry workflow, from project planning to producing final geospatial data products. These tasks include:
- Flight/project planning: Modern photogrammetry relies on overlapping images. Photogrammetrists guide airplane and helicopter teams on ensuring proper overlap, placing ground control points, and addressing other project-specific considerations.
- Camera calibration: A misaligned sensor can doom data collection efforts. While there are methods for users to calibrate sensors themselves, most companies with sophisticated systems depend on sending the camera back to the manufacturer for periodic calibrations. The photogrammetrist is responsible for being aware of these requirements and ensuring they are met.
- Data collection: Depending on the sensor, a photogrammetrist may be part of the field crew that collects the data. This is particularly true with drone-based systems since they are easier to learn; someone hired to process drone data may also be expected to collect it. Manned aircraft tend to have specialized sensor operators to crew the cameras, but some smaller organizations combine the two roles.
- Preprocessing: Images are edited for color balancing, noise removal, and other correctable defects that can impact the software’s processing algorithms.
- Data processing: Using specialized photogrammetry software like Agisoft Metashape or Terraphoto, the photogrammetrist marks ground control points, tweaks parameters, filters out noise, and defines project boundaries to ensure accurate results.
- Post-processing: After the initial orthophoto is generated, a photogrammetrist has several tasks remaining before the image is finalized. They identify and remove any anomalies or artifacts in the image, split large files into smaller, more manageable tiles, and convert the files to appropriate formats for delivery.
- Derivative data products: While the orthophoto is a crucial output, it is often just the starting point. Photogrammetrists may be responsible for creating additional data products, such as planimetric drawings, land use classification maps, or object identification and counting, to meet the specific needs of the project.
Necessary skills and experience
Routine photogrammetry tasks pull from a number of disciplines that photogrammetrists need to have some knowledge of.
- GIS: The final deliverables are either georeferenced data products or derived from them, so an understanding of coordinate systems, different vector and raster file types and how they work in a GIS is critical. Also, orthophotos are seldom the final deliverable; derivative products are frequently created from the orthophoto in GIS software.
- Geometry (specifically triangulation): Photogrammetry software uses triangulation based on known positioning of images and angles between same features in adjacent images. Internal camera configurations as well rely on geometry when it comes to the relationships between flying height, focal length, pixel size, and other key project parameters.
- Basic survey methods: For orthophotos to be properly geolocated, known ground control points are marked and included in the processing solution. These ground control points are either chosen from already existing photo-identifiable points or collected by a ground survey crew. Photogrammetrists should understand how these points are created and how to troubleshoot projects in case something goes wrong.
- Basic statistics: Data product accuracies tend to be reported using statistical measures.
- Programming: Photogrammetry and GIS software packages are obviously computer-based. Having a programming language or three in your toolkit comes in handy when automating repetitive tasks or tweaking parameters to improve results. In the world of GIS and photogrammetry, Python is particularly useful.
- An eye for detail: Manual editing of the orthophoto takes concentration and attentiveness.
The process of becoming a photogrammetrist
GIS degree and certification programs: Many colleges and universities offer bachelor programs in GIS and related fields. For those who have already completed undergraduate studies, there are numerous options, many of them online, for a graduate certificate or master’s degree programs. GIS programs help their students develop the technical skills necessary in any photogrammetrist’s career.
Develop technical skills: As mentioned before, photogrammetrists spend a lot of time working with different GIS and photogrammetry software packages. For photogrammetry, many companies offer trial versions of their software where users can process data for free so long as they don’t export the deliverables. Organizations such as Open Drone Map provide sample datasets as well. These resources are great for new photogrammetrists to start learning photogrammetry workflows.
Esri’s ArcGIS ecosystem is the most widely used GIS in larger organizations; QGIS is a free, open-source alternative for those who would like to practice the concepts and techniques without paying for Esri access.
Apply for jobs: Aerial survey companies, engineering firms, and government agencies all hire photogrammetrists. Major players in the aerial survey industry, such as Sanborn and Woolpert, are frequently contracted to conduct aerial surveys and deliver geospatial products. Relevant job titles for photogrammetry professionals include photogrammetrist, remote sensing technician, GIS analyst, and GIS technician.
Photogrammetrists salary and job outlook
The US Bureau of Labor Statistics projects jobs for cartographers and photogrammetrists to grow at six percent by 2033, which it claims is faster than average for most occupations. The Bureau also predicts around 1,000 job openings per year in those two fields.
According to three leading websites, photogrammetrist annual salaries range from a low of $48,660 to a high of $101,000, with the median salary hovering around $75,000.
- USBLS: $48,660 – $113,540 ($76,210 median)
- Salary.com: $64,228 – $85,983 ($74,179 median)
- Glassdoor: $57,000 – $101,000 ($76,000 median)
Frequently asked questions
How Has the Practice of Photogrammetry Evolved Over Time?
Historically, a photogrammetrist used stereoscopic imagery to produce topographic and planimetric maps such as the USGS historic topographic map series. Nowadays photogrammetrists use computer software to produce planimetrically-accurate photomaps (orthophotos).
Another application of photogrammetry, which is not explored in this article, is using images to create 3D models. These 3D models have a wide range of applications from conducting visual inspections of assets to creating computer-generated objects for video games and movies.
What’s the best degree for a career in photogrammetry?
Employers are looking for bachelor’s degrees in geographic information systems (GIS), geography, geomatics, and surveying. Some advanced photogrammetrists combine degree programs in other fields relating to computer science and mathematics.
What industries hire photogrammetrists?
Aerial surveyors, forestry and engineering firms, urban planning companies, government agencies, and drone service providers all hire photogrammetrists.
Do photogrammetrists need to know specialized skills like CAD or a specific software package?
Each employer uses different software. It is helpful to know GIS software such as ArcGIS or Global Mapper, and CAD software like AutoCAD or Carlson. Agisoft Metashape is popular, especially with drone programs and smaller manned-aircraft companies. Larger organizations may use Terraphoto, Trimble Inpho, or Hexagon’s Erdas Imagine.
What’s the difference between photogrammetry and remote sensing?
Remote sensing is a broader term that encompasses the collection of data from a distance using various sensors. Besides digital cameras, other sensors include Lidar scanners, methane detectors, and magnetometers. Photogrammetry, on the other hand, is a specific application of remote sensing that uses photographs, typically from digital cameras, to make measurements and create 3D models of the observed scene or object.
What’s the difference between a photogrammetrist and a cartographer?
A photogrammetrist employs digital images to produce an orthorectified image that can be used to make measurements like a map. A cartographer uses multiple sources (including orthorectified images) to draw and design maps that are more user-friendly and oftentimes more aesthetically pleasing.
Is certification required to become a photogrammetrist?
Certification is not required. Certifications are available and helpful for career advancement, although they tend to require several years of job experience. The American Society for Photogrammetry and Remote Sensing (ASPRS) is the most well-known organization in the United States that offers photogrammetrist certifications.
Can photogrammetrists work remotely, or is it an on-site job?
Most photogrammetry jobs require on-site or hybrid work. Those who are part of the data capture teams are also expected to travel to project sites.