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We’re experiencing a technological growth spurt. Again. Imaging has always been an important part of surveying. Sketches, diagrams and photographs have long been part of surveyors’ records. Today, the use of imaging technology rapidly is changing the way surveyors work in the field. With the emergence of digital cameras, surveyors routinely collect images at low cost, using digital photos to collect and manage reference information and details.
Today, it’s common to find survey crews equipped with some form of digital camera. It may be a separate device, a smartphone or—increasingly common—integrated into a rugged field computer or handheld controller. Imaging technology is making its way into field instruments as well. Spatial stations, 3D scanners and a growing number of total stations are equipped with integrated video systems. The change is affecting not only surveyors; broad arrays of geospatial disciplines are seeing rapid growth in visual information. GIS data collection, mapping, monitoring and stakeout use photos to supplement written and digital data.
Given the nearly ubiquitous presence of digital cameras, it’s no surprise that we are seeing more photos from survey sites. But while having a camera in a surveying instrument is important, it’s only part of the job. The bigger news has come from the office, where desktop software is quickly bringing the power of imaging technology into mainstream survey processes. To understand the value that imaging brings to the complete survey process, we need to see how imaging data can be managed and utilized to enhance the surveyor’s services and deliverables.
For example, it’s common to take photos of markers, job sites and features needed to document a project. Field crews use cameras in their instruments or field controllers to capture and store the images. In many cases, these images are downloaded—along with other job information—with the image files linked or referenced as an attribute to given points in the project. Modern desktop systems handle the file management automatically, storing images in job directories and ensuring that the appropriate images are attached to a given point.
This automation helps manage large datasets, but doesn’t take full advantage of the large amount of information that is inherent in each photo. While the images can be viewed and shared, they have the potential to be an even more effective part of the office workflow. Filling this gap requires some new approaches to desktop software.
Using imaging for surveying requires field images to be correctly aligned with measured survey points. Accurate alignment enables office technicians to create the same view that the survey crew had in the field. Calibrated cameras and georeferencing ensures that survey data such as points and observed vectors can be accurately overlaid on the images. The office technician can then review the field work to confirm that the required features and measurements were collected. Gaps or blunders can be quickly identified and—as we’ll see soon—corrected in the office.
Some field instruments can automatically turn horizontally and vertically to capture multiple images to produce a panoramic view of a project. Because the camera is in a different position for each image it captures, the office software must resolve and correctly align the individual images into a single panorama. This calls for the office software to have a deep “understanding” of the field imaging systems. As one example, Trimble Business Center (TBC) software used in conjunction with Trimble instruments equipped with Trimble VISION technology makes it possible to efficiently develop realistic panoramic images. The software automatically corrects for data parallax and can balance exposures to provide more even lighting and focus. The resulting panoramic view is an excellent tool for helping clients and stakeholders visualize a site or structure. The panorama provides a good overview of the project as well as detailed visual data on features and conditions.
Field imaging also provides the raw data needed for basic photogrammetry. This is done by utilizing an instrument’s calibrated, georeferenced camera. Let’s say we need to measure an object that is difficult to access even using direct reflex measurement. To take the measurements, the field crew simply needs to use Trimble VISION to capture images of the object from two or more different perspectives. In the office, the technician can view the images in TBC and select the object as it appears in each of the images. The software’s virtual telescope lets the technician select specific pixels in each image. The software then computes the 3D coordinates from the photogrammetric observations.
This process is fast and simple. Office technicians can use photogrammetry to select and compute any number of discrete points. Each new point can be assigned a point identifier, feature code and attributes. With this technique, the surveyor can achieve the long-sought goal of the “survey in the office.”
It gets even better. Surveyors can collect field-measured points to provide control or ground truth for the photogrammetry computations. As a result, surveyors will have good confidence in understanding the precision and accuracy of the office-measured points.
The photogrammetric approach is an ideal solution for complex or difficult objects. For example, instead of trying to measure all the fixtures on a cellular tower, the field crew needs only to capture a few images and measurements to obvious features on the tower. With this data in hand, the bulk of the measuring can be done at the desktop. There are many more applications for terrestrial photogrammetry, including surveys of transportation structures, building facades, earthwork volumes, and oil and gas facilities. At NASA’s Langley Research Center in Virginia, GIS Analyst Jason Hall used a Trimble VX spatial station to capture images of a building on the research campus. “We’re getting into using photogrammetry with the VX,” Hall said. “We took some photos that we used for door locations. It’s a big help to just set up and shoot a few images.”
Unmanned aircraft systems (UAS) offer significant savings in time and cost for survey data collection. While the small aircraft provide speed and flexibility in field operations, the productivity of the overall process relies on the ability to quickly compile the images to produce actionable information. Traditionally, the work to process dozens or hundreds of aerial images would be handled by powerful workstations and specialized technical staff, which can add time and cost to the deliverables. According to TBC marketing manager Carl Thompson, processing terrestrial images differs from airborne images. “Terrestrial images come from a series of station views with a common point origin,” he said. “These can be quickly tied together to produce georeferenced orthophotos.” In contrast, airborne imagery consists of linked images along the flight path. These multi-station images have different perspectives and require much more processing power.
Today, even the high-end photogrammetric processing required for UAS imagery can be handled using desktop computers and software. The TBC photogrammetry module incorporates sophisticated processing functionality based on Trimble Inpho software to provide mass data management and modeling. Surveyors can collect ground control using GNSS or total stations and then process and adjust the terrestrial data using traditional methods. The photogrammetry module can directly access the ground data for use in registering the images to produce orthophotos, 3D point clouds and surface models.
Thanks to the growth of imaging, surveyors can enhance the variety and value of their services and products. At California-based consulting firm Psomas, imaging has become a common tool. Jeremy Evans, technical director for land surveying and mapping, said that it is common to combine individual points with images and scanning data. The company performs a lot of street and intersection surveys, and the imaging capabilities help keep crews out of the streets. “We can use scanning in the Trimble VX to collect 500 to 600 points per hour, even in busy intersections,” Evans said. “The points are combined with photos, and we can then extract information as needed by the engineers.”
According to Thompson, the imaging and photogrammetry capabilities provided by modern desktop software enable the surveyor to add five new types of deliverables to their services. These include:
- Orthographic images compiled from multiple photos taken using terrestrial or airborne cameras.
- Coordinate points and attributes determined using discrete measurements within the orthophotos.
- Surface models of large or small areas developed using aerial images and photogrammetry.
- 3D point clouds based on aerial imagery and controlled with terrestrial GNSS or optical systems.
- New metadata, which consist of information such as condition, color and the presence or absence of specific features. This new class of data provides vision-based information to augment conventional position and attribute data.
To understand the value of the deliverables, consider applications in mining and landfill management. A landfill may request the surveyor to provide orthophotos and computations on volumes and changes, while a mine will ask for point clouds, 3D surface models and orthophotos to conduct its own volume computations, planning and design. The photos are also useful for jobsite monitoring and tracking portable assets. A series of orthophotos, taken over time, provides strong documentation on the activities and progress on a landfill, mine or construction site.
The surveyor’s value comes not only from the new, photogrammetry-based deliverables. The surveyor can also provide value through services and expertise in utilizing the information. For example, because many clients can’t use point clouds or models derived from imagery, a surveyor can provide additional services in extracting, analyzing and formatting specialized information for delivery to downstream users and software. These services, along with strong tools for presentation and visualization, help the surveyor or geospatial professional develop a solid relationship and deeper insight with the clients and their needs. Evans’ colleague at Psomas, Sean Logal, takes advantage of the combined technologies when working for different clients in performing work as varied as ALTA surveys and pavement deformation studies. “Each client has different skill sets,” he said. “You encounter different types of software depending on whether you’re working with an A&E firm or an architect.” Logal said that output for his A&E clients is typically based around CAD deliverables and surface models, while architects may be able to take the Psomas data directly into BIM.
Logal knows that the ability to utilize imagery, field measurements and design data in a single software package provides a competitive advantage. “After I’ve applied all these new technologies and software, at the end of the day I’ve got a quantifiable and measurable savings,” he said. “It gives me a better way to manage my data flow back and forth from the field and in the office. Those are big things to me.”