Pushing the Boundaries
Consider this scenario in the not-so-distant past: At the request of a client, a surveyor conducts a property survey and prepares a paper map of the property including its dimensions and improvements. The map, often generated in conjunction with a property transfer or other financial transaction, might contain information that would be useful to adjoining properties and their owners. But when the transaction is complete, the map often ends up in a file folder at the title company; while some cadastral information about the property--ownership, size and encumbrances--is public record, much of the information collected by the surveyor may never be seen or shared.
Fortunately, those days of reception books, paper maps and time-consuming record searches are quickly fading. Recognizing the value of electronic information storage, local, regional and national government agencies are rapidly moving into the digital age. It’s a significant step that has opened the door to an even more important change in how cadastral information is collected, managed and utilized. But a paper document, scanned and available online, offers no more information than the original paper map; its only benefit is ease of access. Even a CAD file, while easy to transport and edit, contains no additional information.
The next stage of the evolution is to change the nature and volume of the cadastral information itself. That change, driven by an increasing number of users and applications for cadastral and land information, is under way across the U.S. and around the world.
According to Matt Delano, business area director for cadastral surveying at Trimble, there is a critical distinction between maps and databases. It requires surveyors who collect and manage cadastral data to think in terms of object-oriented data. Rather than collections of points and lines, cadastral information can be presented as features or objects. “When you deliver intelligent objects, you are providing much richer data content in terms of objects and attributes,” Delano explains. “It becomes much more than a spatial representation of data with the descriptive information such as linework and point codes.”
A fair analogy, Delano says, is collecting GIS-style data with survey precision and detail. The GIS world offers graphical depictions of some very deep relational databases - databases that are built of objects. When these objects become cadastral items such as parcels or other real property, then the opportunity to use and interact with the data grows exponentially. “It’s not thinking so much about improving the quality of the data,” Delano says. “The quality is already good. Rather, surveyors are thinking in terms of delivering intelligent data objects that can go into a larger database. Once there, the cadastral objects can be analyzed, grouped and overlaid with data from other sources and users.”
Implementing an object-style approach to cadastral data management poses a number of challenges. While the new approach touches many parts of the surveyor’s workflow, the changes are easily manageable. The more impressive work takes place on the administrative and database side, where decades (or centuries!) of data must be brought together into a cohesive, consistent body of information.
In addition to changes in the content of the databases, cadastral information is increasingly tied to regional or national geodetic reference frames. The near-term result is more-accurate positioning and easier referencing to other layers in the GIS. In the long term, the common reference frames will aid in retracement and recovery of older boundary information.
Germany has a strong history of land data management, with detailed cadastral records dating back more than 150 years. But even as the old records were scanned into digital forms, the cadastral maps and digital land records remained in separate databases. The issues became more complex as a result of reunification, when it became necessary to reintroduce and modernize the cadastral system in the portions of the country that spent more than 40 years under communist rule.
In 1997, work began to develop a cadastral model that can serve all of Germany’s 16 states. Known by the acronym ALKIS, the new model uses GIS techniques in data management while preserving the high precision required in positioning of property monuments and features. ALKIS uses the same data structure as the German topographical system ATKIS, thereby enabling direct interaction between cadastral and topographic information. A third information system, AFIS, manages data on Germany’s geodetic control stations. Driven by the Surveying Authorities of the States of the Federal Republic of Germany (AdV), the AAA initiative brings these systems together into an integrated information model. By mid-2012, roughly half of Germany was running under the ALKIS system, including the states with the largest populations. Work to implement ALKIS in the remaining states may continue into 2013 or 2014.
Defining the ALKIS database proved to be a formidable task. While a single structure for the ALKIS model is required, it’s also crucial to retain the existing information from each state. Despite a fair level of standardization (in coordinate systems, for example) the states had differing requirements for collecting, managing and reporting on cadastral data. To handle these challenges, ALKIS is defined to support ISO standards for spatial and cadastral information as well as feature cataloguing. While the local standards have been preserved, moving onto a new cadastral system is not a simple task for the German surveyors.
A major part of the transition has fallen to the field and office software packages serving the German market. From its headquarters in Braunschweig, HHK Datentechnik GmbH develops geomatics software to support German surveyors in cadastral and other applications. HHK Technical Support Manager Norbert Sperhake has helped develop and test the new field and office software needed to streamline the process of collecting and preparing data for the new ALKIS database. Sperhake says that the effects on local surveyors are manageable. “The survey companies are trying to reduce the effects of the change on the field surveyors,” he says. “The local regulations and procedures won’t change much. There are some changes to names of some attributes and values, but that is generally easy to manage.”
One key change is in the coordinate projection system. The earlier cadastral positions operated in the Gauss-Krüger coordinate system, a three degree-zoned UTM that covered the entire country. Under ALKIS, coordinates are developed in the ETRS89 system, which uses six-degree zones. Sperhake notes that numerous discrepancies have been discovered in points using the older Gauss-Krüger coordinates. But since thousands of existing points will be remeasured in ETRS89, the volume of data will help develop a set of transformation parameters that lets old points be expressed in the new coordinate system. “It lets surveyors migrate older points to the new system with confidence, even if they have not been physically measured in the new system,” Sperhake says.
While accurate coordinates are important, the benefits of ALKIS extend far beyond the technical surveying aspects. Sperhake explains how the field surveyor contributes to the broader utilization of the cadastral data. During construction of a house, a surveyor would collect the position of the structure as usual. But to meet ALKIS requirements, the surveyor will also record the address, type of construction (wood, brick, etc.) and number of stories. The surveyor might also note ownership information and the number of families living in the building. Photos and other notes may also serve to supplement the field measurements.
Gathering information for ALKIS--or any detailed cadastral project--requires the field crew to follow specified procedures for measurement to ensure that positions meet specified accuracies. To optimize productivity, field software can guide crews through field procedures and check results on site.
Sperhake describes how software running on Trimble field controllers assists field crews. The Trimble software can manage points in both the Gauss-Krüger and ETRS89 coordinate systems. If there is a discrepancy between a measured distance and the distance computed from coordinates, the software can determine if the problem comes from a field error or from differences between the two projections. “The distance in nature is the same, but the distances in the databases and projects may be different,” he says. “The surveyor can resolve the issue immediately in the field.”
In collecting data for ALKIS, field crews must use defined codes and descriptors for features and attributes. The lists can be daunting; for example, the feature “building” brings up a list of more than 220 building types ranging from single-family homes to museums, churches, hospitals and fishing cabins. To assist in this process, survey system developers have created field systems tailored to cadastral applications. Delano describes how surveyors use Trimble Business Center software to define feature code libraries that guide the field crews in collecting the needed information. The libraries can be used by Trimble Access field software on all Trimble survey field controllers and also on Trimble handheld GIS data collection field equipment. The survey field data is downloaded into Trimble Business Center, where the measurements are analyzed and adjusted as necessary. The results can then be transferred to cadastral and land information systems using shape files or a number of standard or user-definable formats.
The increased detail in cadastral surveys is affecting the choice of field hardware, according to Delano. While the handheld format of the Trimble TSC3 is very popular, the attribute-intensive nature of some cadastral or topographic surveys is a good fit for the larger display of rugged tablets like the Trimble Tablet PC. But Sperhake doesn’t see surveyors running out to buy new field controllers. “If they change their controller, it’s usually when they buy new or updated instruments,” he says. At that point, the decision on format (handheld or tablet) will be based on the type of work they do.
The benefits of the broader cadastral information are clear, especially when it is integrated into regional land information systems. In many areas, county or municipal governments utilize Web Feature Services to provide a simple user interface and enable the general public to access GIS data. In Boulder County, Colo., the GIS provides a graphical overview of the entire county. Users can use the interactive map to quickly navigate and zoom into individual parcels. From there, it’s easy to link to data on ownership and tenure, zoning, floodplains and similar information. The GIS includes links to survey plats, and also assists in emergency response and wildfire mitigation and recovery. Cindy Braddock, business analyst and GIS manager for the Boulder County Assessor’s office, says that the GIS provides an important tool for appraisers in setting values for real property. It allows people to access sales histories of nearby properties and to correlate values based on location and features.
The interoperability of cadastral information within the GIS also extends its value. For example, in planning an effective system for distributed solar energy, surveyors gather information on the location, orientation and ownership of buildings. In addition, airspace rights and solar access easements can be attached to parcels and buildings. This cadastral information is used in planning and design of the solar panels. Once a system is operating, the data from the surveys can be used to develop highly granular data on the performance of the solar systems.
Additional benefits come from overlaying information onto the individual cadastral objects. For example, if the definition of a flood plain is revised, it can affect a number of parcels. Using overlay functionality, each parcel object is automatically updated to move it into or out of the flood plain--without the need to individually edit each parcel. Conversely, a change in zoning or special use permit can be implemented on a single parcel without affecting the zoning on surrounding properties.
As the cadastral databases mature, they can help improve the GIS overall. In many countries, the field data is collected directly into national or regional projected coordinate systems. This helps resolve conflicts or confusion on the ground, simplifying the work of bringing survey data into a GIS. In the U.S., it is less common for surveyors to work in a projected system. GNSS networks and continuously operating reference stations (CORS) are helping to change this--the accuracy and ties to state plane or other coordinate systems can help increase the positional accuracy of other layers in the GIS.
While the new cadastral systems offer important business opportunities to surveyors, they come with some interesting challenges. The systems can increase the volume and complexity of data that surveyors must collect and manage while maintaining the required levels of accuracy and precision. The value of the cadastral information can also translate into additional revenue for the increased work. This demands an increase in productivity and efficiency in the way surveyors operate in the field and office. “Collecting information for the new cadastral systems is a blend of workflows for surveying and GIS,” Sperhake says, “and field data collection is the key to accuracy and profitability. The most effective firms will have surveyors in the field and office who can operate in both modes. “
Additional information about Trimble equipment and software is at www.trimble.com.
The 3D Cadastre of CondominiumsFrom her office in Boulder County, Colo., Cindy Braddock is working to take cadastral data to the 3D level. She’s developing methods for describing condominiums in the county GIS using graphical 3D models of condo units. The result is a 3D depiction of a condo unit and its relationship to the surrounding units and properties.
The 3D models are created by digitizing 2D information from condominium plats developed by licensed surveyors. Floor elevations are added to produce 3D models; the elevations are tied to the county height datum. The models then become part of the county GIS and can be visualized using Esri tools. Braddock envisions surveyors creating 3D condominium data that could go directly into a GIS or cadastral database. Simple visualization tools can assist surveyors, owners and buyers in understanding the condominium units and common spaces.
Braddock noted that county planners already use 3D models in studies of height limits, view corridors and solar access. The planners use Trimble SketchUp to create and manipulate models to analyze the impact of new structures on the surrounding neighborhoods.