2.3 PPP, VRS Networks, Monumentation, and Land Development

Beyond static and RTK

The NCEES outline lists GPS/GNSS including satellite constellations, static GPS, RTK, PPP, and virtual networks. Section 2.1 covered static and RTK; this section adds PPP and VRS, then monumentation and land development.

Satellite constellations

Modern receivers track multiple Global Navigation Satellite System (GNSS) constellations: GPS (United States), GLONASS (Russia), Galileo (European Union), and BeiDou (China). Tracking more constellations improves satellite geometry, lowers the dilution of precision, and helps in canopy or urban canyons. The professional consequence on the exam is reliability, not brand loyalty.

Precise Point Positioning (PPP)

PPP computes a precise absolute position from one receiver using precise orbit and clock products rather than a nearby base. Its advantages are global coverage and no local base station. Its limitations are a long convergence time (often tens of minutes to reach centimeter accuracy) and sensitivity to signal loss, which forces reconvergence.

Virtual Reference Station (VRS)

A VRS is a network RTK technique. A network of permanent reference stations (often CORS) models atmospheric and orbital errors across a region. When a rover reports its approximate position, the network computes corrections as if a base stood right next to the rover, a synthetic or virtual station. This keeps RTK accuracy consistent over long distances where a single base would degrade. The exam point: VRS reduces baseline-length error growth and gives repeatable coordinates tied to the network datum, provided the rover stays inside the network coverage.

Monumentation standards

A monument marks a corner or control point. Monumentation standards address durability, identifiability, and description. A set monument should be a durable marker (iron rod, pipe, concrete with cap) appropriate to conditions, carry the responsible surveyor's identification (cap or stamp) as state rules require, and be described in the record so a future surveyor can recover and verify it.

Monumentation rules to remember:

• Set monuments that will survive normal site activity and weather.
• Identify the monument so it can be tied to the survey of record.
• Reference it with witness ties so it can be replaced if disturbed.
• Describe type, size, cap, and condition in the field notes and on the plat.

A neat coordinate is not a substitute for a recoverable, identified monument when state law or the deliverable requires one.

Land development solutions

Land development is where measurement meets regulation. NCEES lists regulatory land development criteria, construction criteria, and implementation procedures. A surveyor supporting development must integrate the boundary with the rules that govern what can be built:

The development workflow typically moves from boundary and topographic survey, to a development concept that fits zoning and drainage, to a recorded plat with dedications and easements, to construction layout, and finally to as-built records. A defensible exam answer respects the ordinance and documents constraints early rather than after design is locked.

Consistency across methods

A single project may mix static control, VRS topo, and PPP checks. They will only agree if the datum, realization or epoch, projection, geoid model, and grid-to-ground treatment are consistent. Mixing a network coordinate at one epoch with a PPP solution at another, or comparing grid to ground distances, produces apparent error that is really a reference-frame mismatch.

GNSS error sources to recognize

The exam expects you to know why a GNSS position degrades, not just how to push a button. Major error sources: multipath (signals reflecting off buildings, water, or vehicles), ionospheric and tropospheric delay (mitigated by dual-frequency receivers and modeling), poor satellite geometry measured by dilution of precision (DOP), cycle slips when a signal is briefly blocked, and a false fix where the receiver reports a fixed solution that is actually wrong.

A fixed RTK solution is not proof of accuracy; an independent check at a known point is. Tree canopy, narrow streets, and proximity to large reflective surfaces are the classic field conditions that produce bad fixes.

Initialization, occupation time, and redundancy

RTK and network RTK require a successful initialization (ambiguity resolution) before positions are trustworthy. Best practice is to occupy each critical point for several epochs, then reoccupy after a re-initialization or at a different time of day to change the satellite geometry. Two independent occupations that agree give confidence; a single shot does not. For PPP, the long convergence means short occupations are unreliable, so plan the session length to the accuracy required.

Monumentation: durability matched to purpose

Monument choice should match the point's purpose and lifespan. A primary control monument may be a deep-driven rod with a sleeve or a concrete monument with a disk, set below frost and protected from disturbance. A property corner is often a capped iron rod or pipe. A temporary construction point may be a hub and tack. The principle: the more important and long-lived the point, the more durable and protected the monument, and the more complete its reference ties. Always describe the monument set so the next surveyor can identify it as yours and recover it.

Land development sequence and the surveyor's integration role

The surveyor sits between the regulatory framework and the physical ground. In a typical development, the boundary and topographic survey define what exists, a concept plan is tested against zoning, density, setbacks, drainage, and floodplain rules, a subdivision or site plan is approved and recorded, construction layout builds it, and an as-built records the result.

At each step the surveyor checks that the design respects recorded easements, covenants, rights-of-way, and the ordinance. Catching a setback or drainage conflict during the survey-and-concept phase is far cheaper than discovering it after construction, which is why the exam rewards early constraint identification and documentation.