-23- 

 Technology&more

A primary benefit of in-house processing is the ability to 
measure baselines within a project and use them in a net-
work adjustment. Points established using online services 
are computed independently and aren’t directly measured 
against other points in the project. While the long baselines 
to surrounding reference stations carry good accuracy, the 
uncertainty at each point and lack of cross-ties can cause 
problems when tying two interior points together. Because 
of the convenience of online services, many surveyors use 
in-house post processing to construct a local network and 
online services to tie the network to the geodetic system. 
The result is a tight, georeferenced control framework.

While the choice of post processing affects fieldwork during 
the control portion of a project, it also plays an important 
role in the later stages when work has shifted to kinematic 
and optical methods. One example is the occupation 
time needed for a given point. Because OPUS requires a 
minimum of two hours observation time for each point, it’s 
often faster to do shorter occupations and process them 
yourself. Commercial packages such as Trimble Business 
Center software produce excellent static results with data 
sets as short as 15 minutes. 

Filling the Gaps in RTK
Post processing also plays a role in kinematic GNSS. By 
having the ability to post process data  collected using kine-
matic methods, applications such as topographic surveys, 
as-builts and inspections can use infill methods to continue 
without interruption. 

In Denver, CH2MHill Surveyor Devin Kowbuz, P.L.S., described 
his company’s approach. “Once everything has been pro-
cessed and adjusted, we then use primarily RTK techniques,” 
he said. “But we run RTK with a PPK (post-processed kine-
matic) infill to cover loss of radio link. That way we don’t have 
gaps in data or need to go back and set additional control 
points.” Kowbuz, who uses Trimble GNSS hardware and office 
software, said that it’s very common to switch on RTK infill if 
they are in an area where communications may be unreliable. 

Knowing they can post process to get points that RTK may 
miss due to a communications issue, the crews can work 
without worrying about RTK solutions. The infill capability 
has recently moved to the real-time level with Trimble xFill 
technology, which enables survey-grade positioning to 
continue during short periods of interrupted data links.

Inside the Black Box
While RTK and GNSS surveying have seen enormous 
improvements in the past 20 years, major strides have also oc-
curred in the office. Modern GNSS processing algorithms are 
highly efficient and can produce results with ever-decreasing 
observation times. And when the new algorithms are com-
bined with advances in computing power, the results are 
impressive. A baseline that would have required two hours’ 
observation and an hour to process in the 1990s can now be 
solved with a few minutes of data and seconds of processing. 

One of the most important advances in GNSS processing 
is in the area of solving the carrier-phase integer ambiguity.  
Trimble’s HD-GNSS processing engine provides a new 
approach that takes advantage of the improved tracking 
capability of modern GNSS receivers. Rather than focusing 
on the discontinuous transition from float to fixed integer 
solutions, HD-GNSS provides a rapid, continuous conver-
gence to a precise solution. These techniques are used by 
Trimble Business Center for post processing kinematic and 
static surveys. 

With all the advances in the field, are the days of post 
processing coming to a rapid end? In a word, no. Surveyors 
clearly understand the value that post processing provides 
to them and their clients. Kowbuz sums it up: “Post pro-
cessing is an essential part of a professional skill set that 
a surveyor should provide. We have developed a system 
that works quite efficiently. We use the various equipment 
and techniques from static to post-processed kinematic to 
RTK and RTN. We employ all of it, using whatever suits our 
clients efficiently and accurately for a given day and need.”  

See feature article in POB'S March issue: www.pobonline.com

GNSS vectors and observation times are seen in a single display. Modern post-processing techniques can save time in both field and office.