TIGHT INTEGRATION OF GNSS POST-PROCESSED VIRTUAL REFERENCE 
STATION WITH INERTIAL DATA FOR INCREASED ACCURACY AND 
PRODUCTIVITY OF AIRBORNE MAPPING 
J. Hutton 3 *, Alan Ip a , T. Bourke 3 , B. Scherzinger 3 , N. Gopaul 3 , P. Canter 3 , 
I. Oveland b , L. Blankenberg b 
3 Applanix Corporation, 85 Leek Cr., Richmond Hill, Ontario, Canada L4B 3B3 
(jhutton, aip, tbourke, bscherzinger, ngopaul, pcanter)@applanix.com 
b BLOM Geomatics AS, Drammensveien, 165 N-0277 Oslo, Norway 
(leb@blomgeomatics.no) 
ICWG V/l 
KEY WORDS: Aerial Survey, GNSS/INS Integration, IMU, Direct Georeferencing, Photogrammetry 
ABSTRACT: 
GNSS-Aided Inertial Navigation for Direct Georeferencing of aerial imagery and other sensors such as LIDAR is a well accepted 
technology that has been in use since the mid 1990’s. Position accuracies of 10 cm RMS horizontal and 15 cm RMS vertical are 
routinely achieved using post-processed kinematic ambiguity resolution (KAR) differential GNSS processing along with specific 
operational restrictions that are necessary due to the nature of the airborne environment. These include: flying turns of less than 20 
deg bank angle, flying less than 30 km from a reference GNSS receiver in order to correctly fix integer ambiguities, and keeping the 
maximum baseline separation to less than 75 km once the ambiguities are fixed. Each of these restrictions significantly reduces the 
efficiency of airborne mapping, and hence increases the overall cost. In order to overcome these limitations, Applanix has developed 
a new patent pending post-processed GNSS-Aided INS software called POSPac Mobile Mapping Suite (formerly POSPac Air 5.0). 
This software incorporates two new technologies, Applanix IN-Fusion™ and Applanix SmartBase™, that together provide the 
ability to fly turns with greater than 20 deg bank angle, and fly at distances up to 70 km from the nearest GNSS reference station, 
without sacrificing accuracy or reliability. This paper provides details on the new Applanix IN-Fusion technology and Applanix 
SmartBase module implemented in POSPac MMS. It will then present results from a series of studies into the performance of 
POSPac MMS using various reference station networks from around the world. Finally it will present performance and cost saving 
results when flying bank angles at greater than 20 degs from a series of actual survey flights. 
1. INTRODUCTION 
1.1 Applanix IN-Fusion Technology 
High accuracy carrier phase differential GNSS processing 
involves searching for the correct number of integer cycles of 
the LI carrier signal between the rover antenna and each 
satellite. Since the correct number of integer cycles is originally 
unknown, they are referred to as the cycle ambiguities. 
Estimation of the ambiguities requires a continual lock on the 
signal to each satellite in order for the solution to remain 
converged. If the aircraft turns with a bank angle greater than 
15 to 20 deg, the wing can block the view of the satellites from 
the GNSS antenna, causing the solution to reset and begin 
another search. Flat turns increase the time required to fly the 
survey, and are problematic in restricted flight zones where 
there may not be enough room to safely manoeuvre. They also 
increase the stress level on the crew, which leads to fatigue and 
potential operational errors. 
These problems are solved via the Applanix IN-Fusion™ 
technology, which implements an Inertially-Aided Kinematic 
Ambiguity Resolution (IAKAR) algorithm to compute the 
GNSS ambiguities. In this approach the inertial data and raw 
allows the inertial data to be used to solve for the integer 
ambiguities. The IAKAR architecture is illustrated Figure 1. 
Figure 1. Applanix IN-Fusion IAKAR Architecture 
GNSS observables (phase and range measurements) are 
processed in a single tightly integrated Kalman filter, which 
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With IAKAR, if there is a cycle slip or outage in the GNSS data, 
the inertial data keeps a “memory” of the ambiguity, allowing 
the correct integer ambiguity to be quickly re-established