TAG 
MU data | 
, Sensor 
inertial | 
| answer 
nt work | 
e mode. | 
he TAG 
volved, | 
imental | 
ie TAG 
scribe a | 
EM 
direct | 
remote 
mobile 
ition. | 
/ some 
jectory | 
ons, all | 
mplicit 
tability | 
erstood | 
tential | 
GNSS | 
em to | 
means 
and in | 
bed in 
to be 
successful so far. The system was extended to various 
instruments and applications. It was used in several distinct 
experiments and studies on the topics mentioned above. The 
actual potential of TAG will be described in the following 
sections. 
3 TAG FUNCTIONALITIES 
3.4 General Architecture 
The system is composed of a series of hardware (HW) and 
software (SW) modules (see figure 1): 
a) The Control Unit (CU). 
The CU, which is in charge of acquiring, processing and storing 
the navigation data, is based on a commercially available 
industrial computer with a Pentium 4 at 2.4 GHz CPU and 1 Gb 
of RAM inside a 4U height 19 inch rack. The CU is subdivided 
in a series of modules: 
= GCU GNSS receivers Control Unit. 
= ICU IMU control unit. 
= TSU Time Synchronization Unit. 
=  OIU Operation Interface Unit. 
= RNU Real Time Navigation Unit. 
High development efforts could be avoided by relying on a 
series of HW components based on Comercial-Off the Shelf 
(COTS) devices, which guarantee the desired functionality. 
b) The Power Unit (PU) 
The function of the PU is to supply the control unit and the 
sensors with the power they need for operation. 
The PU is subdivided into the following modules: 
=  BPU Basic Power Unit. 
=  UPU Uninterruptible Power Unit. 
c) The sensors. 
TAG is capable of capturing data from various types of external 
sensors. This includes for example GNSS antennas, inertial 
measurement units (IMU), digital cameras, odometers or digital 
compasses and barometers. It is one of the key design issues of 
TAG to be open to multiple sensor use and to extensions with 
new types of sensors. 
While the HW components basically consist of COTS devices, 
the software for TAG is the development work of the Institute 
of Geomatics. The challenge here is that the system can be 
operated in various modes and for quite distinct purposes with 
multiples sensores and sometimes in real time. Figure 2 gives 
an overview on the SW configuration. The details of the 
elements will be described further on. 
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part Bl. Istanbul 2004 
   
GCU (HW) 
(GPS RX) 
     
   
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
EXT 1— 
SENSOR 
um | TTT ETT i 
LE - Eu | | 
| PLANE Bf 
OUT El 
re BATT 
| 
i veu | 
i | 
iE OUT | 
POWER UNIT (PU) 
Fig.1- HW configuration diagram 
| IMU device | GPS device 
  
TSU ICU GCU | 
  
  
  
  
| IMU data | I^ GPs data 
| | ] 
? : 
* Y Y Y oy 
(4 { [fl 
camera tags others IMU data GUI RINEX data 
storage storage output Storage 
time * IMU data 
Fig.2 - SW configuration diagram 
3.2  GNSS/INS data capturing 
The GNSS receiver Control Unit (GCU) consists of the GNSS 
receiver and a controlling SW. 
The implemented HW device is a geodetic GPS receiver 
(Novatel Millenium OEM-3, 12 LI/L2 channels) integrated 
within the CU rack. The interface is composed of the data ports 
(RS-232) and some trigger signals. 
The GCU SW is in charge of capturing all the data generated by 
the receiver: GPS reference time, satellites phase and code 
signals and ephemeredes (RINEX) and position messages 
(NMEA). 
The function of the IMU Control Unit (ICU) is the reception of 
the data generated by the IMU through a specific interface. 
Given the large number of IMUs with different characteristics 
this unit should be adapted on the SW level to the specific 
interface of the IMU/s that is/are being used in a defined 
configuration.