Ubiquitous User Localization for Pervasive Context-Aware Construction Applications - Mobile and Pervasive Computing in Construction - page 105

Figure 6.16 Indoor GPS tracking system
the two dimensional space and intersect in the desired position. Therefore, given
the angular information from at least two transmitters, and provided with the
position and orientation of each transmitter, a unique 3D position within the
measurement volume can be calculated. The indoor GPS eliminates the recurring
problem of accidentally interrupting a laser beam during measurement that
requires the operator to begin the measurement again.
Similarly to the previous tracking applications, the user's position and orien-
tation were continuously obtained from two different sources, in this case the
Indoor GPS and magnetic tracker. TCP sockets were used to connect directly to the
Indoor GPS system application and provide a quick and effective way for accessing
location information from a local computer/laptop. This was achieved by opening a
socket connection given the IP address and the port number, reading values in byte
string format, performing a byte manipulation on those values and extracting the x,
y, and z coordinates (Figure 6.18).
The positioning values were then used together with orientation values received
from the magnetic tracker and both were integrated in one application to retrieve
tracking information (Figure 6.19).
Figure 6.17 Triangulation approach