Geography Reference
In-Depth Information
particular use of AR technologies strongly depends on the actual use case and
application domain for which AR is being used. There are a number of different
kinds of AR. Most taxonomies (Chimienti et al.
2010
) provide 4 broad classes:
marker-based AR, location-based AR, natural feature tracking and target-based
AR. We will describe various AR types later in this section. This study is focused
on the location of the user and therefore uses location-based AR.
3.3 Types of AR
3.3.1 Texture Tracking
This technique is based on extracting a number of key elements of the image, and
using those image features to track the position and orientation of the device.
A number of algorithms have been developed, among others the use of scale-
invariant feature transform (SIFT) filters providing the best results (Ruf et al.
2010
). Texture tracking is often referred as 2D tracking, as it does not use the
calculations of depth, but relies exclusively on the flat image features.
3.3.2 3D Feature Tracking
This is a more advanced technique that utilises both, 2D feature tracking as well as
depth and 3D object estimations. This technique is more accurate, but at the same
time more computationally intensive. There are good applications of this tech-
nique, and the reader can find details for example in (Vacchetti et al.
2004
).
3.3.3 Sensor Based Tracking (Location Based)
Another mechanism for real object tracking is sensor-based tracking. Sensor
tracking or location based tracking uses the fusion of several sensors to figure out
the location and orientation of the mobile device. This type of augmentation is
well suited for place/location systems, and is common on mobile phones.
Smartphones usually have a GPS, accelerometer and/or gyroscope and magnetic
field sensors built-in. This is an advantage of modern smartphones—no extra
dongles are needed.
The GPS supplies the phone with its current location, the Gyroscope or
Accelerometer in combination with the Magnetic Field sensor allows the calcu-
lation of the orientation of the phone. Together, location and orientation make
location based AR possible.
This use of GPS positioning and geographical information in context (e.g.
Google Maps data) is an example of a Location Based Service (LBS). For an
overview of LBS please refer to Raper et al. (
2007
).
