Technology to collect data in terrain with GNSS
GNSS instruments and accuracy
To understand the accuracy of measurement in TopoL we have to know something
about GNSS accuracy.
First of all it depends on GNSS instrument, antenna etc. For example it is
better to use external antenna, otherwise some satellites can be hidden by
It also depends on number of sattelites and there distribution on sky. So it
is important to check the PDOP and HDOP values.
bad distribution of GNSS sattelites
good distribution of GNSS sattelites
- 1 This is the highest possible confidence level to be used for applications
demanding the highest possible precision at all times.
- 1–2 At this confidence level, positional measurements are considered
accurate enough to meet all but the most sensitive applications.
- 2–5 Represents a level that marks the minimum appropriate for making
business decisions. Positional measurements could be used to make reliable
in-route navigation suggestions to the user.
- 5–10 Positional measurements could be used for calculations, but the fix
quality could still be improved. A more open view of the sky is
- 10–20 Represents a low confidence level. Positional measurements should be
discarded or used only to indicate a very rough estimate of the current
- >20 At this level, measurements are inaccurate by as much as 300 meters
with a 6 meter accurate device (50 DOP × 6 meters) and should be
Then it is important to use proper measuring method in TopoL. The most
accurate is avaring for time interval. Longer time higher accuracy we
There are also other sattelites like GLONASS, SBAS which are used to
calculate the position.
Geographical information systems
TopoL xT is general Geographic Information
System software, which can be adjusted for applications in many areas. It allows
the creation, maintenance, analyses and presentation of geographical data.
It enables direct connection of GNSS devices.
TopoL Mobile is cheap and simple GIS
solution for field data collection and navigation with GNSS. It runs under
Windows CE, Windows Mobile operating system on Pocket PC.