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 the body.
It also depends on number of sattelites and there distribution on sky. So it is important to check the PDOP and HDOP values.
DOP Value
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 recommended.
- 10–20 Represents a low confidence level. Positional measurements should be discarded or used only to indicate a very rough estimate of the current location.
- >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 discarded.
Then it is important to use proper measuring method in TopoL. The most accurate is avaring for time interval. Longer time higher accuracy we have got.
There are also other sattelites like GLONASS, SBAS which are used to calculate the position.
Geographical information systems TopoL
TopoL xT
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
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.