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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B2. Istanbul 2004
Fig. 4 — Public area in the archaeological sites of Morgantina
and Solunto.
Initially a static survey has been performed with dual frequency
receivers and differential post processing error correction,
choosing some clearly visible points, both on the maps and
orthophotos at a scale of 1:10000.
Five points (distributed in the area at regular distance) has been
surveyed stopping on every points for 30 minutes.
The survey has been carried out with 3 dual frequency receivers
(Topcon mod. Legacy-E-GGD), one of which positioned over a
point of known coordinates and the others over the surveyed
points of the archaeological site.
So it was possible to obtain both the relative position and the
absolute position of surveyed points, in UTM-WGSS84 system.
In order to test the two pocket GPS receivers, the survey,
carried out by these ones, has been exported in shape format
and superimposed to georeferenced map.
The two pocket GPSs used in this experimentation are:
- a Magellan Sportrack Map;
- aBluetooth EMTAC GPS with Sirf II LP chip
E
01234 Meters
Fig. 5 — Positional variation relating to a fixed point
The following considerations come out from this comparison:
l. the starting time of EGNOS differential correction is
about of 10-15 minutes;
2. usually only signal from the IOR Egnos satellite is
always received; signal from AOR satellite is not
constant;
3. the GPS receivers show good positioning accuracy
going along a straight path;
4. when the surveyor stands on a point, the received
position varies within a circle of 2.5 meters, but the
first position, received when the surveyor stops,
seems to be the best (Fig. 5);
=
5. tracks saved in the memory of the receivers are
characterized by a positioning accuracy varying from
| m and 3.5 m with a similar precision.
Generally, this kind of accuracy makes these instruments
suitable for fruition of an archaeological area of this typology,
but the pocket GPSs tested show a different behaviour probably
due to different GPS chips used (Fig. 6).
Paths
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Fig. 6 — Comparison of paths surveyed with the two pocket
GPS receivers used for the experimentation
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Error absolute frequency
Biuetooth Pocket GPS
Error absolute frequency
Magellan Sport Track Map GPS
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Fig. 7 — Absolute error frequency along the path
With reference to figures, it is possible to say that the Bluetooth
EMTAC GPS with SirF Star II LP performs better than
Magellan Sport Track Map (Fig. 7); actually the EMTAC is the
most suitable instruments for the aims proposed. the Bluetooth
EMTAC GPS performs well also in complex paths as that of
Fig. 8.
But obviously, it is necessary to produce extensive tests to find
all pocket GPS suitable for this kind of use.
