CIP A 2003 XIX th International Symposium, 30 September - 04 October, 2003, Antalya, Turkey
720
2. LOCAL REFERENCE SYSTEM
2.1 General Strategy
According to the agreed standards of the geodetic community
surveyors do their best to bring all measurements of a project
into a common geodetic reference frame. The normal way to
achieve this is to connect the results of the local survey to the
official state system. This, however, was not possible in our
project due to the fact that no official co-ordinates of any points
in the project area have been available until today. That is why
is was decided to define one physically identified point, which
is known to be part of the official Turkish reference system
(point no. 1000, see Figure 2) to be the fundamental point of a
local reference system.
Figure 2. Points of local reference network
To avoid negative co-ordinates in the project area this point was
given local co-ordinate values in East direction E = 10000,000
m and in North direction N = 10000,000 m in the same way. A
Turkish 1/5000 scale map was available on which the
fundamental point was identified. To make the new local
system fit as well as possible to the height system of that map,
the fundamental point was given the rounded up height value H
= 1130,000 m above sea level which was very close to the
annotated point height value of 1129,987 m in the map. By that
way of establishing the reference system it was made sure that
the height system fits with the official system and that no
confusion between the currently used local co-ordinate values
for Eastings and Northings and any other co-ordinate system
which will eventually be used in future can occur.
2.2 GPS Measurements
A set of points was established to serve as the geospatial base
for all subsequent measurements. The co-ordinates of these
points were determined by GPS baseline measurements with
two Trimble 4700 system receivers in static mode and by
calculation of co-ordinate values in postprocessing mode. The
results of the baseline measurements were processed with
Terrasat’s software package GeoGenius® which delivered a set
of geocentric co-ordinates in the WGS 84 reference frame and,
on the basis of the Earth Model JGM3/OSU91, which is a
composite of the JGM3 and OSU91A models (Merry, 2003) a
set of geographic co-ordinates and orthometric heights for all
measured points. Table 1 shows the list of plane and height co
ordinates after shifting it to the predefined co-ordinates of point
no 1000. As can be seen, the standard deviation (sE, sN, sH) of
the point co-ordinates resulting from a free network adjustment
are all in the 1 centimetre range thus establishing a highly
accurate base reference frame. This set of co-ordinates serves as
the georeferential base for all subsequent work.
Pt. No.
Easting
Northing
Height
sE
sN
sH
1000
10000,000
10000,000
1130,00
0,0
0,0
0,0
2000
9853,615
9570,622
1092,82
3,2
2,8
7,8
3000
9768,449
9419,180
1080,17
3,2
2,8
8,1
4000
8790,385
8922,818
1108,18
2,8
3,1
7,2
6000
9292,813
10415,763
1221,69
2,5
1,9
4,9
7000
9441,799
11058,075
1278,81
2,1
1,7
4,5
8000
10296,378
10332,056
1096,51
1,9
1,7
4,6
9000
10272,821
9833,549
1095,35
1,5
1,2
3,1
10000
9723,471
10454,293
1162,28
2,2
2,3
4,7
11000
11221,836
9928,892
1046,45
6,9
5,3
14,3
12000
9480,751
10308,714
1193,73
2,0
1,5
3,4
13000
10153,024
10080,383
1104,21
1,6
1,2
_A2
Table 1: Reference point co-ordinates with their relative
standard deviation values (all metric values given in unit metre)
Above that, the geographical co-ordinates as obtained from the
GPS measurements established an absolute geodetic reference
frame within the accuracy which can be obtained from absolute
GPS measurements.
2.3 Quality Checks
The quality of the local area network was checked in several
ways. Firstly, the height of the local fundamental point no. 1000
which was obtained from the world wide Earth model
JGM3/OSU91 was compared with the height which was taken
from the map. The difference was in the 4 metre range, which
seems to be within a reasonable scale. Secondly, a set of
distances was measured by electronic distance measurements
between some of the reference points. The comparison of the
independently measured distances and the distances as
calculated from co-ordinates showed that the difference in all
cases was below 2 centimetres (see Haas, 2002).
3. LARGE SCALE MAPS
In-depth archaeological field work often needs detailed large
scale maps for the georeferenced documentation of findings,
etc. In several campaigns parts of the landscape of the research
area were captured by extensive tacheometric surveys. A
sample of highly detailed 1/500 scale maps was generated (see
Figure 4) within a predefined map sheet framework (Figure 3).
