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gsr ■* ' it 
the highest resolution and quality possible in order that it could 
be re-utilised and data restituted at various later stages for vari 
ous purposes, including the on-going monitoring of the sites. 
Thus the metric accuracy had to be very high as was also the 
quality of the photogrammetry and the surface detailing using 
laser scanning. 
The MCR’s 3DID team was naturally aware that before digital 
photogrammetry came into existence, surveyors had used 
theodolites to provide an accurate reference measurement lattice 
within which conventional film-based photogrammetry could be 
utilised within acceptable metric error levels. A Theodolite 
Total station registers 3 dimensional co-ordinates and is the 
only tool that offers the possibility of maintaining overall preci 
sion by using a closed-network system. This data can be read 
up to an accuracy of 0.1mm. The Theodolite Total station is not 
designed for creating virtual surfaces and contours, as are pho 
togrammetry and laser scanning. However, as the most precise 
instrument of the three mentioned, the co-ordinates gathered 
from the theodolite total station may be used to consolidate all 
the data generated by the other surveying tools The 3DID team 
therefore resolved to use a theodolite to achieve five objectives: 
a) To create a closed network providing an accurate frame 
work against which the digital photogrammetry could be 
tacked on and measured 
b) To set-up a one-stop target regime that can be utilised by 
both photogrammetry and laser scanning ; 
c) To laser scan the temple site using the same targets left in 
an identical position when previously used by the 
theodolite and the digital photogrammetry. 
d) To take the results produced independently by the digital 
photogrammetry and the laser scanning at the data acqui 
sition stage and “marry” these results into one integrated 
and composite image where the outlines are largely pro 
duced using photogrammetry and the detailed surface im 
aging is produced using laser scanning 
e) To compare the results of the stitching of the laser scans 
by the restitution software with those obtained by photo 
grammetry in order to assess the levels of accuracy ob 
tainable by the different systems independently; 
Thus the concept of Thealasermetry 3 was bom: instead of using 
two devices in synch 4 as proposed by Beraldin et. al., 3DID 
opted for 3 classes of device used in conjunction - theodolite, 
laser scanner and digital photogrammetry. The MCR team also 
opted to run a series of tests in pilot sites in order to identify 
other difficulties, strengths and weaknesses of the different 
classes of devices being employed. 
The Thealasermetry experiment was organised in the following 
stages: 
1. A sample survey at various grades of resolution of part of 
the Ggantija temples in Gozo (December 2001) was under 
taken to test the data acquisition capabilities of MCR’s 
The reasons for coining the word Theodolite in have been lost in the 
mists of time vide Alasdair Downes Q & A Theodolite 
http://www.quinion.com/words/qa/qa-thel.htm Thea (Greek for 
sight) is here being proposed together with lasermetry since all 3 
systems are line-of-sight systems and many modem Total Station 
Theodolites employ laser range-finding systems too. 
I.e. a digital camera and a 3D range camera 
SOISIC LG scanner and the restitution (including stitching) 
abilities of MENSI’s 3D IPSOS Software; 
2. A sample digital photogrammetrical survey(January 2002) 
was carried out on the same part of the Ggantija temples 
which had also been subject to a laser scan, thus providing 
the basic data which would enable a test marriage between 
the laser scan data and the photogrammetric data; 
3. A sample laser scan at high resolution was carried out on 
the Tarxien Temple altar at the National Musuem of Ar 
chaeology in Malta (December 2001) in order to measure 
the MENSI LG SOISIC scanner’s accuracy on an object 
which is roughly the same size as that use for the Beraldin 
case study; 
4. A sample laser scan at various grades of resolution was 
carried out on a non-megalithic monument (the crypt of St. 
John’s Co-Cathedral in Malta) in order to evaluate other 
system limitations that may be learned from different type 
of architectural/archaeological applications; 
5. A sample laser scan at various grades of resolution was 
carried out at the San Salvatore Church in Kalkara (January 
2002) in order to test operational advantages between the 
MENSI LG SOISIC (plane triangulation) laser scanner and 
the MENSI NG 100 time-of-flight laser scanner in prepara 
tion for the Temples Survey Project; 
6. A small-scale integration test was undertaken (March 2002) 
combining photogrammetric data and laser scan data ob 
tained from Ggantija, using the vector outlines obtained 
from photgrammetry and the data from laser scanning to 
provide the in-fill between the outlines; 
7. A sample combined survey was carried out at a portion of 
Tarxien Temples in Malta (June 2002) using the following 
systems in combination: 
a. Spheres with an integrated prism capable of being used 
as a target by both the theodolite and the laser scanner 
in quick succession without their being moved in the 
process; 
b. Theodolite Total Station to provide framework within 
which to integrate data from digital photogrammetry 
and laser scanner; 
c. SOISIC LG Laser scanner to work in areas with range 
2m-5m; 
d. SOISIC NG Laser scanner to carry out fast scans to 
compare results with those obtained from SOISIC LG; 
e. Nikon D1 digital camera to provide digital photogram 
metry data for back-office integration and restitution 
process; 
8. A large scale integration test of the data captured during 
stage 7 was carried out (June 2002) using DIAP and 3D Ip- 
sos software in order to repeat the successful integration 
test carried out at stage 6 but this time on a larger scale and 
with a clear view to minimising metric propagation error 
having used the Thealasermetry process Stages 1 to 6 have 
been successfully completed and will be fully reported upon 
in this paper while parts of stages 7 & 8 were still work-in 
progress at the time of going to press but will be completed 
- and reported upon by the time the paper is due to be pre 
sented at the September 2002 Corfu workshop.