lapping 
(EEC) 
cale of 
dering 
oposal, 
ing the 
| in 77 
iditions 
ntract. 
sed the 
during 
it was 
Leica 
station, 
raphy) 
ers. for 
These 
maps, 
’ouncil 
ve and 
1996, 
- This 
40,000 
et and 
rolling 
ng the 
vas an 
|^ and 
nerale 
ted to 
merit, 
| their 
lihood 
Over 
nd led 
ild be 
5). A 
nplete 
imistic 
r this 
  
  
2. THE PHOTOGRAMMETRIC FLIGHT 
2.1 The Planning 
The entire flight project was executed by means of the "Flight- 
Planning" program (an Ascot routine see below) which 
identified the geographic coordinates in space within the Irish 
reference system ellipsoid of all the projection centers of the 
expected 4000 photographs. The data, stored on PCMCIA 
cards, permitted the automatic operation of the RC 30 camera 
driven by a PC connected to a Magnavox GPS receiver. CGR 
technicians used this planning methodology for the first time. 
The main difficulty experienced was the difficulty of 
minimizing the number of strips because the program assumes 
a flat ground and does not allow forvariations in ground relief; 
moreover, the transformation between geodetic datum (i.e. 
Irish Grid and WGS84) is performed by simple translations 
only, sufficient for a flying height of 6000 m, but probably 
inadequate for a low level flying heights. An illustration of the 
flight plan of the aerial photographic survey is shown in fig. 1. 
  
  
  
  
  
Figure 1 - Flight plan of the aerial photographic survey of 
Ireland 
2.2 The flight 
The execution of the survey was based on sun's rays 
inclinations as given in tables. Accordingly, hours of 
operation for the sun's inclinations of at least 30? are at a 
maximum in July, from 08.50 to 18.05 and an operational 
minimum in October from 11.55 to 14.30. As a result of 
unprecedented good weather during the summer of 1995 the 
aerial photography was successfully completed in 12 working 
days. Because of the availability of the Lear Jet and the 
exceptionally favourable meteorological conditions it was 
possible to fly for seven hours per day while remaining within 
the specifications of the contract. 4164 photos were taken in 
77 strips running east and west across Ireland covering 70,025 
square kilometres of land at a scale of about 1:40,000 with 
60% end lap and 25% side lap. The survey was executed with 
the Lear Jet 25CI-BMFE (see figure 2) flying at an average 
height of 21,000 ft at a speed of 350 kts and utilising a Wild 
RC 30 FMC 15/4 camera with a calibrated lens of 152.93 mm 
and Kodak 2412 Aerografic Panatomic X film. The automatic 
functioning of the camera by GPS has taken up about 90% of 
the entire work. During the flight the pilot has used the GPS 
system as an assisted navigational instrument. The aircraft was 
based at in Shannon (in the south) and Baldonnel (near 
Dublin) airports to minimize transfer times to the area 
requiring photography. The total number of operative flights 
were 18 out of a total of about 50 flight hours. 
  
Figure 2 - The Lear Jet 25CI-BMFE used for the work. 
2.3 Photos development 
The film was developed, checked, and titled at the offices of 
the CGR in Parma, Italy. There was no need to repeat some of 
the photographs because of non alignment of the principal 
points (175°-180°), lack of parallelism between strips, failed 
coverage of coastal areas, cloud coverage of more than 5% in 
the area and 10% within a single photo, drift more than 5% 
and camera tilt more than 2°, exceeding average density of 
the negatives from 0.80 to 1.10 with variations from 0.20 to 
1.50. The aerial photos were free of gaps shadows and clouds. 
A photo of an assembled mosaic of the aerial photo coverage 
of Ireland is given in figure 3. 
3. GPS FOR AERIAL TRIANGULATION 
In the last few years the use of the GPS system in aerial 
photogrammetry has increased both for navigation purposes 
and for aerial triangulation. In 1995 the satellite constellation 
has been concluded both for the minimum number of available 
satellites and for the daily windows of visibility. Thanks to the 
research experiences over the last few years with (Astori et al. 
1992, Forlani et al. 1994) it was possible to face with 
competence the enourmous positioning task of such a project 
covering the survey of a whole country. 
The tender signed between the Compagnia Generale 
Ripreseaeree (CGR) and the Ordnance Survey wanted 
together with the photos, photographic projection center 
coordinates with an accuracy of + 1m. For this purpose, the 
CGR bought the whole Ascot Leica hardware and software 
package and the GPS receiver hardware for both the aerial 
155 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B1. Vienna 1996