A preliminary step is a classical aerial triangulation computa-
tion controlled on known ground points. The results are checked
on other known ground points (check points) in order to appre-
ciate the quality of the photogrammetric reference whichis dif-
ferent on the three sites.
A first strip consists of comparing GPS coordinates transformed
in Lambert projection (Clarke 1880 ellipsoïd) with results of
the previous aerial triangulation calculation.’ This Comparison
gives for each strip :
-on one hand, a translation bias, function of- differernt'para-
meters in relation with GPS system or on-board equipment (ex-
posure delay - distance between antenna and camera)
- on the other hand a standard deviation which characterizes
the accuracy relative to photogrammetric reference. :
The following steps comprise introduction.of GPS data in aerial
triangulation when considering several hypothesis for this cal-
culation:
- use of" all control- points
- Use ot only four control points at the angles.of the block
- elimination of North-South strips, in order to appreciate
their importance
- elimination of all ‘control points and introduétion of;an“‘ina-
ginary point at the center of the block, what allow to simu-
late GPS on-site measurements.
V) Results
A) Amiens test site
On this site there was an old enough aerial triangulation net-
work, established for a mission at a scale of 1/6000. The
ageing of natural control points and transfer of these points
on the 1986 photographs imply a medium accuracy of the photo-
grammetric reference as shown by residuals of aerotriangulation
On-control points:
Flight of June 18 (Amiens - I)
Ex = 0,21 m }
£y 2 0,24 m ) £m » 0,27 m
£2 127033 wm )
Flight of June 19 (Amiens - II)
Ex -0,29m)
yg 19,39 m ) €m - 0,34 m
&7 20,36 m ))
For. the following results, we consider only^Amiens-I flight':
a) Comparison between coordinates of the points of view and
GPS measurements
Strip-l
Tx m 0,5l.m N^ X. zm0,34. m
Ty Sad, 22-N Ty. = 0,26 m
TZ. = 3,55: m S em 0 9.1
