OEEPE TEST ON ORTHOPHOTO AND STEREO-ORTHOPHOTO ACCURACY
OEEPE Guy DUCHER
ORGANISATION EUROPEENNE D'ETUDES
PHOTOGRAMMETRIQUES EXPERIMENTALES IGN (F) FRANCE Comm. IV,
ABSTRACT
A test has been conducted by OEEPE which aimed at obtaining
information onthe impact of five main parameters on the metrical
accuracy of typical orthophotos and stereo-orthophotographs.
These parameters consist of the scale of the aerial survey to
rectify, that of the survey from which the D.T.M is derived,
that of the orthophoto, the slit width and the scanning direction.
Three scales were considered for aerial surveys and D.T.Ms(1:60 K.
1:30 K and 1:16 K-scale) and two for output products (1:25 K and
1:5 K-scale).
RESUME
L'OFEPE a effectué un essai visant à étudier l'influence de cinq
facteurs essentiels sur la précision métrique des orthophotos et
stéréo- orthophotographies.
Il s'agit de l'échelle du levé aérien à orthophotographier, de
celle du levé dont on a tiré le M.N.T, de l'échelle de l'orthophoto
de la longueur de la fente et du sens de balayage.
On a pris en compte trois échelles pour les levés aériens et les
M.N.T (1 : 60 K et 1 : 30K et.1 : 16 K) et deux échelles pour les
produits en sortie (1 : 25 K et 1 : 5 K).
Key Words — : Accuracy Altimetry DEM Mapping Orthophoto Stereoscopic 3-D
PROJECT DESCRIPTION
TEST AREA
The test area is located in France, in the Massif Central area,
around the small town of Lacapelle Marival (Lot "département")
consisting of 1200 people.
It has a wide range of relief from 350 m up to 628 m above
datum, including valleys as deep as 150 m near its sides and
slopes ranging from moderate (some 30 Z slopes in the middle)
to steep (many 50 % to 60 Z slopes on the hillsides).
The terrain is gently rolling in the middle of the area.
Due to the neighbourhood of the "Causse de Gramat" the forest
is not very thick, while many natural features are dissemina-
ted over the entire test area, which is portrayed on the basic
map at 1 : 25 K-scale with a 10 m contour interval.
The test area covered a full frame at 1:30 K-scale and had a
wide range of relief and slopes. It was fitted with as many as
271 fixed points, including 170 natural features and 101 signali-
sed points, suited to 1:16 K and 1:30 K-scale surveys.
The accuracy of these points can be inferred from the origin
of their determination and from some redundancy in their
measurements. Their accuracy is ranging from about 20 cm to 40 cm.
Considering the present trend in the national mapping agencies
to establish heighting databases at medium scale by digitising
contours of base map series at 1 : 25 K-scale or by stereo-
plotting pairs at 1 : 30 K-scale and storing the related data
in a vector format, it was decided to deliver to each producing
center the required altimetric data in a format consisting of
contours stored on magnetic tape directly.
Each operative center was responsible for computing the pro-
files required for rectifying aerial photographs into the ortho
and stereo-orthophotos it has agreed to do, using its own al-
gorithms to interpolate the relevant data from the contours.
PRODUCTS The test was conducted by IGN (F) acting as pilot center
(but also as operative and assessing center). Seven
producing centers delivered a total number of 90 products,out of
which 59 were assessed, analyzed and retained for their results,
comprising 29 orthophotos and 30 stereomates.
600
