49 
me and patience 
set of templets. 
ROL METHOD 
airphoto map 
rging of 
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of aerial 
aracteristics is 
irphoto onto the 
xt, the settings 
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re clearly is 
ield conditions, 
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It is this 
next Section. 
ide on how to 
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scale. (At ALS, 
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both airphoto 
llocated a number. 
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o factor so that 
basemap scale 
ting matrix of 
rol points for the 
in a map. 
ts per airphoto 
not only scale but 
three control 
compatibility 
g airphoto points 
cy between Landsat 
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points on the 
ng points on the 
the introduction of 
re to be preferred 
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y adjust for 
pal points of 
ed to the basemap, 
c information 
s. 
at, highly 
rue to scale and 
orientation. The question now is how true this map 
really is. In the following Section the 
theoretical and empirical accuracy of map control 
by Landsat is discussed. 
4.3 Theoretical accuracy 
ALS Landsat bulk processed photographic products 
are not portrayed with a particular map projection 
in mind. Apart from corrections for systematic 
influences (e.g. mirror velocity) ALS also corrects 
its images for panoramic distortion and earth 
curvature (Dovey, 1986). Whatever the along-line 
correction procedure may be, the portrayal result 
can only be related to an oblique cylindrical 
projection with as reference line the ground track 
of the satellite. Since the maximum distance away 
from this line in an MSS scene is only some ninety 
km, the theoretical distortion cannot amount to 
very much. As a result, ALS's bulk processed 
imagery indeed provides high planimetric accuracy 
over large areas as will be shown in Section 4.4. 
However, in bulk processing no account is taken 
of the direction in which Landsat is pointing 
during image acquisition. It is simply assumed 
that the satellite is pointing straight down, and 
scanning at right angles to its own path. To 
obtain higher accuracy than in bulk processed 
imagery it is necessary to employ ground control 
points with precisely known latitudes and longitudes. 
This permits a yaw-pitch-roll correction to be 
applied so that Landsat scenes can be produced 
with a higher planimetric accuracy (Dovey, 1983). 
Unfortunately, however, no precision products can 
be expected for the remote areas under discussion 
here, since in these areas points with known 
latitude/longitude are hard to come by. 
Another activity which influences accuracy is 
the pinpointing of the photo points in the 
Landsat image. The precision with which this can 
be done is not limited to pixel size as the points 
can be located to within pixel boundaries by 
interpolation if the airphoto is used as guidance. 
An MSS blow-up to e.g. 1/50 000 scale, of course, 
does nothing to increase Landsat's inherent accuracy 
but it does increase the accuracy of the cartographer 
who has to locate those points within the pixels. 
It should be remarked here that Landsat's spatial 
resolution, contrary to popular opinion, is not so 
much a function of the pixel size, but rather an 
expression of the variation in the spatial 
information content overlain and 'blurred' by the 
pixel grid. Thus defined, Landsat's spatial 
resolution is much finer than would be suggested 
by its pixel dimensions. 
Though it is unfeasible to quantify the method's 
accuracy on the basis of the above information, it 
has been possible, during the last few years in 
Irian Jaya, to assess its degree of magnitude 
thanks to 1 m accuracy measurements by the 
topographical teams. 
4.4 Empirical accuracy 
In Irian Jaya Euroconsult was in a position to 
test a number of times the accuracy of the method 
under true field conditions. For six different 
areas ranging in size between 40 000 and 80 000 ha 
basemaps depicting the drainage network were 
produced using the Landsat map control method. The 
team also prepared a planimetric map in UTM projection 
for each area, showing traverses and secondary 
levelling lines (parallel to each other with 1 km 
spacing), along which all encountered river and 
stream intersections were indicated. The Landsat 
controlled basemap and the UTM planimetric map, 
both at the same scale, could now be matched by 
fitting river crossing to the drainage lines. 
As in this case the drainage pattern is a random 
one, it follows that the intersection pattern with 
parallel lines, is also random. It is remarkable 
that this random field of intersection points fits 
with the drainage pattern of the basemap as well 
as it does. The few mismatches invariably proved 
to be caused by mislocations of small streams on 
the air photographs. The method of best possible 
fit, used to mate intersections with streams, 
showed that the mean deviation which occurred was 
around 1.5 mm (when compensated for perpendicular 
intersection) in random direction, at a scale of 
1/20 000. 
As ALS uses a process of portrayal which cannot 
be defined by a particular set of mathematical 
formulae, but which resembles the method as 
mathematically described for an oblique Mercator 
projection, and as the topographical team's results 
are displayed with the assistance of the UTM 
projection, a slight systematic mismatch caused by 
this difference of portrayal is to be expected. 
However, the absence of visible signs of systematic 
variation proves that for our practical purposes 
this mismatch is insignificant relative to the 
position variation caused by Landsat's geometric 
inaccuracies and with the uncertainties in the 
positioning of the control points in the Landsat 
image. 
Two other facts become apparent: 
* Without topographical work as a back-up, the 
method is adequate for the production of 
geographic maps with an accuracy requirement of 
30 m, and 
* the photo interpreter can always, irrespective 
of tilt and scale variations, reconstruct the 
location of his field data on the airphoto, thus 
optimizing the quality of the interpretation. 
5 DISCUSSION 
5.1 Comparison 
It is possible to express the mean error as a 
function of control density in a slotted templet 
block. Conversely, knowing the mean deviation (1.5 
mm at photo scale) in the airphoto map control 
method with Landsat, it is also possible to deduce 
the control density that would have been necessary 
had the slotted templet method been used. Of 
course, this comparison is only valid if photo 
tilts and scale variation are within ordinary 
limits, which as we know is not the case. 
Trorey (1947) has proved that the relationship 
is based on the theory of errors, from which it 
follows that the mean variation of image point 
locations is inversely related to the square root 
of the number of control points to which the 
slotted templet block is laid. Or 
e = kit/c)^ 
where e is the mean variation in mm, k a constant, 
t the number of templets, and c the number of 
control points. From empirical data Trorey determined 
the value of the constant k as 0.16. 
The theoretic control density (t/c) can now be 
calculated since e=1.5 and k=0.l6. It would seem 
that the 1.5 mm mean variation is comparable with 
the theoretical accuracy which would have been 
achieved with a control density of about 85 templets 
per ground control point had the slotted templet 
been used, and had airphotos been used with scale 
and tilt within acceptable limits. 
To achieve a result comparable to that of the 
Landsat airphoto map control method when using a 
set of photographs like those made available in 
southern Irian Jaya, the slotted templet method