Full text: Remote sensing for resources development and environmental management (Volume 1)

lines (cut through the jungle after the photos are 
flown), can be exactly reconstructed. 
Considering the quality of the provided airphotos 
in terms of variations in scale and tilt, the 
slotted templet method was in this case found to 
yield unsatisfactory results, even though the 
assembly of templets was fitted to pass-points 
identified and linked to traverses by 
Euroconsult's topographical team. Although the 
location and orientation of each individual 
airphoto was in theory in this way fixed relative 
to the planimetrie map of traverses, in actual 
fact it appeared that locations of field 
observations could not always be traced back. This 
was especially valid for parts of the terrain 
remote from pass-points. 
2.2 Use of Landsat 
Since the Australian Landsat Station (ALS) went on 
stream early in 1981, ample coverage by Landsat 
MSS imagery of southern Irian Jaya has become 
available. Although Landsat has been around since 
1972, up to the establishment of ALS only a 
one-time acquisition of the region existed and 
then mostly covered with clouds. In recent years, 
however, consultants operating in the area have 
had at their disposal more and more cloud-free 
Landsat MSS imagery to complement and connect the 
existing scattered blocks of aerial photography. 
As will be shown below, with this development 
the most important mapping constraint mentioned 
above was overcome by Euroconsult. Landsat MSS 
bulk processed photographic products appeared 
sufficiently true to scale and shape as to serve 
as planimetric control for the construction of 
airphoto-derived basemaps. 
3.1 Principles 
The method is based on the assumption that 
directions to objects, when reckoned from the 
centre of a vertical aerial photograph, are 
constant under all conditions of elevation 
difference and scale change. Under this principle 
a scale adjustment can be made for a block of 
photographs by allowing corresponding points on 
adjacent airphotos freedom of movement away from 
and towards their centre points. The block of 
airphotos can thus be adjusted to scale, by making 
it fit a number of control points (Slama et al, 
The slotted templet method is a mechanical 
solution based on this principle. Although this 
method is obsolete as regards modern 
photogrammetric triangulation, in practice the 
slotted templet method is often still used in the 
field as the best option open to achieve a more or 
less usable result (depending on the quality of 
the photography). 
3.2 Conditions for use 
A prerequisite for the proper working of slotted 
templet method is that the centres (principal 
points.) should more or less coincide with the 
nadir points of the airphotos. Another condition 
is that the individual scales of the photos should 
not fluctuate too much. In other words, the aerial 
photographs should be flown carefully, with 
minimum tilt and altitude variations. 
Unfortunately, this is not always the case with 
aerial photography made available to consultants 
working in developing countries. In addition to 
the fact that tilt and scale variations hamper the 
use of the slotted templet method, the method also 
requires a tremendous amount of time and patience 
to physically assemble the entire set of templets. 
4.1 Principle 
The principle on which the Landsat airphoto map 
control method is based, is the merging of 
Landsat's high planimetric accuracy over large 
areas, with the high local detail of aerial 
Ideally, merging of these two characteristics is 
best done by registration of the airphoto onto the 
Landsat scene with a rectifier. Next, the settings 
which compensate tilt and scale are freezed. 
Finally, the airphoto is blown-up to basemap 
scale. Though airphoto and Landsat can be matched 
optimally in this way, the procedure clearly is 
not suited for application under field conditions. 
As a result, we have resorted to an approach in 
which corresponding control points are sought on 
Landsat scene and airphotos. This basically 
approximates the above procedure. It is this 
technique that is described in the next Section. 
4.2 Description 
The following is a step-by-step guide on how to 
use Landsat in combination with airphotos to 
produce a basemap under field conditions. 
* A Landsat scene covering the area of study is 
ordered in a conveniently large scale. (At ALS, 
1/I6th of an MSS scene can be ordered at a scale 
of 1/50 000 in false-colour, with excellent 
results.) The date of aquisition should be close 
to that of the aerial photography to facilitate 
the next step. 
* Salient landmarks discernible on both airphoto 
and Landsat are pinpointed and allocated a number. 
* Temporary and arbitrary x-y coordinates of the 
points, scaled off the Landsat scene with the aid 
of translucent millimetre grid on a stable base, 
are multiplied by the scale ratio factor so that 
the points can be plotted on the basemap scale 
(nominal photo scale). The resulting matrix of 
points serves as a field of control points for the 
assembly of the air photographs in a map. 
* A minimum of three control points per airphoto 
is required in order to correct not only scale but 
also tilt variations. More than three control 
points enable a better check on compatibility 
between Landsat and corresponding airphoto points 
and increase the matching accuracy between Landsat 
and airphoto. 
* In actual practice an optical pantograph can 
best be used to mate the control points on the 
airphotos with their corresponding points on the 
basemap. Pantographs that allow the introduction of 
a certain amount of distortion are to be preferred 
(e.g. the Stereo Facet Plotter by O.M.I.) as they 
make it possible to approximately adjust for 
* Using this instrument the principal points of 
the photographs can be transferred to the basemap, 
including all relevant geographic information 
visible on the aerial photographs. 
The resulting map contains pertinent, highly 
detailed, geographic information true to scale and

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