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PHOTOGRAMMETRIC ENGINEERING 
stances (climatical or soil conditions), or can 
be caused by human interference (traces of 
shifting cultivation, logging, grass fires, etc.). 
The identification of types is mostly based 
upon the following principles: 
1) General aspect of the vegetational cover 
to be differentiated in closed forest, open 
forest, woodland forest, bushes, scrub 
and grass land. Further also vegetation 
types caused by shifting cultivation, as 
occupied agricultural fields, old and 
young secondary forest. 
2) Possible subdifferentiations based upon 
particular aspects of the crown canopy 
caused by local differences in tone and 
texture of the individual trees. The 
identification of the individual tree spe- 
cies in the tropical forests is generally 
impossible on the photographs caused 
by the very heterogeneous species com- 
position of these forests. However, the 
typical distinctive pattern based upon a 
combination of features brought out in 
stereo of tree height, crown size and ap- 
pearance, density of stocking and, 
finally, variations in tone and texture, 
car be an indication for a particular 
forest type. An analogous statement was 
also made by de Rosayro based upon 
his experience in photo-interpretation 
in the tropical rain forests of Ceylon (4). 
D. CONSTRUCTION OF THE TYPEMAP 
The forest type boundaries indicated on the 
photographs are afterwards transferred to the 
map. For this purpose ready-made plani- 
metric maps could be used at an equivalent 
map-scale. By superimposing topographic 
features on the photograph, like drainage 
patterns, good discernible forest roads or 
other features, over the corresponding ones in 
the map, the type boundaries can be traced 
without any difficulties, especially in flat ter- 
rain. If no good maps are available, first a 
triangulation of pass-points had to be made; 
in most cases the slotted-templet method will 
be quite sufficient; for this a certain amount of 
ground-control must be available. If there are 
occasional triangulation stones in the region 
to be mapped, the situation of these pillars 
can be pinpricked upon the photographs dur- 
ing the preceding field work. 
Maps are mostly made at photo-scale or a 
scale, which is a little bit smaller than that of 
the original photographs. The last method is 
always preferable, as possible mapping errors 
are accordingly reduced. A reduction in the 
scale from the photograph to the original map 
10 
of more than two times is not advisable as, 
under such circumstances, the application of 
the normal transfer methods is much more 
difficult. If small-scale maps are desired—to 
get a better overall impression of the prevail- 
ing vegetative conditions—then such maps 
preferably should be made afterwards by 
compiling the mapping results of the original 
maps together upon a smaller scale—a tech- 
nique, which would be sometimes applied 
in Land Use Mapping projects. In such a case 
it will be advisable to avoid making the indi- 
vidual type areas too small, in order that the 
final map will not be too complicated and 
difficult to read. 
  
  
E. EQUIPMENT TO BE USED FOR TRANSFER OF 
DETAIL 
When considering which kind of plotting 
instrument would be advisable for forest 
mapping work in tropical areas, the general 
rule will hold, that the simplest solution will 
generally be the best one. In this respect with- 
out doubt, the most appropriate instrument 
for transfer of detail will be the Sketchmaster 
and in particular the construction made by 
Zeiss factory, which according to the exper- 
ieace at the ITC, is preferable to the same 
type of instrument made by other factories. 
Projection instruments have the advantage 
that the work to be done is not so straining on 
the eyes compared with the Sketchmaster, 
and that reductions or enlargements with the 
first type of instruments can be made more 
than two times. However, these instruments 
are not advisable in the tropics as the work 
could be done only in air-conditioned rooms. 
The Zeiss Stereopret, produced recently, 
proved to be no improvement when compared 
with the instruments mentioned above. 
Actually these simplified plotting instru- 
ments can be used only if the terrain is rather 
flat. For hilly terrain with moderate differ- 
ences in elevation, the limitation of the trans- 
fer within the central part of the photographs 
can give reasonable results. For mountainous 
terrain with important elevation differences 
in the same model, other, and more compli- 
cated plotting instruments are required. 
Under such circumstances, the Radial Line 
Plotter will perhaps be preferable as the most 
practical. The other instruments, sometimes 
specially recommended under such circum- 
stances, like the Stereotope, are generally too 
complicated for type mapping work. Further 
the application must be based upon more de- 
tailed information regarding the knowledge of 
the elevation of the pass-points in every 
model. Also the application of the Multiscope