- to establish, also, a methodology of intervention which
renders to the maximum the survey potentiality;
- to test the difficulty in the processing data, in the corrections
and in their transfer from GPS to GIS (ARC-View 2.1 in our
case) and eventually assess the correct procedure of data
transfer,
- to verify performance time in general of the informatic
process from differential corrections to the cartographic
production and to test the technical! level necessary to carry
out each operation;
- the search of an adequate format of digitization (and
consequent filing) of photographic material which would
consent running on PC programs without reducing
excessively the informative contenta;
- construct a digital terrain model starting from GPS data and
through this make corrections and georeferencing of the
archived photographic material; :
- to relate between these and different types of data the
archived photogrammes to make query procedures of a
complex type;
produce cartographic process for use in planning (particularly
the creation of an orthophotomap 1:10.000 scale of the areas
burnt up by fires to use in the studies of the dynamics of fire
propagation).
Equipment and methods
Base
The Trimble Pathfinder Mapping System was used for the
GPS survey. In particular the 12 channel Community Base
Station was used as a reporting station for differential
corrections. It receives signals from 12 setellites and makes
the necessary corrections to insure sub-metric precision
measuring in post-processing. This station is set up iuside the
Department of Planning, Planning and Environment of the
Emilia Romagna Regional Administration and is connected to
a Compact Dome receiver aerial stabilised in a precise position
in a free field of ‘vision over the top of the building. It is
activated when necessary and is used for all the GPS survey
activities of the Landscape, Parks and Natural Heritage
Administration. The base was found at about 20 km from the
operating point during these tests, so guaranteeing sub-metric
precision when surveying.
Rover (GPS mobile)
The rover which was used is a Trimble Pro XL implemented
with a datalogger CMT MC-V. The ProXL is an eight channel
receiver which works both in Real Time and Post Processing
modes, and using this last mode it is able to give a sub-metric
precision.
The datalogger CMT MC-V (implemented with IMB of
memory in the version we used) was chosen for its extreme
hardiness and was designed to be used in all types of
environmental conditions, it permits the management of
personalized databases to store data during survey.
Aerophotographic instruments
The two areas under examination were singled out in two
pairs of stereoscopic photogrammes (colour slides), being part
of the shots, 1:13.000 average scale, of the 1974-1976
Regional Administration coverage actualised for the
“production of technical cartography in 1:10.000 and 1:5.000
scale. This material was chosen not only for its use in the
production of regional cartogrephy but because it was
included in the phase of remote sensing for the Regional
Foresters Inventory and was therefore, free of charge,
immediately at the disposal of the forestry technicians, making
it ideal for fixing operative methods at low cost. The use of
these photogrammes was not compromised by their age, as the
forest typologies involved in fires ara stable and have not
changed over the past twenty years. Further more, the use of
old but availeble materiel proved to be useful in calibrating, in
en extremely precise way, the real operative possibilities of the
system. na
The whole informaric sector involving the processing of the
photogrammes was carried out a personal Computer Compaq
486 50 Mhz. The choice of working on a PC was necessary to
keep low level costs of managing and also to keep the
operative difficulties at equally low levels.
It is foreseen that the user can be not only the not
exceptionally skilled personnel, but also a technical staff in
possession of only a basic knowledge of informatics,and they
can be the exclusive users of this type of equipment.
Survey
The procedure methods of the GPS zurvey, one for each area,
was carried out over two days (11th and 22nd August 1955).
Immediately before undertaking the survey, preliminary work
was done (assignment planning and check in of the land
equipment). The forest fire survey was effected by two
Regional technicians assigned to GPS and by a team of CFS as
guide and controller of the results, The GPS technicians
covered, on foot, the whole perimeter of the two fires and
implemented the information in database during the march.
Walking back at the end of the survey, an observation was
made of the principle road conditions (SS64) end of the
access to the burnt areas (known datum was chosen for its
verified instrumental precision which is necessary for the
rapid cartographic positioning).
This procedure was carried out by positioning the aerial GPS
. on the roof of the car (using the suitable magnets supplied)
and storing a series of descriptive data en route.
DPGS
The differential corrections were calculated in post processing
immediately on return to base, using software Pfinder
equipped with ProXL system. After the corrections were
made, the geographic co-ordinate of various points were
transformed from DATUM WGS84 (approved GPS system) in
ED50 UTM projection with the scope of rendering the survey
overlay possible on the existing cartography.
The technique of differential corrections was chosen for post
processing work as, when it is not necessary to work within a
certain time and then connect it via radio to the rover base,
this technique makes the survey procedure quicker and
economical.
Photogrammeter processing
The slides were digitized using a 600 d.p.i. scanner limiting
collecting to the concerned areas, in such a way as to minimise
the processing time. Seeing that the morphology of the aree
concerned presented not indifferent variations of quote, the
simple production of a digital photoplan did not guarantee 2
sufficiently correct representation. For this reason
ORTHOMAP (SISCAM) software was used.
The images were orientated externally using the “space
resection" method, giving the ‘system the focal point of the
photocamera used for the shots and a sufficient number of
visible co-ordination points on the image. The software,
therefore, processed the initial images in function of the poinis
296
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
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