by a Pentax
28 mm.
ilding
; have been
1 digitizer.
applied to
the external
n this way à
cartographic-
ds and to fix
approximate
computed by
approximate
s reported on
hotos.
These have
he image.
ising and are
7 topographic
lative to the
ne, has been
characterized
nts along the
t planimetri
m points is
- 16 points di
constant height (in groups of 2 or 3) the difference of height
obtained is equal to 24 mm; |
The mean values of the standard deviations for the estimated
coordinates of 33 points computed with FOTO3D are reported
in the following table:
stdev.X | st.dev.Y | st.dev.Z |st.dev. TOT
mean 21 12 9 26
rmse +24 +15 +11 +30
Table 3: Mean values obtained in the
practical experiment (in millimeters)
These values are still better then those reported in the above
statements: recall that the table values are estimated and should
be considered, with a probability of 99%, a + 3-st.dev. values.
In any case, the obtained precision is much higher than that
required in the technical specifications of a digital mapping in
scale 1:5.000.
5. CONCLUSIONS
The method proposed for the production and updating of low
cost digital cartography, to be used as the geometric database of
a GIS, proves to be particularly interesting, both from a
theoretical and from a practical point of view.
The adopted analytical model (mixed linear model) allows the
simultaneous estimation and prediction of several groups of
unknowns, so that the different reliabilities of different obser-
vations (cartographic, photogrammetric, GPS) can be
considered in the definition of a unique "datum".
The processes of georeferencing the cartographic units and
updating the map content are performed simultaneously,
exploiting the correlation created by cartographic-
photogrammetric tie points.
The instrumentation required for the application of this method
is extremely simple: as field operations a single-frequency GPS
receiver (two ones in case a fixed station is too far) and an
amateur camera are enough; then a PC for calculations, a
scanner, a digitizer and the FOTO3D software are required.
In this way, an up-to-date geometric database, having a
satisfactory precision, can be produced at low cost and in short
time, using an existing cartography and amateur photographs,
as was shown in the above example.
Through GPS control it is possible to update cartographic areas
with no cartographic particulars visible in the images, to reduce
deformations of the cartographic support and to join, if
necessary, several layers into a unique reference.
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
