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NUMERICAL INTERPOLATION IN FLIGHT SIMULATORS FOR
MICROCOMPUTERS USING DIGITAL ELEVATION MODELS
Ricardo Rodrigues Rangel
Instituto de Estudos Avangados - IEAv - CTA
12.2317990 =
Sáo José dos Campos - SP
rangel@ieav.cta.br
Luiz Alberto Vieira Dias
Instituto Nacional de Pesquisas Espaciais - INPE
12.227-010Gr
Sáo José dos Campos - SP
vdias@ltid.inpe.br
KEYWORDS: DEM/DTM K122, Simulation K101, Software K165
ABSTRACT:
This work presents Numerical Interpolation applications for Flight Simulators terrain
visualization. The terrain may be synthetic or real, obtained through Digital Elevation
Models. Using Computer Graphics techniques,
reasonable realistic results. The Geometric Transformations and Interpolations must be
sufficient fast and precise, in order
performance.
1. INTRODUCTION
A Flight Simulator; has the’ purpose to
simulate the several steps of a real
flight in a icomputational 'environment.
Basically it consists of an animation
over a Digital Elevation Model (DEM) ,
where the model movement simulates the
airplane movement.
If «the purpose is .to .simulate in. real
time, the frames have to be displayed
faster than the human vision can
perceive, or about 24 frames per second (
as in motion pictures).
In Computer Graphics the terrain is
represented by regular, or irregular
grids, with, the grid points representing
the terrain altitude. For microcomputers
the number of samples have to be kept to
a minimum. The sampling of the altitude
points may be obtained from maps of by
photogrammetry.
2. NUMERICAL INTERPOLATION
It is important that the numerical model
could reproduce the original terrain with
certain fidelity. If microcomputers are
used, due to memory and speed
limitations, the number of samples have
to be kept to a minimum, so the
interpolators used have to be very fast
that the
907
it is possible to generate animations with
Simulator would achieve a good
and reliable. The main, purpose is to
reconstruct the terrain, with the minimum
possible points, and with the maximum
fidelity. In this paper it will be used a
regular grid.
Let's briefly recall some interpolation
methods. The linear interpolators are
very fast, and, if the number of samples
enough, the results are very good.
However for insufficient sampling the
results do not resemble the reality. In
this paper the linear interpolators were
used for illumination, shading and
rendering of the frames.
The Akima interpolator, on the other
hand, is also very fast, and does an
excellent work in terrain reconstruction.
It has partial second derivatives
continuity on the patches junctions (
Akima, 1974). This interpolator was used
in this paper for the reconstruction of
the sampled grids.
As an example Figure 2.1 below presents
the result of the interpolation, by
several methods, of a real terrain
(region centered on 41925'N and
74959'W, on the Hudson Valley, near West
point, VA, USA), with a 11 = 11 points
grid with a spacing of 209.46 meters on
the E-W direction, and 277.53 meters on
the N-S direction. the altitude range in
the real terrain is from 0 to 394 meters.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996