Local-Level INS Simulation:
As an introduction to the capabilities of the INS Toolbox,
consider a simplified three-dimensional INS simulation.
The toolbox function PROGEN
generates three-dimensional flight profiles in a locally
level coordinate system. The toolbox functions GENDV and
GENDTHET take the output of PROGEN and generate ideal, error-free
delta-V's and delta-theta's (note that these are the components
due to vehicle motion relative to the local-level coordinate
frame only. Earth rotation and Coriolis effects are handled
separately. See the sections on
sensor error simulations
and great circle path simulations:
with Sensor Errors).
The inertial processing of the "measurements" first involves initializing
position, velocity and attitude. For the moment we will assume that
the initialization has been accomplished without error. The next
steps (which are performed for each measurement epoch) involve 1)
using the toolbox function BODUPDAT to update the body-to-nav
direction cosine matrix (attitude representation); 2) using the
updated direction cosine matrix to translate the delta-V's from
the body-frame to the local-level frame; 3) accumulating the
translated delta-V's to update velocity and 4) integrating velocity
to update position.
A demo program which performs the aforementioned tasks is provided
with the toolbox. On a global scale, the result of the inertial
processing is virtually identical to the original flight profile.
There are errors, however, due to imperfect integration. The errors
are small but measurable:
It is apparent from the plot that multiple sampling rates were employed.
Staight segments do not need to be sampled as often as turns and other
dynamics and the toolbox supports multi-rate simulations.
Another example given in the toolbox is a repeat of the above
example but with time steps cut in half. The results, as expected,
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