ISOMAP
is the module that is used to calculate and render surfaces through
contour lines or coloured and shaded areas with a high degree of
precision.
The
program allows the representation of the surface both in topographic
map and perspective view forms.
The calculation is performed in two stages.
The
first stage consists of creating a regular grid from a collection
of arbitrarily positioned points.
The
second stage consists of drawing the surface using the previously
created grid.
The first stage can be performed using three methods: the inverse
distance method, the kriging method, and a new interpolation and
extrapolation method based on a weighted average of polynomial surfaces.
The
use of this polynomial algorithm makes it possible to generate points
that are external to the area of the sampled locations in such a
way as to maintain the trend of the surface, even when this surface
cannot be approximated by a simple horizontal plane.
This feature is especially useful for those problems that deal with
the surface gradient, such as flow line tracing or rockfall analysis.
The commonly used extrapolation algorithms based on the weighted
average (including kriging) can lead to large errors, for example
to the inversion of the flow direction in the peripheral areas of
the map.
The
use of a polynomial algorithm to create a grid also yields a more
realistic surface of the area where the sampled locations can be
found, as the evaluation is less sensitive to the spatial distribution
and point density.
The regular square grid is then interpolated with bicubic splines
to obtain a continuous surface that is continuously differentiable
and which passes through the grid nodes.
The
ISOMAP module has the following basic operations:
 Grid
Generation
 Slope
Map
 Exposure
Map
 Grid
Difference
 Linear
Transformation
 Filtering
 Grid
Duplication
 DTM
Import
There
are commands to execute transformations and operations between models
(conversion of measurement units, linear transformations, construction
of contour lines related to thickness and depth) and specific commands
for the treatment of gravimetric and magnetometric data, such as
the separation, obtained through digital filtering, of the local
and regional anomalies.
The
user can structure equidistances and the graphic quality of the
contour lines.
Flow
lines or vectors can be inserted to represent gradients or the dip
direction. The representation can be limited to certain intervals
and/or areas.
The
program enables the generation of Map, Wireframe View, or Solid
View. The view point distance and light vector can be determined.
