For analyzing using the grid option, you need to already have two
existing grid
files. If the grids are not visible to begin with in plan view, you
will want to have them visible on-screen using the Draw 3D Grid File
command. The grids should overlap
with the same location and resolution. The resulting red/blue map with
legend is
shown below.
No mapping is calculated on tin or grid cells that extend beyond the
extent of the data. Extrapolation can be
used to calculate elevations for the grid cells that are beyond the
data limits. The prompt
Extrapolate grid to full grid size? shows when there are grid
cells with no elevation in a grid (.GRD) file. Extrapolation fills in
all
the grid cells. The method to extrapolate uses a safe calculation that
tends average out or level the extrapolated values. So extrapolated
grid areas are not as accurate as
grid areas within the limits of the data.
For a color map showing differences between triangulation mesh files:
Type of surface model source [Tin/<Grid>]? T
Select Base Triangulation File Dialog Select an existing
.flt or .tin file
Select Design Triangulation File Dialog Select
a second existing .flt or .tin file
Select the Inclusion perimeter
polylines or ENTER for none. pick a closed polyline
Select the Exclusion perimeter
polylines or ENTER for none. press Enter
Pulldown Menu Location: Grading
Keyboard Command: cf_map
Prerequisite: Two grid (.GRD), triangulation mesh (.FLT) or
tin (.TIN) files
File Names: \lsp\contour4.arx, \lsp\volcalc.arx