Advanced
GIS
Using
ESRI ArcGIS 9.3
3D Analyst
TIN
3D Analyst
Activation
Be sure to have
activated the 3D
Analyst extension
and load the
toolbar.
Open the project
“Base 3” located in
the folder “Data 3”
3D Analyst
Elevation data
3D models are
calculated basing
upon appropriate
source data.
Basically, contours
and elevation point
are used.
3D Analyst
Elevation data
.
For more accurate
models, more data
can be used (e.g.
rivers, roads, scarps
etc.).
Almost all data can
be extracted from
topographic vector
maps (Select by
Attributes)
3D Analyst
Mask
Always be sure to
have base layers an
area significantly
larger than the
analysis mask.
Otherwise, severe
errors will occur
along the borders
3D Analyst
TIN
ArcGIS generates a
TIN (Triangular
Irregular Network) to
interpolate elevation
data and create a
vector 3D model.
Connecting adjacent
elevation points or
nodes, triangles
oriented in the 3D
space are created,
thus allowing to
have a z for every
possible x,y
Other GIS packages interpolate between vector data creating a
raster map of elevation (one elevation for each pixel)
3D Analyst
Create TIN
First of all, a TIN is
to be created
3D Analyst
Create TIN
For the first TIN, use
only Elevation
points
Check in the list of
layers the proper
one
3D Analyst
Create TIN
Height Source
i.e. the location of
the values to be
used as local
elevation.
It may be the Z
value for 3D
features or any
numeric field
3D Analyst
Create TIN
Height Source
i.e. the location of
the values to be
used as local
elevation.
It may be the Z
value for 3D
features or any
numeric field
3D Analyst
Create TIN
Triangulate as
Method to be
adopted for the
interpolations.
Points can only be
used as “mass
points”
3D Analyst
Create TIN
Triangulate as
Lines allow three
methods:
“mass points”
“hard line”
“soft line”
Generally, it is better
to use the “soft line”
method
3D Analyst
Create TIN
source data
Triangulate as
Lines allow three
methods:
“mass points”
“mass points”
“hard line”
“soft line”
Generally, it is better
to use the “soft line”
method
37
26
15
“hard line”
“soft line”
Create TIN
Triangulate as
Polygons allow
eleven methods:
“mass points”
“hard line”
“soft line”
“hard clip”
“soft clip”
“hard erase”
“soft erase”
“hard replace”
“soft replace”
“hard value fill”
“soft value fill”
3D Analyst
Create TIN
Triangulate as
3D Analyst
Polygons allow
eleven methods:
“mass points”
“hard line”
“soft line”
“hard clip”
“soft clip”
“hard erase”
“soft erase”
“hard replace”
“soft replace”
“hard value fill”
“soft value fill”
same as for lines
Removes everything outside the polygon(s)
Calculates the TIN only inside the polygon(s)
Removes everything inside the polygon(s)
Calculates the TIN only outside the polygon(s)
Replaces the TIN with the values calculated only from the polygon(s)
As before, but allows the hidden objects to be taken into account
Similar to “replace”
Similar to “replace”
Create TIN
Tag value field
An integer value can
be stored in the TIN
for every triangle
and node.
They are typically
used to store the
accuracy of each
elevation
3D Analyst
Create TIN
Result
Of course, the result
obtained using only
elevation points will
be very rough.
Therefore, it is
better to add at least
the contours
3D Analyst
Create TIN
Adding Layers
To add a new layer
to the calculation of
a TIN it is possible
either to create a
new one using all
the selected layers
of to use the “Add
Features to TIN”
tool, upgrading the
esisting TIN
3D Analyst
Add Features to
TIN
It is possible either
to upgrade the
source TIN or to
create a new one
3D Analyst
TIN
The TIN derived
from both elevation
points and contour
lines is much more
detailed.
Anyhow, errors will
affect the borders;
therefore it is much
better to include the
mask to clip the TIN
3D Analyst
TIN
The mask (polygon!)
is to be used as soft
clip (i.e. allowing to
take into account
also the features
located outside the
clip area).
Obviously, the
“Height source” is to
be set to “none”.
3D Analyst
TIN
Result
3D Analyst
TIN
Representation
It is generally better
to remove the
source features
from the
representation. If
needed, is much
better to activate the
source layer(s).
To do this, deselect
the “Edge types”
3D Analyst
TIN
Representation
Result
3D Analyst
TIN
Representation
Use a suitable color
ramp (create it, if
needed) and use a
very small “Defined
interval” (e.g. 1)
3D Analyst
TIN
Result
3D Analyst
TIN
Errors
The interpolation
procedure almost
always determines
errors, such as flat
tops and stepwise
ridges and valleys
3D Analyst
TIN
Refinement
It is possible to
ameliorate the result
including further
vector data sources,
such as those
representing the
hydrography or the
transportation
network
3D Analyst
TIN
Refinement
Obviously, streams
and roads have
varying elevations,
therefore they have
to be stored as 3D
lines (one elevation
for each node) and
the “X value” is to
be used for the
creation of the TIN
3D Analyst
TIN
Refinement
Result
3D Analyst
TIN
Refinement
Anyhow, some
errors will remain.
When an error is
due to a wrong
value stored as
elevation in a
feature, obviously it
has to be corrected
editing the wrong
figure.
3D Analyst
TIN
Refinement
Other errors simply
are the results of
triangles created
from three nodes
having the same
elevation.
To correct them, it is
necessary to create
new shapefiles
(generally, one of
points and one of
3D polylines) and
use them to
introduce new
features in order to
have a correct
interpolation
3D Analyst
TIN
Refinement
Correction Points
Smaller errors can
be corrected adding
a new elevation
point.
The elevation can
be desumed by the
contours (faster if
labeled).
3D Analyst
TIN
Refinement
Correction Lines
For larger errors, it
is generally better to
use 3D lines.
It is generally
suggested to
activate the
snapping to both
contours and
elevation points
3D Analyst
TIN
Refinement
Correction Lines
Once drawn the
line, it has to be
edited to assign its
proper elevation to
each node.
3D Analyst
TIN
Refinement
Correction
Result
This procedure is to
be repeated until a
good result is
achieved.
Remember to close
the editor before
starting the creation
of a new TIN
3D Analyst