Digital Terrain Model (DTM)
A digital terrain model (DTM) is a mathematical model of a project
surface that becomes a three- dimensional representation (3D) of existing and
proposed ground surface features. Critical calculations and processes based on
the DTM include contouring, cross sections and quantities, drainage models,
watersheds, hydraulics, water catchment areas, and cross sections sheets.
surface that becomes a three- dimensional representation (3D) of existing and
proposed ground surface features. Critical calculations and processes based on
the DTM include contouring, cross sections and quantities, drainage models,
watersheds, hydraulics, water catchment areas, and cross sections sheets.
A DTM is created through the construction of a Triangulated
Irregular Network (TIN) and is based on modeling the terrain surface as a
network of triangular facets that are created by simply connecting each data
point to its nearest neighboring points. Each data point (having x, y and z
coordinates) is the vertices of 2 or more triangles. The advantage of the TIN method
is its mathematical simplicity- all DTM calculations are either linear or
planar.
Irregular Network (TIN) and is based on modeling the terrain surface as a
network of triangular facets that are created by simply connecting each data
point to its nearest neighboring points. Each data point (having x, y and z
coordinates) is the vertices of 2 or more triangles. The advantage of the TIN method
is its mathematical simplicity- all DTM calculations are either linear or
planar.
The processes and the resulting DTM offer many advantages over a
topographic survey. Field data for a DTM is collected in a way that allows
TxDOT to use the latest in automated survey technology. Traditional data
collection (for a topographic survey) involves taking cross sections, typically
every 100 feet, along a horizontal control line or in a grid pattern. Digital
terrain modeling has virtually eliminated this practice.
topographic survey. Field data for a DTM is collected in a way that allows
TxDOT to use the latest in automated survey technology. Traditional data
collection (for a topographic survey) involves taking cross sections, typically
every 100 feet, along a horizontal control line or in a grid pattern. Digital
terrain modeling has virtually eliminated this practice.
Data points (shots) are taken at every break in elevation with no
particular pattern being required. The emphasis is on identifying all features
and changes in elevation within project limits. Data is collected using an
electronic data collector with an electronic total station. The data points are
assigned feature codes, attributes, descriptions, comments, and connectivity
linking codes to add intelligence to a point at the time of data entry into
data collector.
particular pattern being required. The emphasis is on identifying all features
and changes in elevation within project limits. Data is collected using an
electronic data collector with an electronic total station. The data points are
assigned feature codes, attributes, descriptions, comments, and connectivity
linking codes to add intelligence to a point at the time of data entry into
data collector.
Information is downloaded from the data collector to a computer,
either in the field or later in an office, and is processed using AASHTOWare® Survey
Data Management System®(SDMS) software. A SDMS® calculated
file is generated for importation into CAiCE™ or GEOPAK Survey™ for
further review. The file is then imported into GEOPAK® for
project design.
either in the field or later in an office, and is processed using AASHTOWare® Survey
Data Management System®(SDMS) software. A SDMS® calculated
file is generated for importation into CAiCE™ or GEOPAK Survey™ for
further review. The file is then imported into GEOPAK® for
project design.
Digital Terrain Model (DTM)
A digital terrain model
(DTM) is a mathematical model of a project surface that becomes a three-
dimensional representation (3D) of existing and proposed ground surface
features. Critical calculations and processes based on the DTM include
contouring, cross sections and quantities, drainage models, watersheds,
hydraulics, water catchment areas, and cross sections sheets.
(DTM) is a mathematical model of a project surface that becomes a three-
dimensional representation (3D) of existing and proposed ground surface
features. Critical calculations and processes based on the DTM include
contouring, cross sections and quantities, drainage models, watersheds,
hydraulics, water catchment areas, and cross sections sheets.
A DTM is created through
the construction of a Triangulated Irregular Network (TIN) and is based on
modeling the terrain surface as a network of triangular facets that are created
by simply connecting each data point to its nearest neighboring points. Each
data point (having x, y and z coordinates) is the vertices of 2 or more
triangles. The advantage of the TIN method is its mathematical simplicity- all
DTM calculations are either linear or planar.
the construction of a Triangulated Irregular Network (TIN) and is based on
modeling the terrain surface as a network of triangular facets that are created
by simply connecting each data point to its nearest neighboring points. Each
data point (having x, y and z coordinates) is the vertices of 2 or more
triangles. The advantage of the TIN method is its mathematical simplicity- all
DTM calculations are either linear or planar.
|
Table
4.4 TSPS Manual of Practice Chart for Tolerances for Conditions |
|||
|
Condition
|
I
|
II
|
|
|
|
Urban
Business, District Urban, Suburban & Industrial |
Rural
& Broad Area General Mapping |
Remarks
& Formulae |
|
Error in Traverse Closure
|
1:10,000
|
1:7500
|
System
Control Loop |
|
Unadjusted Level Loop Closure (ft.)
|
.04
|
.08
|
System
Control Loop M=Miles |
|
Secondary Traverse Closure
|
1:7500
|
1:5000
|
Between
System Control Points |
|
Secondary Level Loop Closure (ft.)
|
.05
|
0.2
|
Between
System Control Points |
|
Positional Error of Any Primary Monument
(horizontal) |
1:15000
|
1:10000
|
For
monuments used for Triangulation or Radial Surveying in respect to another |
|
Positional Error of Any Primary Monument
(vertical) |
±
.03 ft. |
±
0.15 ft. |
For
permanent bench marks |
|
*Contour Interval
|
2
ft. |
10
ft. |
Or
as needed by the State |
|
Contour Accuracy
|
±
½ Contour Interval |
±
½ Contour Interval |
|
|
Positional error of any Photo Control Point
(horizontal and/or vertical) |
0.50
ft. |
2
ft. |
Or
as recommended by Photogrammetrist |
|
Location of Improvements, Structures, and
Facilities during survey |
±
0.05 ft.
±
0.50 ft. |
±
0.1 ft.
±
1 ft. |
Vertical
(inverts, flow lines)
Horizontal
|
|
Plotted location of Improvements, etc.
|
±
1/40 in. |
±
1/40 in. |
Symbols
may be used for large scale maps indicating Center point |
|
Scale of maps sufficient to show detail, but
no less than |
1”
– 200′ |
1”
– 2000′ |
Drawings
are to show location of survey monuments and bench marks |
The processes and the
resulting DTM offer many advantages over a topographic survey. Field data for a
DTM is collected in a way that allows TxDOT to use the latest in automated
survey technology. Traditional data collection (for a topographic survey)
involves taking cross sections, typically every 100 feet, along a horizontal
control line or in a grid pattern. Digital terrain modeling has virtually
eliminated this practice.
resulting DTM offer many advantages over a topographic survey. Field data for a
DTM is collected in a way that allows TxDOT to use the latest in automated
survey technology. Traditional data collection (for a topographic survey)
involves taking cross sections, typically every 100 feet, along a horizontal
control line or in a grid pattern. Digital terrain modeling has virtually
eliminated this practice.
Data points (shots) are
taken at every break in elevation with no particular pattern being required.
The emphasis is on identifying all features and changes in elevation within
project limits. Data is collected using an electronic data collector with an
electronic total station. The data points are assigned feature codes,
attributes, descriptions, comments, and connectivity linking codes to add
intelligence to a point at the time of data entry into data collector.
taken at every break in elevation with no particular pattern being required.
The emphasis is on identifying all features and changes in elevation within
project limits. Data is collected using an electronic data collector with an
electronic total station. The data points are assigned feature codes,
attributes, descriptions, comments, and connectivity linking codes to add
intelligence to a point at the time of data entry into data collector.
Information is downloaded
from the data collector to a computer, either in the field or later in an
office, and is processed using AASHTOWare® Survey Data Management System®(SDMS)
software. A SDMS® calculated
file is generated for importation into CAiCE™ or GEOPAK Survey™ for further review. The file is then
imported into GEOPAK® for
project design.
from the data collector to a computer, either in the field or later in an
office, and is processed using AASHTOWare® Survey Data Management System®(SDMS)
software. A SDMS® calculated
file is generated for importation into CAiCE™ or GEOPAK Survey™ for further review. The file is then
imported into GEOPAK® for
project design.
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