How To Create a TIN Surface in Civil 3D

To Create a TIN Surface

1.    Click Home tab Create Ground Data panel Surfaces drop-down Create Surface   .

In the Create Surface dialog box, in the Type list, select TIN Surface.

2.    Click   to select a layer.

Note: If you do not select a layer, the surface is placed on the current layer.

3.    In the properties grid, click the Value column for the Name property and enter a name for the surface.

Note: To name the surface, click its default name and enter a new name, or use the Name Template.

4.    To change the style for the surface, click the Style property in the properties grid and click   in the Value column.

The Select Surface Style dialog box is displayed.

5.    To change the render material for the surface, click the Render Material property in the properties grid and click   in the Valuecolumn.

The Select Render Material dialog box is displayed.

6.    Click OK to create the surface.

The surface name is displayed under the Surfaces collection in the Prospector tree.

LESSON NOTE ON MAP

WHAT IS A MAP?

Introduction

1. Even from the earliest days the urge for man to explore has been great. The early travellers used natural features to help them find their way from place to place.

By noting the position of the stars, the moon and the sun, man devised a method of finding out where he was. This meant exploration past known boundaries was now possible. As the explorer ventured further and further from home and recognizable features disappeared, he would often sketch his surroundings so that the way home could be found more easily. These early ‘maps’ where often drawn on animal hide, stone or reed paper.

2. If we think of the earth as a sphere, we can imagine how it could be covered with imaginary lines to help pinpoint a position on the surface. First of all the earth has an axis, running from the True North pole to the True South pole - the only 2 points on earth that do not rotate. Next, imagine a line that runs around the middle of the earth half way between the North and South poles- this circular line is called the equator.

3. If we add more lines running parallel to the equator, they will also be circular, though smaller than the equator; they are called lines of latitude. Lines on the Earth’s surface drawn from pole to pole are called lines of longitude.

Longitude

4. Longitude lines, also called meridians, are circular. They are numbered and have a starting point at Greenwich in England. This line is numbered zero and called the prime meridian- all other lines are either east or west of it. Every meridian from one pole to the other - is a semi-circle, and has an anti-meridian on the opposite side of the earth. A meridian and its anti-meridian together make a full circle round the earth.

5. By numbering the lines, it means that the whole of the earth can be covered.

The position of each line is expressed in degrees away from the prime meridian.

For example in the diagram point ‘A’ is about 20° (degrees) west of the prime meridian. Point ‘B’ is about 40° east of the prime meridian. Although this system can give reasonably accurate positioning it is not accurate enough for everyday use, so each degree is further broken down into 60 minutes. This now gives us a system of describing a point’s location in terms of degrees and minutes either east or west of the prime meridian (Greenwich).

Latitude

Lines of Latitude

6. Lines of latitude are circles drawn around the earth, parallel to the equator.

The equator, at zero degrees, splits the earth into two halves, the northern hemisphere and southern hemisphere. Using the lines of latitude you can describe any point’s location in degrees and minutes either north or south of the equator.

LESSON NOTE ON MAP READING

MAP READING

WHAT IS A MAP?

1. Once you have selected your map - HOW do you use it?

It is necessary that the cadets know the following points in connection with the subject.

Planning is a very important part of any activity and time should be spent on getting to know the

area you intend to go. The sort of things to look out for are those features which stand out on the

map and would be easily recognisable on the ground. This is particularly useful if you or your party run into problems - remember your reaction will be quicker if you familiar with the map.

Once you are happy with your map and feel confident to use it you need to go out and gain some experience of comparing the map to the ground area. This may be achieved in towns, cities or local country side. Any map may be used even a street map as long as it gives the cadets practice in moving from one point to another.

2. If you look at any atlas of the world, you will get a good idea of how continental landmasses

lie compared to oceans. When the surface of the earth is shown on a flat piece of paper some

distortion takes place. You can spot errors of distortion if you look closely. For example Greenland is shown to be larger than India but in fact India is approximately four times the size of Greenland.

This happens because the surface of the earth is stretched at the poles and squeezed at the

equator to make it lie flat.

Maps tend to be accurate in shape and position (bearing) - they are inaccurate as far as distance

and area are concerned.

To allow more detail to be shown the world map can be broken down into many single sheet maps. You might think of it as using a microscope with the world under the lens. The more you zoom in the clearer the picture becomes and the more accurate the image you get.

3. To make map reading more enjoyable and to make cadets think, you may like to try some

of the following ideas.

a. Blindfold a cadet and then pace out a set distance in a straight line. Make a note of how

much drift there is and in what direction it was.

b. Have one cadet blindfolded and have another direct the first through a small obstacle

course (using paces and direction only).

c. Have the cadets draw a map of the town/village or city centre (from memory) then compare

the results to an actual map.

d. Try comparing old maps to new ones to see what changes have taken place in your

area.

e. Mark out a route on an aerial photograph and have the cadets follow it.

f. Use different types of ground to find out different pace numbers and times i.e. 100m on -

paths, road, tracks, bracken, heather, sand, uphill and downhill.

4. Map reading can be fun but it also has a serious side. If you decide to go out for a walk

locally it is possible to get lost. A map can be a good friend to you when you are out walking – don’t leave home without one!

There are many types of maps in general use. Different types of map depict different types

of information. Although maps tend to suit a specific user, different types of map can sometimes be used by different groups. For map reading in the Corps the important factor is scale. The many types of map available on the market reflect the wide range of activities for which maps are needed.

Motoring atlas of the UK 1 inch to 3 mile scale

Cycle tours 1:50,000 or 1.25 inches to 1 mile

Explorer maps 4 cm to 1 Km or 2.5 inches to 1 mile

Pathfinders maps 4 cm to 1 Km or 2.5 inches to 1 mile

Coast to Coast maps

Travelmaster map 1 inch to 4 miles

Waterway guides

Outdoor Leisure maps 4 cm to 1 Km or 2.5 inches to 1 mile

National Trail guide 1:25,000

Historical maps and guides 1 cm to 25 cm or 25 inches to 1 mile

World Atlas

Local authority maps

Air maps

Agricultural maps

Marine maps

Political maps

There are now available CD-ROMS that contain information that you can interrogate, zoom

in or ‘walk’ through in detail.

Lesson Note On Digital Terrain Model (DTM)

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.

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 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.

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.

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.

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.

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.

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.

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.

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.