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AutoCAD as a basis for railway system civil

engineering design

G. Kokalanov

Faculty of Civil Engineering,

St. Cyril and Methodius University, Skopje, Macedonia

Abstract

In the paper will be presented a computer program for designing andmanufacturing of civil engineering railway. The program is based on AutoCADtechnology. The program is designed to be modular and resource-sharing,allowing the greatest flexibility and efficiency. In the design process it is veryimportant to have quality and reliable information. Many resources and methodsare implemented in the program in order to create a good layout. The mainhorizontal and vertical elements are defined in accordance with trafficconditions. Some modification of the main elements, in order that the railroadbest suits the terrain, can be done be using of editing tools. The preview optionspromptly display the corrections, allowing the customer to have full control ofthe editing process. The generation of a normal cross-section is automaticallyperformed. The cutting and fill areas are also calculated automatically andsaved in a database for later calculation of total volumes. ArcCAD is used as adevice which makes GIS relation database transparent from/to AutoCAD.

1. Introduction

Many civil engineering railway design packages, with high performances, existin the world. In many cases these packages are not user-friendly. The customershave to spend hours to learn how to use them. When the package is usedperiodically, working with these packages is practically uncomfortable. Nationaltechnical standards which are different in many countries, needs somemodifications of the standard packages. It is very possible that someone'srequirement for modification of the program will be refused by the developer ifthe number of licences is limited.

Transactions on the Built Environment vol 18, © 1996 WIT Press, www.witpress.com, ISSN 1743-3509

24 Computers in Railways

On the other side, almost every designing bureau has equipment and staffsskilled to work with AutoCAD. Our idea was to develop a program which willwork in an environment that is not strange to customers; the environment inwhich they will feel comfortable. AutoCAD is very popular all around theworld. The graphical interface makes the program easier to learn and use. Wethought that it is logically to choose AutoCAD as basis for railway system civilengineering design.

The program was developing having in mind these main strategic points:• to be easy to learn and use• to be robust and stable• to be open for adaptation and translations

All the time we have had in mind the fact that everyone's needs couldn't besatisfied precisely - many companies have their own standards, and eachdraftsperson or designer has his own work style. One way to make the programwhich will suit everyone's needs was to use AutoCAD's open architectureapproach. It enable the programmer to create many extend features to suiteveryone's requirements.

The AutoCAD Development System (ADS) , a C-language programmingenvironment, was used to develop this AutoCAD application. The ADSapplication was not written as a stand-alone program. It is a set of externalfunctions that are loaded by, and called from AutoCAD. The applicationdefines many new AutoCAD commands. When the application has been loaded,an external command can be invoked exactly as a built-in command.

An ADS application is for the most part functionally equivalent to anapplication written in AutoLISP, (natural language for design CADapplications). Why did we make a decision to use ADS rather than AutoLISP?ADS applications tend to be more efficient in terms of speed and memoryusage. They can also directly access some facilities that AutoLISP cannot, suchas the host operating system and hardware. This makes them well suited forapplications that require considerable computations or interaction with hostenvironment. On the other hand, they can be more time consuming andexpensive to develop and maintain. Like AutoCAD itself, they require adifferent executable version for each supported platform, and development toolsmust be purchased separately for each platform. AutoLISP is better suited forapplications where maintenance and development costs are more importantconsiderations than performance. Generally speaking the choice of whether touse AutoLISP or ADS is up to the developer. The main reason why we choseADS was that we already have had a lot of experience in C programming.

With the new versions of AutoCAD, customers can very simply design andimplement their own dialogue boxes. Support for dialogue boxes is independentof the hardware and operating system. The behaviour of a dialogue box remainsthe same across all platforms, while its appearance changes to that of platform'sgraphical user interface. The design of dialogue boxes is defined in ASCII textfiles written in Dialogue Control Language (DCL) Many AutoCAD functions


Computers in Railways 25

for handling dialogue boxes were created in the program. They are used tomake interface between customer and program. The use and behaviour of theprogram is controlled by these dialogue boxes.

The program is designed to be modular and resource-sharing, allowing thegreatest flexibility and most efficient use of resources.

2. Initialisation

The first module is INITIALISATION. It is used to insert all necessary layers,create blocks and set program's variables.

The data created and used by the application are stored in an externaldatabase. In the process of initialisation, the customer has to input informationon where the database is. AutoCAD SQL Extension (ASE), a StructuredQuery Language interface, is used to make interface between data used bydifferent modules. Using the ASE interface, graphic entities in AutoCADdrawing are associated and linked with records in the external database. Theprogram contains custom SQL applications that enable communication withexternal database management systems from within AutoCAD. The databasecan be created and manipulated outside AutoCAD by the same databasemanagement systems. After that, it can be used for creation and manipulation ofAutoCAD entities.

3. Layout

In the design process it is very important to have quality and reliableinformation. Many resources and methods can be used to create a good layout.Some of the methods are implemented in the program. Also existed some third-party product with high performances, which was running inside AutoCAD Forexample Quicksurf is a fast, powerful general purpose surface program. It isused for generation and annotation of contour maps, profiles, sectional andvolumetric computation. By making appropriate interface, the customer caneasily transfer data created by Quicksurf and the application.

Surface sampling methodsAn infinite number of points can be used for modeling of a surface. A samplingmethod must be used to extract representative points to build a surface modelthat realistically approximates the actual surface. A surface model should:

• Accurately represent the surface• Be suitable for efficient data collection• Minimise data storage requirements• Maximise data handling efficiency• Be suitable for surface analysisThree methods are used to represent surfaces in digital form: contour lines,

arrays of equally-spaced sample points, and irregularly-spaced sample points.



Contours Contours are lines that follow paths of constant elevation on themodeled surface, They are the most familiar representation of terrain surfaces.Contour accuracy depends upon whether the isolines have been generated fromprimary or derived data. When contours have been generated from aerialphotographs as primary data using a stereoplotter, the contours are highlyaccurate. If the contours have been generated from point data, the location ofthe contours must be interpolated between known values. One of the majordrawbacks of contours is that they only indicate surface values along the isoline.Surface anomalies between contour intervals cannot be represented. Once thesurface has been represented as contours, interpolation can be used to derive anelevation for locations between contours. This interpolation is performed bysolving polinomial equations representing known Z values.

Digital Elevation Models is another digital format for representing a surface. Itconsist a set of vertices, spaced rectangularity in the X and Y directions, with Zvalues conforming to the modeled surface. The Z value at specific point can beapproximated by interpolation between adjacent sample points. As a smallergrid cell size is used, any error between the input data set and the calculatedgrid is reduced. Girding is very effective when dealing with data sets that do notcontain break data. Because the samples are points, surface features such asstreams and ridges cannot be represented directly by the sample array. Similarly,surface anomalies such as peaks and pits can be missed.

Figure 1 Digital Elevation Model

Point arrays representing the surface of the Republic of Macedonia are notreadily available in Macedonia . Using Sat el SPOT Images, DEM at severalresolutions, will be created very soon. Digital Elevation Models can be createdby special-purpose programs (Arc/INFO, ERDAS ..). Drawing interchange files(DXF) created by these programs, can be used to turn DEM into AutoCAD'sdrawing files. This mechanism accomplishes very easy transferability ofinformation between AutoCAD and other special programs. In the next versionof the program, we are going to include an option which will allow direct accessto the database created by this special-purpose programs.

Irregular networks The triangulated irregular network, or TIN, is a three-dimensional model of surface composed of planar triangular faces. It is



generated by using the Delauney criterion. The points are connected optimallyto make all triangles as nearly equilateral as possible. The TIN (triangulatedirregular network) concept was devised for representing surface efficiently. Asurface can be approximated by combining irregularly spaced points, lines andpolygons. These point and line features correspond to peaks, pits, passes, pointsof change in slope, railroad edges, stream channels, and shorelines. Thesampling points can be located at optimum locations. TIN accurately representsa surface with less points than other data models. Three-dimensional irregularlyspaced data comes from wide variety of sources.

TINs and grids can be created from data in ASCII formats. TINs can becreated from one or more ASCII files containing points, lines, breaklines andboundary polygons. Files can be thematic; for example, one file may containsampling points used for surface modeling; the other can contain lines whichrepresents rivers and so on.

Figure 2 Triangular Irregular Network

Building TINs from contour maps is one of the most common methods ofbuilding surface models for regions where elevation data are not available indigital form. Contour data are input as layers which have been created by eitherscanning or manually digitizing contours from hardcopy manuscripts.Unfortunately, contours data are also one of the most difficult data sources withwhich to build a good TIN. Creating a good TIN from contours involves anunderstanding of the principles of surface sampling and of the potential forgenerating flat triangles on terrain that are not actually flat.

There are three basic approaches to inputting contour data from hardcopymanuscripts: scanning, contour digitizing, and intelligent point selection.

Scanning contours Scanning can be a cost-effective method for convertinghardcopy contour maps to digital form. When hardcopy contour maps arescanned, all features are rasterized, including any non-contour data, smudgesand defects that may be present on map. After scanning, any non-contourfeatures captured during scanning must be identified, and removed. All theraster cells defining contour lines must be identified and vectored. This can bedone manually or interactively using line following process. The VECTORprogram, which is running inside AutoCAD, can be used to convert the scanneddata to contour line layer. Other third-party specialised software programs arealso available forms for converting scanned data contour lines.



Digitizing contours The contour digitizing approach involves digitizing of everycontour line, capturing inflection points along the line. This is done with littleconsideration for the sampling interval along the contour or the significance ofeach sample point in terms of describing the behaviour of the surface. From thedigitizing technician's point of view, this approach is the easiest method forcapturing contour data, because the operator is not required to have anunderstanding of the concepts of surface modeling. The digitized contours canbe used directly without first generating a surface model from the data. If somemore sophisticated analyses are needed, a TIN surface model has to be created.If there were areas on the manuscript which were likely to generate invalid flattriangles, additional sample points have been needed to supplement the contourswith.

Intelligent point selection The intelligent point selection approach relies uponthe operator to intelligently select sample points which best represent thesurface morphology. Most surface modelers attempt to keep the number ofselected sample points low; this reduces the time required to perform digitizing.Typically, the sample points are best pre-selected before digitizing. The surfacemodeler has to consider each sample point in context of all of its neighbouringsample points. The goal is to identify points that will generate triangles withrelatively uniform surface behaviour in term of slopes and aspect, while at thesame time avoiding the generation of flat triangles. The triangulation is furtherused for surface analyses or contours generation.

4. Axis

The module AXIS is used for construction of the main (horizontal) elements. Atthe beginning, the terrain map should be put in the background of the drawing.In that case the customer has Rill control of how the thoroughfare suits theterrain. The terrain map can be created by module LAYOUT or by scanning andvectorisation process. Some designers practice to use the initial polyline(polyline with constant inclination) as orientation in the process of constructionof the horizontal solution. Special tool for construction of the initial polylinewas created.

In the next step, the constructor draws the main horizontal directions. Thisis a polyline which can be drawn manually or by using the data stored in thedatabase. With selection of the polyline, a process for automatic generation ofthe main elements is activated. The main elements are defined in accordancewith traffic conditions. Some modification of the main directions and mainelements, in order that the railroad best suits the terrain, can be done. Someediting tools for that purpose are derived. The preview options promptly displaythe corrections, allowing the customer to have full control of the editingprocess. The program check the made correction and appropriate warnings andmessages are display if something is not in accordance with the nationalstandards.



Figure 3 Horizontal element disposition

When the main elements are created, the labels of the main element andchanges are set. The cross-axes along the longitudinal axis may be placed onequidistant distances or the intervals for placing the cross-axes can be read fromthe file. Some data are recorded in the database for later reading by the othermodules. After defining the longitudinal section, the layout and 2D/3D road-edges can be drawn. Cut and fill lines along the axis generated in cross-sectionmodule are also drawn. The point coordinates for the axis can be extracted.Some report in a form suitable for use by the surveyor are made.

5. Longitudinal section

This module generates the terrain line at first. The data for generation of theterrain line can be extracted from DEM, using the module LAYOUT, or bysurvey calculations. At the same time a table is created and all relevant data areinserted in it. Vertical tangents can be drawn interactively or by data stored in adatabase. With selection of tangent's line a process for generation of verticalelements starts. Some modification of these elements can be done with theediting tools. The process can be visually controlled by preview option.

Appropriate warnings and messages are displayed promptly when the userinputs incorrect data. When vertical alignment is finished, cross-section slopesand expansions are defined. These calculations are in accordance with thenational standards. The module structure of the program allows differentnational standards to be included very easy. The schemes for horizontal andvertical elements are drawn in the table. At last, road-edges are calculated anddrawn. The data needed for the next steps are stored in the database.



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Figure 4 Longitudinal Section

6. Cross-section

In accordance with the data already created by the other modules, normal cross-section profiles are drawn. Before the process of generation of the normalprofile starts, the terrain line is drawn and a dialogue box appears. In that waythe user can make same corrections in order best suit the profile in the terrain.

Figure 5 Characteristics cross-section

The generation of a normal cross-section is then automaticallyperformed. In accordance with the geomechanical conditions, the maximalheight of embankment or cutting can be limited. When these limitation areexceeded, the customer can interactively construct the body of the railroad. Hecan proceed with the same slope, or, in accordance with the geomechanicalcondition, he can change the slope at appropriate level, or he can put berm atappropriate level. Retaining walls and ditches can be defined and interactivelyinserted in the cross-section profile. Special tools are designed for that purpose.The cutting and fill areas are calculated automatically and saved in a databasefor later calculation of total volumes. Relative cross-section coordinates aretransform into absolute coordinates and are stored for the final layout drawingand 3D representation of the railroad.



7. AutoCAD integration in planning and design process

Current approaches in designing, planning and projecting documentation in theworld are more and more based on Integrated Geographic InformationTechnologies ( document Scanning System, Image Processing System, Rasterand Vector GIS, DBMS, Surface Modeling System). These technologies givegreater efficiency, reduce costs, and give high quality of end products.

The design and planning processes today are conducted independently, withtransfer of information which came too late or even without mutual interchangeof information. This makes difficulties in the function of social and naturalsystems and has an adverse effect on quality of living. In that situation it isnatural to look for integration elements which will harmonise both processes.Then the designer will be able to create projects which will be in accordancewith technical standards but also with ecological, functional and economicrequirement. For example, the phase of creating a general project is almostidentical with the phase of urban planning. For both cases characteristic is theconsideration and estimation of all possible solutions and variants in order tomake the best choice of the corridor, but also to make optimal land use in thecrowded urban areas.

Taking into consideration the fact that AutoCAD and GIS deal with thesame information, maps and resources, it is possible their integration and use inthe form which will be the best suit to the requirement of planners anddesigners. One good example is the combination of drawings created byAutoCAD and maps and databases in GIS, successfully integrated byARC/INFO. At VIII ESRI (Environmental System Research Institute)Conference, 1988, by Dave Flatcher, ARC/INFO was for the first time appliedin the domain of planning and design of traffic roads. That was an indication forextensive investigation to be done in order to make a combination of CAD andGIS which will satisfy everyone's requirement.

AutoCAD database model is organised as a combination of many simplegraphic elements. The basic functions in AutoCAD enable inputting the datamanually, with digitalisation, with the use of graphics tablet, or by makinginterface with the data created by other applications. The entities can be edited,modified, linked with some attribute and displayed in different forms. Analyticalcapabilities of AutoCAD are very poor. On the contrary, GIS's database modelis much complex. Generally GIS creates database which can be used fordifferent applications. GIS has plenty of functions for space calculation, surfacemodeling, control of the spreading of some space phenomena, choosing of theoptimal road and similar. Data can be easily transformed form one to anothergeographical projection.

Comparatively GIS has superior database management system. At thismoment GIS is more efficient but also more expensive system. The main trendin the world investigation is to develop a system which will integrate GISdatabase technology and CAD drawing automation. The leading softwarecorporations, ESRI and Autodesk have made successful integration of both



technologies Their product ArcCAD has all the characteristics of AutoCAD butthe same time at it is a powerful database manager system. It is able to transfergraphical database which is characteristic for AutoCAD in GIS relation databaseformat. ArcCAD can be used as a device which makes ARC/INFO databasetransparent from AutoCAD

With the help of ArcCAD the railway designer can simply transferAutoCAD drawing to his colleague who works on urban planning. Similarly hecan receive information from his planning college about landuse, property,infrastructure and other information stored on the GIS platform.

8. References

1. AutoCAD Reference Manual, AUTODESK, 1992.2. Surface Modeling with TIN, ARC/INFO User's Guide, EnvironmentalSystems Research Institute, 1991.

3.QUICKSURF, Surface modeling inside AutoCAD, SchreiberInstruments, 1994.

4. Microsoft VISUAL C++, Reference Manual, Microsoft Corporation,1994.

5. ArcCAD, Geographic Design System User's Guide, EnvironmentalSystems Research Institute, 1994.

6. VECTOR, User's Manual, Computer Graphics System, 1995.


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