Preparing an AutoCAD drawing for 3D

by Ian Ibbotson

Introduction

It is extremely important to prepare an AutoCAD drawing taking into consideration two main issues

1. The drawing should be organised and drawn so as not to compromise the production drawing. This means that it should be drawn in a manner that benefits both the AutoCAD outputs and the 3D outputs. Correct layering, closed polylines created from a framework and simplified object positioning are examples of this process
2. The drawing should be organised to facilitate easy import / export with MAX/VIZ. Keeping a handle on what elements will need to be created as single objects in 3D and which will need to be created as one object is very important. Also, making the layer system easily understandable and 'object focussed' is important

This tutorial explains the main issues to consider when drawing in AutoCAD and preparing a drawing for use in 3D work

Download Sample Data

kf301_files.zip (583kb)

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Layers and Drawing Methods

Organisation of all elements that are to be used in 3D using layers is vital as well as a good knowledge of clean, accurate drawing methods for 3D work. Remember that what looks acceptable in 2D may not work as you want in 3D and may look terrible. A good example of bad drawing is the non-use of arcs in the polyline command where a curved road section is represented by a series of line segments. When turned into a kerb line in 3D it will look like the image below:

The correct drawing method (which is easier) produces a good looking and accurate result in 3D

Clean and Simplify Drawing

Before using an AutoCAD drawing for importing into MAX/VIZ only those elements that are going to be used for 3D work need keeping in the drawing. Extraneous lines and text should be removed and a 'buffer' drawing used instead of a main production drawing. The following checklist should also be implemented before starting to use AutoCAD data:

• Purge the drawing of all items and nested items
• Audit the drawing
• Set UCS to World if another has been used
• Bind Xrefs
• Detach Images
• Use Drawing Cleanup tools if using Autodesk Map to simplify linear features and remove duplicates etc

• Finally, display just those elements that are going to be used and Copy and Paste into a New Drawing. Use Edit > Copy then Edit > Paste to Original Coordinates

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Layers

The main method of creating objects in MAX/VIZ outlined in these tutorials is to create objects from layers. This is a straight forward process that allows you to think 'objects' right from the start

Open kf301_01.dwg in AutoCAD. This drawing contains an example layer system used for easy import to MAX/VIZ

NOTE: Creating separate objects from one layer in MAX/VIZ is handled on the import options dialogs in MAX/VIZ

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Drawing Methods

Good clean drawing techniques are essential to produce good looking scenes and benefit the drawing as a whole. Together with a comprehensive layer system based on 'objects' and the use of closed boundaries using a framework layer, and the boundary command, the use of appropriate AutoCAD tools make transition into 3D much easier. This tutorial explores some of the basic useful commands to create clean, simple, accurate lines in AutoCAD

NOTE: The creation of closed boundary polygons and comprehensive layer system is useful for other outputs from AutoCAD and 3rd party applications. Export to CorelDraw or Mcolour for plan graphics, hatching areas in AutoCAD and listing of area quantities are good examples of extended functionality using these methods

TIP: Always draw lines using the Polyline command. Using the Line command produces fragmented and less managable drawings

• Open kf301_02.dwg. This drawing contains some layers for a creating surfaces and a kerb for a simple landscape scheme (shown completed below)

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Building

Notice that a layer called 'Framework' has been created and there are building framework lines already drawn. These have been created using the Offset command. The landscape drawing is constructed by referencing the known positions of points and lines of the building - as it would be constructed on-site

• Make Building layer current
• Draw > Boundary > Pick Points - pick a point in the middle of the building framework lines. This creates a closed boundary for the building on the correct layer

NOTE: If the Boundary command does not work check the following points:

1. Elements such as blocks are frozen and not turned off (AutoCAD still includes off layers when searching for a boundary)
2. The boundary extents can be viewed on the screen (only graphics on the present screen display are included in the boundary search)
3. All existing polylines and framework lines are 2D at zero height (ie not 3D polylines)
4. There are no gaps in any of the polylines

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Car Park

• Make Framework layer current
• Draw a framework polyline from the bottom right corner of the building vertically up using Ortho On (F8 toggles Ortho on>off)
• Offset this line 30 metres to the right
• Turn OSnap On (Object Snap) and change the Snap Settings to Endpoint. Draw a horizontal polyline from the top right corner of the  building horizontally using Ortho On so that it crosses the previously drawn polyline
• Draw a ciclcle snapped to where these lines meet with a radius of 5 metres (this value can be typed on the command line when creating the circle)
• Start drawing a framework polyline snapped from the top right corner of the building with the second vertex of the polyline snapped (intersection snap) to where the circle crosses the line. Then type A at the command line (this is a polyline sub-command - look at the command line - which allows you to draw an arc as part of a polyline). Snap the next vertex to where the circle crosses the vertical framework line. Then type L at the command line (this takes you back to drawing a normal line within the polyline). Using Ortho On drag the polyline down and complete the polyline as shown below. This process accurately offsets the car park edge and gives a rounded corner of radius 5 metres

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First Path and Road

• Delete the circle
• Extend the bottom horizontal building framework line to meet the new car park edge framework line and Offset the new car park edge line left 5 metres to the left. This creates a framework line for the road
• Offset the extended framework line down 2 metres and the original right hand vertical framework building line to the right 2 metres. This creates framework lines for the first path
• Trim the lines and Delete unecessary lines so the framework looks like the image below. Using Ortho On draw a framework polyline that closes the road at the lower end

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Grassed Area and Planting Beds

• Using Grips with Ortho On drag the left building framework line down and the line created to close the road across left so they cross
• Using Ortho On draw a polyline line starting from the corner of the path down and using the Arc sub polyline command then Line sub polyline command describe the large planting bed

NOTE: Arc sub commands must only be used after starting to draw a polyline in Line mode. Otherwise the arc 'balloons' due to it not having any direction

• In the left corner of the grassed area framework create a circle snapped to the edge corner of the path framework to describe the small planting bed

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Second Path

• Draw a polyline using the Arc sub command and Line sub command to describe the centre line of the second path
• Offset this line 0.75 metres to the left and 0.75 metres to the right
• Delete the centre polyline to give an initial framework for the second path

• To splay the entrance points to the path Trim both ends of the path:

• Finally (to complete the framework) Fillet the corners or the path entrances. Before filleting, Join the framework polylines using Pedit then use the Fillet command to create a fillet of radius 2 metres at each corner. Then use Snaps to snap a polyline to close the path ends
• Trim the circle for the small planting bed so the lines do not interfere with the creation of boundaries

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Create Surface Boundaries

Making each layer current in turn use the Boundary command to quickly create boundaries for each element
Turn the Framework layer off

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Create Kerb Line

• Offset the Car Park boundary by 0.15 metres
• Select the offset polyline and place on the Kerb layer by selecting the Kerb Layer in the Layer Dropdown List and then pressing Esc twice. This layer will be turned off before importing into MAX/VIZ as edges are created from the boundary lines using the Loft compound object

This small tutorial shows how simple the geometry should be when importing to MAX/VIZ. The drawing should contain no edge information apart from the closed boundaries that delineate all surfaces seamlessly (the subject of this tutorial). Secondly, objects such as trees, benches, lamp posts etc should be represented by simple circle and rectangular blocks on the correct layers. These simple 2D blocks are replaced in MAX/VIZ with 3D objects, but are positioned in AutoCAD. Thirdly, 3D landform information in the form of contours, 3D polylines (strings) or a triangulated mesh is needed in order to transform the 2D plan into a 3D scene

NOTE: This sequence of tutorial files has been saved as four drawings: kf301_02a/b/c/d.dwg for reference

Checklist of Commands

Become very familiar with the following commands which were all used to quickly and accurately create this simple landscape plan. More complicated plans simply repeat these commands over and over again

Move
Rotate
Copy and Multiple Copy
Offset
Trim
Extend
Boundary
Fillet > Chamfer
Pedit
Manipulation of Vertex Handles
Snap Mode On>Off and Snap Settings
Ortho

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Simplify Blocks

Complicated 2D blocks should not be imported into MAX/VIZ if they are merely used as markers for 3D Objects or as objects for replacing with 3D objects. Replacing blocks with much simpler blocks before importing into MAX/VIZ is straightforward in AutoCAD using the Reference Edit dialog

• Open kf301_03.dwg. This drawing contains four detailed graphic blocks for trees which need simplifying by replacing them with circles

• Select one of the blocks (they are all the same block reference) and double left click. This opens the Reference Edit dialog

NOTE: The Reference Edit dialog is a feature of AutoCAD 2004 plus. Replacing blocks in previous versions of AutoCAD entails 'redefining blocks'

• Press Ok to isolate the block and open it up for editing. A small toolbar appears and only the block is available for editing. All other blocks of the same name disappear and all other elements in the drawing turn grey
• Zoom to the block and draw a circle in the same position and at the same size as the tree block

 

• Draw a circle around the tree block on layer 0, then delete the tree block lines
• Press the Save back changes to reference button to replace all references of the block with a simple circle

TIP: Another option for replacing blocks can be found on the Express Menu/Blocks. Use Replace block with another block to quickly replace a block in the drawing with another

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Import Options

Before importing data from AutoCAD into MAX/VIZ two issues must be addressed

1. If the drawing has been created far from 0,0 on the X and Y axes, the drawing data needs to be moved closer to 0,0. This improves how MAX/VIZ handles the data in the later stages and makes sure the modelling is accurate and any animation smooth
2. The relationship between the layers and how they are configured to create objects on import needs to be understood. Then simple routines using one of two separate import dialogs can be used to update the MAX/VIZ scene at any time

This section explains how to separate drawing data for MAX/VIZ from the production design drawings and how to configure the Import dialog for easy update of the scene from AutoCAD

NOTE: If drawing units are in millimeters, then also re-scale the drawing at this stage (it is not advisable to keep in millimeters for a landscape scale project)

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Move to Zero

If AutoCAD geometry is created far from zero, then accuracy problems may occur when modelling this data in MAX/VIZ. This is due to the fact that AutoCAD is accurate to 64 decimal places, whereas MAX/VIZ is only (only?) accurate to 32 decimal places. The problem usually manifests itself when animating cameras along paths when 'camera shake' will occur. Large bounding boxes around objects are also a problem if the AutoCAD data is far from zero because the bounding boxes start at 0,0

AutoCAD drawings created far from zero are usually the result of using Ordnance Survey basemap information to start the drawing process. Most basemap tiles are hundreds of thousands of metres away from zero on the X and Y plane. Needless to say, landscape drawings are often created far from zero

• Either move the basemaps to zero before creating the drawing and in the knowledge that other data need not be added in a 'mapped' environment or use a separate drawing for 3D work with a known basepoint for moving geometry to zero thus:

• Open and manage a new separate drawing for importing into MAX/VIZ
• Import the following three elements needed for visualisation work into this new drawing: Closed boundary lines delineating all surfaces / Simple blocks for objects / Landform data in the form of Contours, 3D polylines (strings) or Triangulated Mesh or Grid

TIP: Use Autodesk Map 3D to attach the project design drawing to the MAX/VIZ drawing and use simple layer property queries to add elements to the MAX/VIZ drawing at any time. This is a very effective method of filtering just the data needed for 3D work whilst keeping separate from the production drawings. It allows the original design drawing to be changed without having to worry about layers on>off and layers that are not relevant to 3D work (drawing for 3D work should be very straight forward and almost simplistic). Complicated blocks for trees, seats, lamp posts etc can even be replaced with simple blocks as part of the process. Changing 2D plans using GIS functionality and visualising these scenarios in 3D is another advantage of using Autodesk Map 3D with MAX/VIZ

• Open kf301_04.dwg. This drawing is an example of a drawing containing these three elements. However, if you look at the coordinates of the data on the Satus Bar you will notice that it is far from zero

Round these coordinates up to 320000,456000

• Zoom out and record on a peice of paper the rounded up coordinates preferably to the bottom left of the site. The rounded up coordinates would be 320000, 456000 in this case. This happens to be in the centre of the scheme, but this is Ok
• Turn on and unfreeze all layers
• Select all the elements in the drawing and use the Move command to move the data to zero thus:
• When prompted for the base point or displacement type 320000,456000 on the command line then Return
• When prompted for the second point of displacement type 0,0 on the command line then Return. This moves the data from a known recorded point to 0,0

TIP: Another method involves drawing a rectangle around the site (on a layer that can be frozen) and using the bottom left corner of the rectangle as the move base point

The drawing is now ready for import into MAX/VIZ without any problems connected to being sited far from zero. Repeat this routine to move any new data from the original 2D design drawing

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Import AutoCAD Drawing Dialogs

To control how AutoCAD data is imported into MAX/VIZ one of two Import Drawing dialogs is used depending on how the data has been organised in AutoCAD and how the objects need to be organised in MAX/VIZ

Importing using the Legacy AutoCAD dialog

This dialog is the 'old' version but does have some useful features

1. You can import text
2. Objects are named the same as the layer they were created on in AutoCAD to help with object organisation

• Reset MAX/VIZ
• File > Import. On the Select File to Import dialog change the Files of Type to Legacy AutoCAD (*DWG). Select kf301_05.dwg then Open
• On the Dwg Import dialog select Merge and press Ok

• On the Import AutoCAD Dwg File dialog check the following:

• Press Ok

• In the Select by Name dialog note that all the layers have been turned into objects and that all the steps, for instance, are one object. This is Ok for some objects, but not others. It is handy for the contours to be imported like this. So too the positioning blocks for landscape objects such as bollards, seating and lamp posts. However, objects such as the steps need to be imported as separate objects. To import those objects that have been imported incorrectly delete the objects and re-import having changed the import settings as follows:

• Delete Steps bottom.01, Steps top.01, Sundial.01 and Wall.01

Importing using the AutoCAD Drawing dialog

This dialog is the most recent version and has other useful features

1. You can select objects on layers you want to import from a layer list
2. Objects, however, are not renamed but organised in layers in MAX/VIZ

• File > Import. On the Select File to Import dialog change the Files of Type to AutoCAD Drawing (*.DWG,*.DXF). Select kf301_05.dwg then Open
• On The Layers Tab choose Select from list and select the following layers:

• On the Geometry Tab select the following options:

• Press Ok to import the objects into MAX/VIZ
• Notice that the all objects have been named 'polyline' ie as the object 'type'. Use the Layer dialog and Rename dialog to organise the objects further:
• Open the Layer dialog and right click over Steps bottom. Choose Select from the right click menu. This selects all the bottom step boundary lines

TIP: If the Layer dialog is not displaying right click on the main toolbar (not on an icon) and select Layers from the list

• Tools > Rename Objects. On the Rename dialog type in the Base Name, check 'Numbered' and set the Base Number to 1

• Press Rename to rename all the objects selected

All objects are now in the correct format and named correctly in order to make the modelling process easier

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