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Using AutoCAD or IntelliCAD for Quantity Surveying
AutoCAD has several command features that enable this. Some of them are not all that obvious or convenient however, and a little guidance on this particular usage is helpful.
Since building details can often be supplied to quantity surveyors in the form of DWG format CAD data, it is very useful for the quantity surveyor to be able to extract measurement data directly from the CAD data, rather than the traditional manual methods of extraction off paper drawings.
For this purpose, AutoCAD LT is entirely adequate. IntelliCAD is a lower cost alternative to AutoCAD that has essentially the same controls and operates with the same DWG file format. The following notes refer to both AutoCAD LT and IntelliCAD. Where there are differences they will be explained. IntelliCAD 98 is directly equivalent to AutoCAD R14 or LT-98. IntelliCAD 2001 is almost the same but can handle DWG files created with AutoCAD 2000 to 2002. AutoCAD LT 2000, 2000i and 2002 has additional features, most of which are not relevant to this topic.
The commands most relevant for making quantities measurements are: LIST, DIST, and AREA.
LIST asks you to select an object or objects on-screen (using AutoCAD’s normal “Select Objects” mechanism), and then displays the properties of those objects in the command prompt area. The properties vary depending on the type of object selected. A CIRCLE object would report something like:
Select objects: 1 found
CIRCLE Layer: “0″
Space: Model space
Handle = 5D
center point, X= 223.7441 Y= 334.1748 Z= 0.0000
DIST prompts you to pick two points and displays the distance between them along the direct line between those points (whether a line actually exists or not), the angle of that line, its 3D angle from the XY plane if the points were in 3D, and the X, Y and Z direction orthogonal vector distances (labelled ‘Delta’) between the two points, thus:
Specify first point: Specify second point:
Distance = 86.6848, Angle in XY Plane = 18, Angle from XY Plane = 0
Delta X = 82.5993, Delta Y = 26.2987, Delta Z = 0.0000
Usually, you would make use of Object Snaps to pick the two points on features of drawing objects.
AREA has more complex variations. It reports the area enclosed by any single enclosing object that you pick such as a circle, ellipse, polygon etc, or by a sequence of connected lines, curves and arcs or Polylines. It also reports an enclosed area for non-closing groups of lines, by inferring the end points being joined by a straight line. In addition, it reports the length of the circumference or perimeter. It does these things regardless of the complexity of the shape, so is very useful for quantities. The AREA command also allows for adding and subtracting measured areas.
The following example measures a closed polyline shape of arcs and line segments, with an internal circle subtracted from its area. Comments have been added in italics.
Specify first corner point or [Object/Add/Subtract]: o (Object option)
Select objects: (Picked a closed Polyline)
Area = 44086.6822, Length = 812.5656
Specify first corner point or [Object/Add/Subtract]: s (Subtract option)
Specify first corner point or [Object/Add]: o (Object option)
(SUBTRACT mode) Select objects: (Picked a Circle within the Polyline)
Area = 3790.4981, Circumference = 218.2494
Total area = -3790.4981
(SUBTRACT mode) Select objects: (enter)
Specify first corner point or [Object/Add]: (enter to finish)
Quite often it may be found useful to draw new lines to enclose areas that need to be measured, if the areas are delineated on the drawing by a rather complex collection of objects, especially if they cross over at corners of the area. The use of the Area command is much easier in such cases if a Polyline is traced over the boundary objects of the area. A Polyline is ideal for this because it is treated as one object and so you can use the Area command’s ‘O’ for Object option. Polylines can comprise straight Line segments and tangential Arc segments. For very free-form curved areas, the Curve object would be a better type to draw. Usually the Quantity Surveyor will be working with a copy of the original drawing file, so it doesn’t matter adding more lines. But even so, it may be best to create a new layer for QS work and draw on that layer. Use a distinctive colour to distinguish the mark-up lines clearer.
All the above commands display their results in the command prompt area. Often, especially with AREA, the text display will mostly vanish as it scrolls in the small prompt area. You can pop up the command text window to see the full extent of the text report. This also allows you to use copy and paste to transfer the report text to some other software, or to collect it in a log file, described below.
AutoCAD 2000 introduced a new mechanism for reporting properties of objects, called the Object Properties window. This is more versatile and powerful and generally easier to use for visual interaction, but does not allow for cutting and pasting or otherwise capturing the report data. Hence it is less useful for Quantities extraction purposes. To use it, display the Object properties window by the Tools menu, Properties. Then select objects so that their Grips appear and the object properties will display in the window. They can also be altered. If more than one object is selected, only properties common to all objects are displayed. If several objects of the same type are selected, it shows all properties, but the ones that vary between objects are blank.
Measurements in mm or metres?
AutoCAD’s dimensions and coordinates are based on arbitrary units called Drawing Units. The user can mentally consider one Drawing Unit to represent any real-world measurement unit. AutoCAD has mechanisms for displaying units in command prompts and dimension text, or accepting user input, in various common unit formats. It names these with terms like Decimal, Engineering, Architectural. In fact, the only one relevant outside USA is Decimal, as the others all refer to American non-metric conventions, such as Feet, inches and fractions of an inch.
When working in metric, there is no setting to define whether Drawing Units are to be considered as millimetres, centimeters, metres or kilometers. In fact, the system always assumes millimetres. You can however, work considering units as metres, and in fact that is the usual practice in Civil Engineering and Survey work with AutoCAD. For architecture and all other disciplines, millimetres are always used in Australia.
Rescaling the drawing to metres
Since Quantity Surveyors often want measurements in metres or square or cubic metres, it is a bit inconvenient to find that the measurement commands such as AREA report values in square millimetres. To obtain results in metres you can re-scale the entire drawing by 1/1000, so that Drawing Units then represent metres. Since a Quantity Surveyor will probably be working on a copy of the original drawing file, changing the drawing in this way should not matter. It may be a good idea to save the re-scaled drawing to a new name, such as by adding ‘-m’ as a suffix.
To rescale the drawing in this way, use the SCALE command. When it asks you to select objects, type ALL and press enter. Then press enter again when the Select objects prompt reappears. It then asks for the origin to use as the re-scale reference point. Enter 0,0,0. Then enter 0.001 when it asks for the scale factor to use. That will most likely make the drawing vanish, as it collapses to 1/1000th of its size. So then type ZOOM E to zoom it to fill the screen with the new drawing Extents. Then it is a good idea to give the REGEN command to ensure circles and curves will display smoothly after the zoom. Then SaveAs to a revised file-name.
This process can be automated by a script or menu macro, which could be added to the Modify menu if you know how to program the menu files. The script used (in the form of a menu macro fragment) is thus:
[Rescale to m]^c^cSCALE all ;0,0,0 0.01 zoom e regen