Abstract:
Embodiments of the present invention include methods for semi-automatic quantity takeoff from computer aided design (CAD) drawings. For each drawing object a corresponding takeoff object is created. A takeoff object may include the dimension of geometry (e.g., numerical, lineal, area) to quantify, the object parameter to be quantified for all instances of the object, and the takeoff calculations to be performed. After a takeoff object is defined, the corresponding instances are automatically identified and quantified. The cost of each instance is then calculated and added to the project cost. Using automated methods, instead of manual techniques, reduces errors and increases the accuracy of the generated cost estimate. Advantageously, the takeoff objects may be saved in the system database and reused for different projects, thereby ensuring consistency between projects. Furthermore, reusing takeoff information, both between instances of an object and between projects, reduces the time required to perform cost estimates.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to computer software. More specifically, the present invention relates to techniques for generating quantity takeoff data from computer aided design drawings. 
     2. Description of the Related Art 
     The term computer aided design (CAD) generally refers to a broad variety of computer-based tools used by architects, engineers, and other construction and design professionals. CAD applications may be used to construct computer models representing virtually any real-world construct. Commonly, CAD applications are used to compose computer models and drawings related to construction projects. For example, a CAD application may be used to compose a three-dimensional (3D) model of a house or an office building. Once composed, these CAD models are often used to generate a variety of two-dimensional (2D) and 3D views such as plan, profile, section, and elevation views. Additionally, such models may be used to generate architectural, construction, engineering, and other documentation related to the construction project. 
     A common requirement of construction projects is to generate an estimate of the cost of the project from the building drawings. This estimate can then be used as part of the bidding process or as part of the pricing process. The term “quantity takeoff” is generally referred to as the process of generating such an estimate. Typically, quantity takeoff involves identifying the quantity of the items associated with the construction project, determining the associated materials and labor costs, and generating an estimate of the cost of the project. Quantities may include numerical counts, such as the number of doors and windows in a project, but may also include other quantities such as the volume of concrete or the lineal feet of wall space. 
     Today, the quantity takeoff process is typically performed manually. For example, a project manager may use a printout, a pen, and a clicker to manually count objects depicted in a set of construction documents. The project manager may physically mark each instance of an object in a CAD drawing, using the clicker to maintain an instance count. A digitizer is often used for taking measurements from the printout. The project manager or cost engineer evaluates each drawing element individually, identifies the material associated with the element, identifies and quantifies the appropriate dimension of the element, calculates the element cost, and adds the element cost to the overall cost estimate. 
     One drawback to this approach is that it has proven to be error-prone. Also, this approach is both labor intensive and time consuming. Moreover, if the project design is modified after the original cost estimate is calculated, the takeoff process may need to be repeated. If the takeoff process is not repeated after design changes, accumulated inaccuracies in the cost estimate may adversely affect the bidding or pricing process. Another drawback to this approach is that it is difficult and expensive to accurately assess the cost impact of different design choices. 
     As the foregoing illustrates, what is needed in the art is a more effective and flexible technique for estimating the cost of a construction project. That is, for more effective and flexible techniques for generating quantity takeoff data. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention include methods for semi-automatic quantity takeoff from computer aided design (CAD) drawings. For each drawing object a corresponding takeoff object is created. A takeoff object may include a dimension (e.g., numerical, lineal, area, or volume) to quantify, the object parameter to be quantified for all instances of the object, and the takeoff calculations to be performed. After a takeoff object is defined, the corresponding instances are automatically identified and quantified. The cost of each instance is then calculated and added to the project cost. Using automated methods, instead of manual techniques, reduces errors and increases the accuracy of the generated cost estimate. Advantageously, the takeoff objects may be saved in the system database and reused for different projects, thereby ensuring consistency between projects. Furthermore, reusing takeoff information, both between instances of an object and between projects, reduces the time required to perform cost estimates. 
     In a first embodiment, the user selects an instance of an object and defines an associated takeoff object. The quantity takeoff engine is configured to use the information in this takeoff object to identify all associated instances in the CAD drawing, quantify these instances, calculate the cost of these instances, and add the quantities and costs to the takeoff report. The user may continue to select objects until all instances in the project have been quantified, thereby generating an estimate for the total project cost. Advantageously, the takeoff measurement tools automatically quantify each instance, thereby increasing the accuracy of the measurements as compared to manual techniques, such as using a digitizer. Moreover, the takeoff calculations, such as labor cost equations, are also performed automatically, further reducing the likelihood of errors in the project cost estimate. 
     In a second embodiment, the information in the CAD drawing is used to create a takeoff tree of undefined takeoff objects and associated instances. Every instance in the CAD drawing is included in the takeoff tree. The quantity takeoff engine evaluates the takeoff tree and prompts the user to define takeoff objects until all of the takeoff objects have been defined. After each takeoff object is defined, the quantity takeoff engine applies the information in the takeoff object to the associated instances in the takeoff tree to generate quantity and cost information for the associated instances. These quantities and costs are added to the takeoff report. Thus, when all takeoff objects have been defined, the takeoff report includes the quantity and cost of each instance in the CAD drawing. In addition to the advantages of the first embodiment, this embodiment also ensures that all instances are quantified. For example, in the first embodiment, it is possible for the user to neglect to select an instance, resulting in an inaccurate project cost estimate. In this second embodiment, the user is prompted if any takeoff objects are undefined, thereby ensuring a complete project cost estimate. 
     In a third embodiment, the quantity takeoff engine is configured to interact with a system database that may contain takeoff objects. The quantity takeoff engine evaluates each instance in the CAD drawing and attempts to map each instance to a corresponding takeoff object in the system database. If there are any instances that are not mapped to a takeoff object, the user is prompted to define additional takeoff objects. The new takeoff objects are added to the system database and the quantity takeoff engine attempts to map the previously unmapped instances to the newly defined takeoff objects. When all instances are successfully mapped, the information in the takeoff objects is used to quantify each instance and subsequently calculate the cost of each instance. These quantities and costs are used to generate a takeoff report for the entire CAD drawing, and thereby a complete estimate of project cost. Advantageously, utilizing the system database in this fashion allows takeoff objects to be shared amongst projects, thereby increasing consistency between projects. Furthermore, as projects are completed, the system database increases in capability. Over time, the creation of new takeoff objects decreases as the system database becomes more complete, thereby reducing the time required to perform takeoff. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  is a conceptual illustration of a computer system in which embodiments of the invention may be implemented; 
         FIG. 2  is a conceptual illustration of elements of the system database of  FIG. 1 , according to one embodiment of the invention; 
         FIG. 3  illustrates an exemplary takeoff object mapping menu, according to one embodiment of the invention; 
         FIG. 4  illustrates an exemplary takeoff object cost data menu, according to one embodiment of the invention; 
         FIG. 5  illustrates an exemplary screen display of the graphical user interface of  FIG. 1 , according to one embodiment of the invention; 
         FIG. 6  illustrates an exemplary takeoff report, according to one embodiment of the invention; 
         FIG. 7  is a conceptual illustration of a 2D CAD drawing sheet, according to one embodiment of the invention; 
         FIG. 8  illustrates a screen display of an exemplary 2D CAD drawing sheet, according to one embodiment of the invention; 
         FIG. 9  is a flow diagram illustrating a method for generating a takeoff report, according to one embodiment of the invention; 
         FIG. 10  is a flow diagram illustrating another method for generating a takeoff report, according to another embodiment of the invention; and 
         FIG. 11  is a flow diagram illustrating another method for generating a takeoff report and further for adding new takeoff objects to the system database, according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a conceptual illustration of a computer system  100  in which embodiments of the invention may be implemented. As shown, the computer system  100  is configured to store takeoff data, perform takeoff measurements, and generate takeoff reports. In one embodiment, the components illustrated in computer system  100  include computer software applications executing on existing computer systems, e.g., desktop computers, server computers, laptop computers, tablet computers, and the like. The software applications described herein, however, are not limited to any particular computing system and may be adapted to take advantage of new computing systems as they become available. 
     Additionally, the components illustrated in computer system  100  may be software applications executing on distributed systems communicating over computer networks including local area networks or large, wide area networks, such as the Internet. For example, a graphical user interface  104  may include a software program executing on a client computer system communicating with a quantity takeoff engine  102 . Also, in one embodiment, the quantity takeoff engine  102  and the graphical user interface  104  may be provided as an application program (or programs) stored on computer readable media such as a CD-ROM, DVD-ROM, flash memory module, or other tangible storage media. 
     As shown, the computer system  100  includes, without limitation, the quantity takeoff engine  102 , the graphical user interface  104 , a keyboard  112 , a mouse  114 , a display device  116 , a system database  106 , a project database  108 , and a CAD drawing  110 . The quantity takeoff engine  102  may be configured to allow users interacting with the graphical user interface  104  via the keyboard  112  and the mouse  114  to generate takeoff objects containing information used to perform the quantity takeoff, such as the unit cost of construction materials, and takeoff reports detailing the estimated cost of the project. Also as shown, the graphical user interface  104  provides takeoff measurement tools  118  and takeoff reporting tools  120 . The takeoff measurement tools  118  may include takeoff object manipulation tools, instance search tools, and takeoff graphical command tools. The takeoff reporting tools  120  may be used to generate and display a takeoff report on the display device  116 . 
     In one embodiment, the system database  106  may include information, such as drawing information and the unit cost of labor, shared among multiple CAD projects. Similarly, the project database  108  may also include drawing information and takeoff calculations, but it may also include project-specific data, such as project cost. 
     The composition of a given design project may be reflected in a collection of one or more CAD drawings  110 . Illustratively, CAD drawing  110  includes a three-dimensional (3D) model  122  and one or more two-dimensional (2D) sheets  124 . The 3D model  122  may represent virtually any real-world construct, for example, a construction plan for a building. In such a case, the 3D model  122  may include detailed 3D geometry representing the building, each floor of the building, and different systems for the building (e.g., electrical systems, HVAC systems, etc.). The 2D sheets  124  may be derived from the 3D model  122  and provide different views of the 3D model  122 , such as plan, profile, and section views of the project. In one embodiment, the quantity takeoff engine  102  may be configured to use and generate information in the system database  106 , the project database  108 , and the CAD drawing  110 . Accordingly, the quantity take off engine  102  and the graphical user interface  104  may include programmed routines or instructions allowing users to create, edit, load, and save elements from system database  106 , the project database  108 , and/or the CAD drawing  110 . In the context of the present invention, for example, the graphical user interface  104  may allow users to create, edit, load, and save takeoff objects and takeoff reports. Those skilled in the art will recognize, however, that the components shown in  FIG. 1  are simplified to highlight aspects of the present invention and that the graphical user interface  104  may include a broad variety of additional tools and features used to compose and manage the system database  106 , the project database  108 , and the CAD drawing  110 . 
       FIG. 2  is a conceptual illustration of elements in the system database  106  of  FIG. 1 , according to one embodiment of the invention. As shown, the system database  106  includes a drawing category  200  and a takeoff category  202 . As described below, the drawing category  200  and the takeoff category  202  are used to organize data within the system database  106 . Those skilled in the art will recognize, however, that the components shown in  FIG. 2  are simplified to highlight aspects of the present invention and that the system database  106  may include a wide variety of organizational structures and data. 
     As shown, the drawing category  200  includes a drawing object 1  204 , a drawing object 2  206 , a drawing object N−1  208 , and a drawing object N  210 . Each of the drawing objects  204 ,  206 ,  208 , and  210  may be created, edited, and used by various CAD tools, including the quantity takeoff engine  102  and the graphical user interface  104  of  FIG. 1 . Furthermore, each of the drawing objects  204 ,  206 ,  208 , and  210  may define an abstract template from which specific instances, or entities, may be created. For example, the drawing object 1  200  may define a toilet object and the CAD drawing  110  of  FIG. 1  may contain numerous instances of toilets, each of which inherits some data from the toilet object designated by drawing object 1  200 . This hierarchy simplifies changes and ensures consistency throughout a construction project. 
     Illustratively, the drawing object 1  200  includes a globally unique identifier (GUID)  220 , linework  222 , and properties  224 . The GUID  220  uniquely identifies the drawing object 1  200  to the quantity takeoff engine  102 , the graphical interface  104 , and any other associated CAD tools in the computer system  100  of  FIG. 1 . That is GUID  220  may be used to represent a common class of drawing objects in CAD drawing  110 . Furthermore, GUID values may be used by other constructs, such as takeoff objects and instances of drawing object 1  200 . The linework  222  may define shapes, such as points, lines, and curves that may be displayed by the graphical user interface  104 . For example, the linework  222  could provide the shapes required to display a toilet in 3D views or in 2D profile, plan, or section views generated from the CAD drawing  110 . The properties  224  may further define how CAD tools interact with the object 1  200  and any instances of object 1  200 . The properties  224  may define metadata about a given drawing object such as width, height, weight, etc. Each of the drawing objects  206 ,  208 , and  210  may include similar information, representing different objects that may be included in the CAD drawing  110 . 
     The takeoff category  202  includes a takeoff object 1  212 , a takeoff object 2  214 , a takeoff object N−1  216 , and a takeoff object N  218 . The takeoff category  202  may correspond to a standard organizational system, such as CSI-16 or Uniformat. Each of the takeoff objects  212 ,  214 ,  216 , and  218  may correspond to a drawing object, such as drawing object 1  200 , and may be created, edited, and used by various CAD tools, including the quantity takeoff engine  102  and the graphical user interface  104 . For example, a takeoff object, such as takeoff object 1  212 , corresponding to a toilet drawing object may be created, added to the takeoff category  202  for plumbing fixtures, and subsequently used for quantity takeoff. 
     As shown, the takeoff object 1  212  includes a drawing object GUID  226 , a quantify type  228 , a quantify property  230 , and cost data  232 . During a quantity takeoff process, the drawing object GUID  226  may be used to identify a particular drawing object and a corresponding set of instances to which the data in takeoff object 1  212  may be applied. The quantify type  228 , the quantify property  230 , and the cost data  232  may then be used to estimate the cost of each of the instances associated with the takeoff object 1  212 . In one embodiment, the quantify type  228  defines the type of enumeration, such as count, linear, or area, that is used to calculate the cost of each instance. And the quantify property  230  may define an instance-specific property, such as a length or a volume, corresponding to the quantify type  228 . In other words, the quantify property  230  defines how the cost of a collection of instances of a given drawing element should be quantified for a takeoff report. The cost data  232  may include numerical constants, such as labor cost per unit, as well as takeoff equations used to estimate cost. 
     For example, the takeoff object 1  212  may be created to correspond to the drawing object of a toilet. In this example, the drawing object GUID  226  of the takeoff object 1  212  may be identical to the object GUID  220  of the drawing object corresponding to the toilet, thereby indicating that the information in the takeoff object 1  212  may be applied to all instances of the drawing object (i.e., instances of the toilet) in a given CAD drawing  110 . In this case, the quantify type  228  may be set to count, indicating that the quantity to measure during takeoff is simply the number of instances of the drawing object corresponding to the toilet. Furthermore, the cost per toilet may be specified in the cost data  232 . The information in takeoff object 1  212 , when applied to the CAD drawing  1110 , allows all instances of the toilet in CAD drawing 1  110  to be counted and the total cost of the toilets to be added to the total cost for the project represented by CAD drawing 1  110 . 
       FIGS. 3 and 4  show an exemplary graphical interface for defining and viewing takeoff object properties. As shown, there are two selectable tabs: cost data and mapping. In  FIG. 3 , the cost data tab is selected and in  FIG. 4  the mapping tab is selected. 
       FIG. 3  illustrates an exemplary takeoff object mapping menu  300 , according to one embodiment of the invention. The takeoff object mapping menu  300  may be configured to allow the user to enter and to view the quantify type  228  and the quantify property  230  of each of the takeoff objects  212 ,  214 ,  216 , and  218  of  FIG. 2 . 
     As shown, the takeoff object mapping menu  300  for a “basic wall” includes a quantify type selection  302  and a quantify property selection  304 . The quantify type selection  302  corresponds to the quantify type  228  of a given takeoff object. In this example, the quantify type  228  may be one of unidentified, linear, area, or count. In the takeoff object mapping menu  300  shown in  FIG. 3 , the quantify property selection  304  is configured to present a list of instance-specific properties. The selected instance property corresponds to the quantify property  230  of a given takeoff object. Illustratively, length is selected, thus, when the quantity takeoff engine  102  performs quantity takeoff on the CAD drawing  110 , the length property of the instances of the drawing object representing a “basic wall” may be the basis of a cost estimate for the instances of a “basic wall” present in the CAD drawing  110 . 
       FIG. 4  illustrates an exemplary takeoff object cost data menu  400 , according to one embodiment of the invention. The takeoff object cost data menu  400  may be configured to allow the user to enter and view the cost data  232  for each of the takeoff objects  212 ,  214 ,  216 , and  218  of  FIG. 2 . 
     As shown, the takeoff object cost data menu  400  includes a unit and labor cost selection  402  and an equipment cost selection  404 . In one embodiment, the unit and labor cost selection  402  may be configured to allow the user to view and specify items relating to the costs of material and labor, such as the currency, unit, material cost per unit, and labor cost per unit. Similarly, the equipment cost selection  404  allows the user to view and specify the cost of any associated equipment using the currency specified in the unit and labor cost menu  402 . 
     Illustratively, in this example, cost data is shown for a takeoff object of “basic wall”. As shown, the base quantity to be measured is length, the currency is dollars, the material cost per unit of length is $20, the labor cost per unit of length is $14, and the equipment cost is $0. 
       FIG. 5  illustrates an exemplary screen display of the graphical user interface  104  of  FIG. 1 , according to one embodiment of the invention. More specifically, the screen display in  FIG. 5  illustrates a takeoff list  500 . As shown, the takeoff list  500  includes takeoff categories, such as the takeoff category  202  of  FIG. 2 ; takeoff objects, such as takeoff object 2  04  of  FIG. 2 ; and the instances in the CAD drawing  110  of  FIG. 1  that are associated with each of the takeoff objects. The takeoff list  500  facilitates user-interaction with the takeoff measurement tools  118  of  FIG. 1 , the takeoff reporting tools  120  of  FIG. 1 , and the quantity takeoff engine  102  of  FIG. 1 . 
     Illustratively, in this example takeoff is being performed on a specific instance of the takeoff object for a “basic wall”. Alternatively, as also shown in the menu options in this example, the user may execute “select all instances” before executing takeoff and, thereby, perform takeoff on all instances of a “basic wall” simultaneously. 
       FIG. 6  illustrates an exemplary takeoff report  600 , according to one embodiment of the invention. Using the takeoff reporting tools  120  of  FIG. 1 , the takeoff report  600  may be configured to display the takeoff data in a variety of forms. As shown, the takeoff report  600  is configured to include a description  602 , a quantity  604 , a material cost  606 , a labor cost  608 , an equipment cost  610 , and a total cost  612 . 
     Also as shown, the column under description  602  includes takeoff objects and associated instances. For each item shown under the description  602  heading, the quantity  602 , the material cost  604 , the labor cost  608 , the equipment cost  610 , and the total cost  612  is displayed. Furthermore, the material cost  610  is configured to show both the cost per unit of the material and the total cost of the material. Similarly, the labor cost  608  is configured to show both the unit cost of labor and the total cost of labor. 
     In the specific takeoff report  600  illustrated in  FIG. 6 , the description column indicates that the quantity takeoff engine  102  has performed takeoff on the “basic wall” and the “door #1” takeoff objects. Furthermore, the description column shows that the quantity take off engine  102  has identified four instances corresponding to the “basic wall” takeoff object and one instance corresponding to the “door #1” takeoff object. As can be seen in the square corresponding to the quantity column of the “basic wall” row, the total quantity used to calculate the cost of the four instances of the “basic wall” is 18.97 meters. Similarly, the total quantity used to calculate the cost of the one instance of “door #1” is 1 each. The total cost column shows a total cost of $569.10 for the four instances of “basic wall”, a total cost of $48.00 for the one instance of “door #1”, and a cumulative project total cost of $617.10. 
       FIG. 7  illustrates an example of one of the 2D sheets  124  of  FIG. 1 , according to one embodiment of the invention. As shown, the 2D sheet  124  includes an instance 1  700  of a drawing object, an instance 2  702  of a drawing object, an instance N−1  704  of a drawing object, and an instance N  706  of a drawing object. Each of the instances  700 ,  702 ,  704 , and  706  correspond to a drawing object, such as drawing object 1  204  of  FIG. 2 . Each drawing object may be defined in the system database  106  of  FIG. 1 , the project database  108  of  FIG. 1 , or the CAD drawing  110  of  FIG. 1 . 
     The instance 1  700  is configured to include a drawing object GUID  708 , a position  710 , an instance GUID  712 , and properties  714 . The instance 1  700  may inherit data from the drawing object designated by the drawing object GUID  708 . For example, if the drawing object corresponding to the drawing object GUID  708  defines a door, instance 1  700  will inherit the linework  222  and the properties  224  that define this door. The position  710  specifies the location of the instance 1  700  relative to other instances, such as the instance N  706 , included in the CAD drawing  110 . For example, the position  710  may specify a 3D coordinate location within a space represented by the 2D sheet  124 . The instance GUID  712  uniquely identifies the instance 1  700  to the quantity takeoff engine  102 , the graphical interface  104 , and any other associated CAD tools in the computer system  100  of  FIG. 1 . While instance 1  700  and instance 2  702  may share the same drawing object GUID  708 , thereby indicating that they are both instances of the same drawing object, instance 1  700  and instance 2  702  have different instance GUIDs  712 . The properties  714  include information that is specific to each instance, as opposed to information that is shared between instances of the same object. For example, one of the properties  714  such as length or width may be used as the basis for quantifying the instance 1  700  during a quantity takeoff process. Each of the instances  702 ,  705 , and  706  may include similar information. 
       FIG. 8  illustrates a screen display of an exemplary 2D sheet of  FIG. 1  according to one embodiment of the invention. As shown, the screen display includes a visual representation of the instance 1  700  of  FIG. 7 . In this example, the appearance of the instance 1  700  indicates that it is a door. The graphical user interface  104  of  FIG. 1  may be configured to allow the user to interact with the visual representation of the CAD drawing  110  of  FIG. 1  and, thus, the instances contained within the CAD drawing  110 . 
       FIG. 9  is a flow diagram of a method  900  for generating the takeoff report  600  of  FIG. 6 , according to one embodiment of the invention. Although the method  900  is described in conjunction with the systems of  FIGS. 1-8 , persons skilled in the art will understand that any system that performs the steps of the method  900 , in any order, is within the scope of the invention. 
     As shown, the method  900  begins at step  902 , where the user invokes the quantity takeoff engine  102  and loads the CAD drawing  110 . In step  904 , the user selects an instance of a drawing object from the CAD drawing  110 . In step  906 , a new takeoff object is created to represent takeoff data for the drawing object selected in step  904 . In one embodiment, the new takeoff object may include the drawing object GUID  226 . The GUID  226  may be copied from the particular instance of a drawing object GUID  708  selected at step  904 , thereby creating the association between the takeoff object and the drawing object, based on the instance of a drawing object by the user. 
     In step  908 , the takeoff object mapping menu  300  is displayed and the user may enter values for the quantify type  228  and the quantify property  230 . In step  910 , the takeoff object cost data menu  400  is displayed and the user may enter takeoff cost information, such as the cost data  232 . In step  912 , the quantity takeoff engine  102  may parse the CAD drawing  110  to identify all drawing objects in which the drawing object GUID  708  matches the drawing object GUID  226  of the takeoff object defined in steps  906 - 910 . In other words, the quantity takeoff engine  102  may identify all objects in the CAD drawing  110  of a common type, as represented by object GUID  708 . 
     In step  914 , the takeoff measurement tools  118  and the quantity takeoff engine  102  may use the quantify type  228  and the quantify property  230  to quantify each of the instances identified at step  912 . In one embodiment, each such instance may be marked as being part of a common takeoff group. That is, the quantity takeoff engine  102  may determine the appropriate takeoff quantities for the collection of drawing object instances identified at step  912 . For example, for a door object, the quantity may be a simple count of the number of instances of the door object in the drawing. Of course, more complicated takeoff calculations may be performed. For example, for a wall object, the takeoff engine  102  may evaluate instances of the wall object in CAD drawing  110  to determine a combined linear length of all such walls. 
     In step  916 , the quantities determined at step  914  are used in conjunction with the cost data  232  to estimate the cost of the identified instances. For example, for a simple numerical count quantity takeoff calculation, the number of identified instances may simply be multiplied by the unit cost for the material and labor, as specified in the takeoff object, to determine the total cost of the instances. In step  918 , the takeoff reporting tools  120  may add the quantities measured in step  914  and the costs calculated in step  916  to the takeoff report  600 . At step  920 , the user may select another instance in a CAD drawing to be the basis of another takeoff object. In such a case, the method  900  returns to step  906 , where a new takeoff object is created. The user may continue in this manner to create as many new takeoff objects as desired. 
     The method  900  may be useful where a user desires to incrementally build a takeoff report by iteratively selecting the linework for an instance of each drawing object. However selecting linework may become tedious and the user may desire to use a more structured selection method. Accordingly, in one embodiment, the quantity takeoff engine  102  may be configured to identify a collection of drawing objects in the CAD drawing  110  and to generate corresponding takeoff objects for each identified drawing object. 
       FIG. 10  is a flow diagram illustrating a method  1000  steps for generating the takeoff report  600  of  FIG. 6 , according to one embodiment of the invention. Method  1000  uses information from the CAD drawing  110  of  FIG. 1  to automate more of the takeoff process. Although method  1000  is described in conjunction with the systems of  FIGS. 1-8 , persons skilled in the art will understand that any system that performs the method  1000 , in any order, is within the scope of the invention. 
     As shown, the method  1000  begins at step  1002 , where the user invokes the quantity takeoff engine  102  and loads the CAD drawing  110 . In step  1004 , the quantity takeoff engine  102  may generate a model tree of drawing objects and instances from the CAD drawing  110 . The model tree stores drawing objects and instances of drawing objects. In one embodiment, instances of a drawing object in the CAD drawing  110  that share a common drawing object GUID  708  may be grouped together in the model tree. In step  1006 , a takeoff object is created for each distinct drawing object in the model tree. In one embodiment, each takeoff object includes the drawing object GUID  226 . Advantageously, the groupings in the model tree are preserved, thus each takeoff object may also include a reference to each instance of a drawing object that corresponds to the drawing object GUID  226 . In step  1008 , the model tree is used to populate the takeoff list  500  with the takeoff objects and their associated instances. For example,  FIG. 5  illustrates an example of a takeoff list  500  that may be displayed using the graphical user interface  104 . 
     In step  1010 , the user may specify properties for a takeoff object for one of the entries in the takeoff list. Accordingly, in step  1012 , the takeoff object mapping menu  300  is displayed and the user enters the quantify type  228  and the quantify property  230  for a given takeoff object. In step  1014 , the takeoff object cost data menu  400  is displayed allowing the user to enter takeoff cost information, such as the cost data  232 . 
     In step  1016 , the takeoff measurement tools  118  and the quantity takeoff engine  102  use the quantify type  228  and the quantify property  230  to quantify each of the instances associated with the selected takeoff object. That is, at step  1016 , the instances of the drawing object associated with the selected takeoff object are evaluated to generate the appropriate takeoff quantities for a set of instances in the CAD drawing  110 . In step  1018 , the quantity takeoff engine  102  evaluates these quantities along with the cost data  232  to estimate the cost for each of the instances of the drawing object in the CAD drawing  110 . In step  1020 , the takeoff reporting tools  120  may add the quantities measured in step  1016  and the costs calculated in step  1018  to the takeoff report  600 . At step  1022 , the quantity takeoff engine  102  analyzes the takeoff tree to determine if the cost estimate is complete. If there are additional instances of drawing objects that have not been quantified, the method returns to step  1010 , where the user defines another takeoff object from the takeoff object list. The method  1000  continues in this fashion until each takeoff object in the takeoff tree has been defined and processed, thereby generating the takeoff report  600  and, thus, a cost estimate representing the entire project. 
     The method  1000  may be useful where a user desires to incrementally build a takeoff report. However a user may prefer to generate a complete takeoff report using a single command. Furthermore, a user may wish to share takeoff objects between construction projects. 
       FIG. 11  is a flow diagram of method steps for generating the takeoff report  600  of  FIG. 6  and adding new takeoff objects to the system database  106  of  FIG. 1 , according to one embodiment of the invention. Storing takeoff objects in the system database  106  allows takeoff objects to be shared among multiple projects, thereby increasing takeoff consistency between the projects. For example, an architectural firm may wish to reuse takeoff objects defined for elements of a given CAD drawing across multiple drawing projects. Doing so avoids having to recreate this data from scratch each time. In one embodiment, the system database may be used to store take off objects used for reuse in multiple design projects. Although the method steps are described in conjunction with the systems of  FIGS. 1-8 , persons skilled in the art will understand that any system that performs the method steps, in any order, is within the scope of the invention. 
     As shown, the method  1100  begins at step  1102 , where the user invokes the quantity take off engine  102 , loads the CAD drawing  110 , and loads the system database  106 . In step  1104 , the quality takeoff engine  102  attempts to map instances of drawing objects in the CAD drawing  110  to the takeoff objects defined in the system database  106 . For example, the quantity takeoff engine  102  may be configured to match the drawing object GUID  708  for a given instance to the drawing object GUID  226  of the takeoff objects. At step  1106 , the CAD drawing  110  is analyzed to determine if all the instances have been mapped to takeoff objects. If all the instances have been mapped, the method  1100  skips steps  1108 - 1110  and continues at step  1112 , where the instances are quantified, according to the matching takeoff object associated with a given instance of a drawing object. 
     In step  1108 , the quantity takeoff engine may be configured to prompt the user to define additional takeoff objects for instances of drawing objects that were not matched to a takeoff object at step  1104 . For example, in one embodiment, new takeoff objects may be defined according to steps  904 - 910  of the method  900  illustrated in  FIG. 9 . In step  1110 , the system database  106  is updated with the takeoff objects created in step  1108 . The method  1100  then returns to step  1104 , where all instances of drawing objects in the CAD drawing  110  are mapped to takeoff objects defined in the system database  106 . As persons skilled in the art will recognize, step  1104  may be performed in an incremental fashion, such that only unmapped instances and new takeoff objects are considered during the mapping process. Again, at step  1106 , if all instances of drawing objects are mapped to takeoff objects, the flow continues at step  1112 . Otherwise, method  1100  may continue to loop through steps  1108 ,  1110 ,  1104 , and  1106  until all instances of drawing objects in a given CAD drawing are mapped to takeoff objects. 
     In step  1112 , the takeoff measurement tools  118  and the quantity takeoff engine  102  use the quantify type  228  and the quantify property  230  to quantify each of the instances of drawing objects in CAD drawing  110 . In step  1114 , the quantity takeoff engine  102  evaluates these quantities along with the cost data  232  to estimate the cost for each instance of each drawing object in the CAD drawing. In step  1116 , the takeoff reporting tools  120  generate the takeoff report  600  from the quantities measured in step  1112  and the costs calculated in step  1114 . The takeoff report  600  generated in this flow includes the total estimated cost of the project defined in the CAD drawing  110 . 
     In sum, the data contained in CAD drawings may be used to automate portions of the takeoff process used to generate estimated costs for a construction project. Typically, a CAD drawing contains abstract drawing objects from which concrete instances may be derived. Each instance may include instance-specific information that may be supplemented with information inherited from the associated abstract drawing object. This hierarchical approach simplifies the CAD drawing. In a similar fashion, much of the information required to perform takeoff calculations, such as material cost, may be consolidated into abstract takeoff objects. Typically, data in the takeoff object may include a mapping method, such as using an object GUID, to identify instances of a drawing object associated with the takeoff object; the quantify type, such as count, linear, or area; the instance-specific property, such as length or volume, to be quantified; and takeoff cost information, such as material cost per unit of the quantify property. The quantity takeoff engine and the graphical user interface may be configured to interact with these takeoff objects to automate some of the steps in takeoff process. Advantageously, consolidating takeoff information and automating steps in the takeoff process reduce both the likelihood of errors and the time required to perform quantity takeoff. Furthermore, reducing the time required to perform quantity takeoff facilitates quickly and accurately assessing the cost impact of different design choices. 
     In a first embodiment, the user selects an instance and defines an associated takeoff object. The quantity takeoff engine is configured to use the information in this takeoff object to identify all associated instances in the CAD drawing, quantify these instances, calculate the cost of these instances, and add the quantities and costs to the takeoff report. The user may continue to select instances until all instances in the project have been quantified, thereby generating an estimate for the total project cost. Advantageously, the takeoff measurement tools automatically quantify each instance, thereby increasing the accuracy of the measurements as compared to manual techniques, such as using a digitizer. Moreover, the takeoff calculations, such as labor cost equations, are also performed automatically, further reducing the likelihood of errors in the project cost estimate. 
     In a second embodiment, the information in the CAD drawing is used to create a takeoff tree of undefined takeoff objects and associated instances. Every instance in the CAD drawing is included in the takeoff tree. The quantity takeoff engine evaluates the takeoff tree and prompts the user to define takeoff objects until all of the takeoff objects have been defined. After each takeoff object is defined, the quantity takeoff engine applies the information in the takeoff object to the associated instances in the takeoff tree to generate quantity and cost information for the associated instances. These quantities and costs are added to the takeoff report. Thus, when all takeoff objects have been defined, the takeoff report includes the quantity and cost of each instance in the CAD drawing. In addition to the advantages of the first embodiment, this embodiment also ensures that all instances are quantified. For example, in the first embodiment, it is possible for the user to neglect to select an instance, resulting in an inaccurate project cost estimate. In this embodiment, the user is prompted if any takeoff objects are undefined, thereby ensuring a complete project cost estimate. 
     In a third embodiment, the quantity takeoff engine is configured to interact with a system database that may contain takeoff objects. The quantity takeoff engine evaluates each instance in the CAD drawing and attempts to map each instance to a corresponding takeoff object in the system database. If there are any instances that are not mapped to a takeoff object, the user is prompted to define additional takeoff objects. The new takeoff objects are added to the system database and the quantity takeoff engine attempts to map the previously unmapped instances to the newly defined takeoff objects. When all instances are successfully mapped, the information in the takeoff objects is used to quantify each instance and subsequently calculate the cost of each instance. These quantities and costs are used to generate a takeoff report for the entire CAD drawing, and thereby a complete estimate of project cost. Advantageously, utilizing the system database in this fashion allows takeoff objects to be shared amongst projects, thereby increasing consistency between projects. Furthermore, as projects are completed, the system database increases in capability. Over time, the creation of new takeoff objects decreases as the system database becomes more complete, thereby reducing the time required to perform takeoff. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.