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C A R T - Computer Aided Recording Tool

Cover Image (155k)

Automating the Drafting for As-Found Recording and Facility Management

Introduction

Much of the time of a facility planner, restoration architect or heritage recorder is spent, on site analysing the structures and collecting data and measurements which will be used later to create the reports and drawings that will provide the basis for the subsequent design. However this is just the beginning of the long process of drafting the as-found situation. Errors are inevitable in this type of work but, typically they only come to light back in the office where confirming a measurement may entail an extra trip to the site and, even worse, there are times they only turn up when a contractor encounters problems on the job.

Recently, major changes have taken place in the way ideas are being put on paper. Word processors, spread sheets, databases and Computer Aided Drafting (CAD) are all common tools of the profession but the initial record is still being collected primarily on paper. There have been some attempts to systematize the collection of data with a view to facilitating its input into the CAD system including hand measurements (O'Brien 1994) (Partridge 1994) and some imaginative work automating photogrammetry (Streilein 1994) but the fundamental problem is that tools intended for design are not well suited to recording.

At the level of system analysis, it is not surprising that a different tool would be required for the description of an idea than for the description of an object. In CAD, for instance, assumptions about right angles, parallel walls and horizontal floors, all appropriate to design, are counter productive when applied to recording. Clearly some new tools are required, tools that will respect the requirements of that discipline but still prepare the CAD models and the knowledge base around which the subsequent design will be structured.

Is it possible to take as input the measurements and notes collected on-site and from them create a CAD model ready for the architects or facility managers to use? This paper will describe a working prototype of such a tool.

The idea for CART did not come from analysing the problem and coming up with requirements for a new program but rather, as is often the case, by the existence of some work that needed to be done. These first projects, "Mclean Mill"(1) and "Humeima"(2) were not even the facility surveys or as-found drawings that we expect will make the most use of this software in the future but rather archaeological excavations.

Archaeology is concerned with exactly how the various components lie, down to the individual brick or stone, and with detailed observations about each object. In fact this is no different, except in degree, than the interest of the architect in the geometry of a structure or of a facility manager in wanting to know the details concerning the objects being tracked.

Data Collection

image (12k) The first step, of course is data collection. Traditionally a rough sketch was made of the building and then a team with tape measures would dimension the sketch and a good recording team would also be making notes about conditions, materials, colours and the like. When everything was measured the recorders would move to the drafting board or computer and render these notes into measured drawings.

Object Naming

With the CART system the structure becomes a list of objects, walls, doors, outlets, or whatever it is you are interested in recording. So the first step is to give everything a name. A system needs to be developed from the outset that gives a structure to the names assigned to each object so that time is not wasted making decisions and objects are not lost or duplicated due to incorrectly remembered names (Nickerson 1994, 1996).(3)

What can be measured is points and surfaces (defined by collections of points). Objects represented by a single point might be outlets or switches, and surfaces might be walls or floors. More complex objects such as stairs, cabinets, furniture etc. will be handled in the model by inserting symbols to represent them so they can generally be defined by two points, one for insertion point, one for rotation, perhaps supplemented with some dimensions. The bottom line is that what we are determining is points in space and their characteristics. An ordered list of these points, grouped according to the objects of which they are a component, can be used to automatically generate the model.

image (14k) The information we are collecting is, for the most part, implicit in the individual objects we measure. The figure above indicates the different types of information, how each might be captured and the path this information follows between the field and the electronic record. From the beginning this information must be carefully organized and as easy as possible to locate. We do this by means of an object name with which we christen each object as it is encountered and which becomes the key for all measurements, notes, photographs and sketches that follow. It is this framework that the CART system uses to generate the model and link the automatically generated graphics to all the other information concerning the object.

image (36k) The result is a Site information System as outlined above which uses the Autocad model as a front end, the geometric database as an index and as many supporting files in as many different formats as seems appropriate. The only limitation is that all these files follow a consistent naming formula based on the object name.(Nickerson 1994)

The Database

    PT_X    PT_Y    PT_Z   P_NO  P_ID   O_NA   SZ_X    SZ_Y   SZ_Z  UV_1COMMENTS
315.0002.8280.0000.0FS  UCS1               foresight
 0.0000.0000.0001.0 W   W1           2.5004start of wall 1 2.5 high
 1.0000.0000.5001.1 win W1       0.100   2 lower left window point
 2.0000.0001.5001.2 win W1               2 upper right window point
 4.0000.0000.0001.3 W   W1               1 end of first wall segment
 0.0000.5000.0001.4 W   W1               3 jogs 0.5 from recorder
 6.0000.0000.0001.5 W   W1               3 continues in X (layer 3)
 0.000-0.5000.0001.6W   W1               3 jogs towards recorder 
 7.0000.0000.0001.7 W   W1               4 end of wall 1
 0.0002.8280.0001.8 0   W1               4 origin of "W1" in ADZ
113.0005.3850.0001.9X   W1               4 direction of "W1" in ADZ
  
The database read by the software looks something like the above. Required for each point collected are the real numbers that will locate it in 2D or 3D space, a point identifier which indicates the drafting function of each point and a unique object name that groups the CAD entities into useful units and provides the links among database, CAD drawing, photographs and text files. There is also a unique point number to allow for sorting and trouble shooting in the case of missing or erroneous values. Scaled symbols require additional values for their size and these values are also used for things such as wall heights. Optionally there are several short text fields and a comment field that accept descriptions or values that can be used in layering, symbol naming etc. and to store any other relevant information about an object.(4)

To facilitate both note taking in the field and entry into the computer, data input sheets were prepared for each project so that the data fields can be laid out in the order in which the measurements and notes are taken.

image (3k) At Humeima the measurements came first, in a polar- cylindrical format (angle,distance,depth) followed by the point number, the object name and some optional keyword fields

image (55k) At Mclean Mill the geometric information (X,Y,Z coordinates) was collected automatically using a total station(5) so these fields did not appear on the recording sheets and the first entry was the point number. However each board required values for its length, width and thickness (fields never used at Humeima), and keywords and comments were used extensively.

There are a number of subtleties that can be applied to the data collection. Like any tool, as it becomes familiar shortcuts and features of which the programmers may not even be aware suggest themselves to the user. For instance, some points can be skipped because of assumptions made by the software, extra points can be taken to supply wall heights and values can be added to add thicknesses to most objects.

Data Input

image (136k) At the end of a day in the field the measurements collected must be entered into the database for subsequent processing. At Humeima this meant manually keying in this information on any available computer. Luckily archaeology moves slowly and, when working in teams of one reader and one typist, fifteen or twenty minutes would usually suffice though it could take an hour or longer when floors or walls that needed stone by stone treatment were encountered.

image (183k) At Mclean Mill the point coordinates were already in the memory chip of the total station so these were downloaded directly to the computer and the annotations and hand measurements supplementing the survey data keyed in as described above.

image (40k) In the future it is hoped that programming the total station to accept all the keywords and annotations that we have been recording manually will eliminate the data entry task. Where the computer can be kept out of the elements, such as for facility recording, data can be captured directly from the survey instrument, annotated on the computer and the model generated on the spot, before changing stations.

Configuration Settings

The first step in initiating a CART project is the preparation of the settings sheet. This file provides the opportunity for the user to customize the CART program. In it drafting parameters are set, and the composition of block and layer names are determined. Once satisfactory settings have been determined for a particular model type it is unlikely that they will have to be altered and future projects of a similar type can be initiated by simply changing the project variable. It is here that one specifies the type of measurement that were collected (XYZ, polar or running dimensions), point annotation options (size, angle & layer) and information definitions such as what database fields to use for attributes, layer names and extended entity data (EEDs).

Symbology

The second step is the preparation of any specialized symbology that might be necessary to fully process the data. There are two types of symbols that may be used in the model. One is the unit or 1x1x1 symbol which may be based on a single record and used simply as a connection to the database that describes the object represented. By default they are inserted at a standard scale determined by a variable from the settings sheet though if values are entered for the X, Y & Z scale factors these will be used instead. Optionally, a second point can be used to define the rotation angle and the positioning of an object can be further enhanced with the addition of a third point which allows the definition of a complete coordinate system for the insertion of the object. The library supplied with the software contains several of this type of symbol and if others are needed they can usually be created by copying one of the existing ones to a new filename.

The other type of symbol is drawn to real world scale and inserted with either two or three defining points. The most common example of this type would be a furniture library representing a real inventory such as might be needed for a facility drawing. These would need to be created prior to generating a drawing which specifies their insertion. It is possible to use unit symbols for furniture though the scale factors for each individual component would have to be entered, a much more time consuming exercise than the creation of a symbol library.

Building the Model

image (16k) To the user the generation of the model is simply a matter of choosing the "generate" option from the menu. The database is sorted by point number then read by Autocad, each record adding a point to the drawing. Much of the time the record will trigger some Autocad function, a line or insertion for example, and in other cases, such as arcs and coordinate systems, several points are needed before the Autocad function can be processed. Whenever there is a change of object name all entities associated with the name just closed are blocked and reinserted on a layer determined by the database entries for that object.

DataBase Integration

As useful as the graphic component of this tool is, the potential of the associated database is probably much more significant. A recorder measures things and make notes, and other than some clarifying sketches, the graphic representation of this data is just a by-product of the original record. In most cases the CAD model created by this method need not even be saved as it is just as easy to generate it again as it is to retrieve it, and next time you may want to represent it differently. For instance, by changing some global parameters in the settings sheet, different layer groupings can be generated, and component drawings can be created of only those objects identified by a pre-defined or interactive SQL (Standard Query Language) query. This functionality can provide a way to keep large databases, and potentially huge drawings, manageable on normal computer equipment, even laptops. As each object is drawn, it is labelled with extended entity data linking it with the database that created it, and when queried from within Autocad all records in that database are displayed. In the case of named blocks such as furniture, doors or pot sherds, access can also be provided to other database tables specific to that class of object. This Xdata is also used by pre-defined queries that will display any text files or raster images (photographs, sketches etc.) associated with the object. The database, when stored in comma delimited format, occupies an absolute minimum of disk space and, in this form, it is even possible to e-mail it to another site as pure ascii text. There it can be generated and the resulting model analyzed by the specialists who, without having to visit the site, might be able to make recommendations on where the recorders should concentrate their efforts or on elements that may need more detailed study.

Applications

Though it was conceived in response to a problem in heritage recording and tested in an archaeological environment, this tool is foreseen as having a wider application in more general architectural practices. The recording of the existing situation is always the first step in any renovation, and the possibility of collecting the necessary measurements in a way that will provide a drawing while the recorders are still on site and able to correct the errors and omissions that inevitably occur should be greeted with considerable enthusiasm; but probably the most promising application of this technique is the capture of the as-built and as-furnished situations of large commercial installations where the combination of laser measuring technologies and the automatic insertion of symbology promises to reduce the time required for data capture and CAD modelling to a fraction of what has traditionally been required.

Conclusion

We have a working Computer Aided Recording Tool with a number of useful features.

1. It can provide completely automatic generation of a model from downloaded survey information, convenient forms for the recording of measurements and keywords for later input into the database for later generation, or anything in between.

2. The CAD model generated is distinguished by the fact that every object in it is a symbol, bearing a name given by the recorder, and because of this structure it acts as a 3D graphic index to all electronic data bearing an associated name.

3. The database is easily reduced to a flat, comma delimited file for simple storage and transmission. Though only the Autocad generation tool has been written to date no difficulty is anticipated when using the same database to create models in other graphic formats.

There are some additions and many refinements we would like to implement in order to make it more versatile and less user belligerent but even in its present form it can be used to do real work. Chance has determined that the field tests to date have been archaeological rather than architectural but it is clear that the functionality demonstrated in these projects is immediately applicable both for recording the as-found situation prior to renovation and to facilitate the building of a model during an FM survey.

Sample Database and the Resulting Objects

image (135k) image (61k)

Endnotes

1. The McLean Mill National Historic Site is being developed by the city of Port Alberni, British Columbia with the support of David Whiting, a restoration architect with Parks Canada.

2. Humeima is a site in southern Jordan representing occupation from the 2nd century BCE to the 7th ACE which is being excavated under the direction of Dr. John Oleson of the University of Victoria and the Jordanian Department of Antiquities.

3. When recording a building we name the first room you enter "R1" (Room 1) the wall you walk through to enter it "R1W1" (Room 1, Wall 1) with the next in a clockwise direction "R1W2", the door you walked through "R1D1" and so forth.

4. There is also an optional field for a rotation angle that is not applicable in the field. This allows the software to be used in cases where databases are being created from existing CAD drawings, such as are commonly used for facility management. In this case symbol rotation is stored along with insertion point and scale factors as an interim step in the process of creating the links between drawing and database. An application of this program that allows the intelligence in a drawing to be extracted to a database and that database used to recreate the CAD model, fully linked, in another system.

5. The "total station" is an electronic land surveying instrument that combines an electronic distance measuring instrument, an electronic theodolite, a microprocessor and a memory storage system. It is set-up over a known point, referenced to a second known point, and a signal is bounced off a reflector at an unknown point. The microprocessor then computes the distance and angles in both the horizontal and vertical planes to locate the unknown point in a three- dimensional coordinate system and the data is stored in the memory device, eventually to be downloaded to a computer. In addition to the coordinate information the operator has the option of tagging the data with a point number, point code, keywords, etc. by entering the relevant data from a keypad on the instrument.

Bibliography

Nickerson, S. 1994 A Site Information System (SIS): CADD/Database Integration for Field Use. APT Bulletin 24(1):56-62 /steve/sis.txt

Nickerson, S. 1995 CART Modeller Users Manual (c) 135479 Canada ltd. - unpublished /acart/cart_man.txt

Nickerson, et al. 1995 Integration of Measurements and the Knowledge Base to Generate a CAD model on Site. proceedings of ACADIA '95 University of Washington, Seattle /steve/acadia.html

Nickerson, S. 1994, 1996 Object Oriented Recording /steve/oor.html

O'Brien, H. 1994 Computer-Aided Recording: Proper Documentation for a New Technology APT Bulletin 24(1):52-55

Partridge, R. 1994 CAD and Its Emerging Role in Historic Conservation: A Case Study APT Bulletin 24(1):38-39

Streilein, A. 1994 Towards automation in architectural photogrammetry: CAD-based 3D-feature extraction ISPRS Journal of Photogrammetry and Remote Sensing, 49(5):4-15 http://www.p.igp.ethz.ch/p02/projects/dapcad/dapcad_papers.html

More up to date information concerning the CART project may be found at: http://nickerson.icomos .org/acart/


Last change: 29 February, 1996 (Steve Nickerson) steve@icomos.org