Blair C. Parker
Raymond J. Hintz
University of Maine
Jerry L. Wahl
Corwyn J. Rodine
USDI-BLM-Eastern States Office
Recent advances in electronics miniaturization have provided cadastral surveyors with DOS-based hardware platforms small enough to be taken into field surveying environments for use in real-time digital collection and analysis of survey data. These new hand-held personal computers will have a profound effect on data collection and data analysis procedures. For the first time, software developers will be able to write survey collection and analysis software in high level programming languages for use on hand-held computers.
An electronic survey data collector has been developed which utilizes a state of the art, text based user interface [Goodwin, 1989] to perform real-time survey data collection and analysis on a hand-held PC. This data collection and analysis system provides a streamline method for incorporation of survey data into a PC based measurement management software system. Combined, these two software systems become mutually supportive. One supplies data for analysis, while the other supplies updated results for use in subsequent data collection This occurs in a completely digital environment.
The primary design goal of the Cadastral Electronic Field Book (CEFB) was to provide cadastral surveyors with a tool with which they could more easily collect, analyze, and automate cadastral field surveying and computational processes. CEFB was not intended to be a collection package for all types of surveying. Specifically, CEFB was designed for cadastral surveys where large amounts of traverse data, evidentiary information, and geodetic computations are involved.
Different survey requirements dictate that different data collection practices and procedures should be used. A good example of this is the case of engineering design surveys. The Florida Department of Transportation (FDOT) has recently developed a highly automated survey data collection and manipulation software system [FDOT, 1989, 1991]. This system provides excellent data collection capabilities which include concepts such as chaining, feature coding, instrument calibration, time tagging, etc. Data which has been collected with this system can be transferred directly into a CAD format digitally, including line work, attribute information, and surface model definition.
The FDOT Electronic Field Book (EFB) type of collection system is, however, inefficient for the purpose of cadastral surveying. Cadastral surveyors require geodetic computation capabilities, highly automated and versatile textual data storage capabilities, and a good sense of where their traverse stations are in respect to some pre-defined 'true line' (in a geodetic system). Cadastral surveyors do not need an electronic data collection system which was designed primarily for site mapping surveys.
Commercially available electronic data collectors are inadequate for cadastral surveys for several reasons [Wahl et al., 1991]. Most of the reasons can be combined into three general categories. First, commercial electronic data collectors are restrictive in their operational use. Many data collectors, for example, require the operator to distinguish between 'traverse' data and 'sideshot' data, and will only allow a specified number of sightings to any single station.
Secondly, commercial electronic data collectors do not provide for computations involving earth curvature and meridian convergence corrections. In typical cadastral survey situations this can account for several minutes of angular error from the eastern extremity of the project to the western extremity.
And third, commercial electronic data collectors do not provide adequate capabilities for the digital collection of evidentiary data. This evidentiary or textual data is an integral part of the cadastral retracement survey. A large amount of this data is included in the official field notes for the survey and an automated method for dealing with this type of data needs to be developed [MacDonald, 1992].
With regard to the design goals listed above, CEFB must perform two basic numerical operational functions. CEFB must store original (raw) survey observation data and it must be able to perform operations on this data to supply the surveyor with additional, computational information.
In addition to data collection and on-board computational capabilities, CEFB should provide for easy incorporation of collected survey data into the Cadastral Measurement Management (CMM) survey observation analysis system [Hintz, 1988, 1990], [Rodine et al., 1991], [Blanchard, 1991], [CMM Manual USDI, 1991]. CEFB was designed to supplement the computational power of CMM by supplying survey observations digitally (instead of keyboard entry) and to benefit from CMM by using the post-processed coordinates that were computed from the analysis procedure.
In an operational environment, survey observations are measured and stored by CEFB. The operator would then incorporate these observations into the CMM analysis routines for verification and cadastral survey type geometry computations. The result of this process, new coordinates, may then be transferred back to CEFB for use with any ensuing field work. Thus CEFB and CMM are mutually supportive of each other. CEFB provides easy data input for CMM and CMM provides CEFB with up-to-date coordinate information.
It was decided that CEFB would demand only the hardware specific requirements of available display screen of at least 16 lines by 40 characters wide, the operating system must be 100% DOS compatible, there must be at least one standard serial port available, there must be at least 300K system RAM available, and at least 512K of disk space available.
CEFB Main Menu Screen
The first thing that appears on the computer screen when CEFB is invoked
is the CEFB main menu. From this menu, operators are able to perform two
basic functions: They may select or define several of CEFB's global variables
(data file names, default variable settings, etc.) or they may select between
one of five data collection/processing modules. Figure 1 shows how an initial
main menu screen would look.
Wed Mar 11 14:45:07 1992 (PST -8)
The main menu screen contains four distinct areas of interest: A pull-down menu bar on top, a 'file info' display in the center, the current time/date/timezone on the next-to-last line, and a 'shortcut' bar on the bottom line.
The pull-down menu bar contains menus which are activated by pressing the <ALT> key and the hot-key (flashing letter) simultaneously (eg. to activate the 'Options' menu press the <ALT> key and the 'O' key simultaneously). This will activate, or display, a menu containing several functions which may be invoked by the operator by pressing the indicated hot-key, or by using the up/down/left/right arrow keys to highlight the appropriate function which is activated by pressing <Enter>.
The main display will always list the currently defined Field File (.FF), Coordinate File (.CF), Feature Code File (.FC), computational datum, State Plane Coordinate System (SPCS) state, and SPCS zone. When one of these items is changed by the operator, the change is indicated on this file information display. Additionally, when a change is made in any of these items, the change is written to a configuration file which will be used by CEFB until the operator makes another change.
The 'shortcut' bar contains several items which relate to menu items. To select a particular item press the key corresponding to the capitalized letter in the function desired. This gives the operator two different methods of executing selected functions. The first is by activating the appropriate pull-down menu and then the desired function. The second is by pressing the hot-key from the shortcut menu. Not every function has a corresponding shortcut key. Typically only the most frequently executed functions will have shortcut keys.
The major components of CEFB are listed in the 'Function' menu. The five functions are also shown in the shortcut bar of Figure 1.
The 'Survey data coll.' function is the CEFB module where typical survey data collection would be performed. This module allows operators to define a typical survey setup (BS, OCC, FS) scenario and collect information from an electronic total station. This information is then analyzed and displayed to the operator in several forms on the computer screen. Additionally, this information is used to compute coordinate values for the foresighted station (if the coordinate file is defined). Finally, this observation may be stored, along with any desired textual information, in the field file for post processing with CMM.
The 'Astro data coll.' function is the CEFB module where astronomic data collection would be performed. The astronomic data collection module allows operators to define a typical astronomic survey setup (BS, OCC, sun, polaris, or other star) scenario and record simultaneous time, horizontal, and zenith circle readings from an electronic total station. The collected data is then analyzed and an azimuth to the backsight is computed and displayed. Astronomic data may then be stored in the field file for
The 'COGO' function is the CEFB module which performs all of the coordinate geometry functions. In this module, operators are able to input or list coordinate values, compute inverses, traverses, or bearing/distance intersection combinations. All of these routines are performed geodetically (if a SPCS zone is defined) or in plane cartesian coordinates as defined by the operator.
The 'Trueline' function is the CEFB module which displays information relating a surveyor's position to some operator defined 'true line'. A true line is any line with existing coordinates at two end points. Some examples of derived information include perpendicular offset, horizontal angle required to turn to perpendicular offset, angle to turn to parallel line, down line distance, etc. Trueline information is computed either geodetically or in plane cartesian coordinates, depending on user definition.
The 'Read/Edit .FF file' function allows operators to view and/or edit
survey data. The Read/Edit module allows operators to review observations
and edit certain portions of this data. Certain portions of this data are
un-editable, and certain rules apply to the deletion/modification of the
CEFB SURVEY DATA COLLECTION MODULE
A typical survey 'setup' must be defined. In CEFB a setup is defined by three parts, the backsight (BS) station, the occupied (OCC) station, and the foresighted (FS) station(s). Every setup will have at least one BS, OCC, and FS station. Additionally, every setup will have at least one repetition associated with it. A repetition is defined as the collection of all FS stations containing the same BS horizontal plate reading. A typical setup containing one direct and one indirect (reverse) sighting to one or more FS stations would have two repetitions containing one FS station each.
The survey data collection module in CEFB was designed with two fundamental concepts in mind. CEFB should not control or direct the process of data collection, and CEFB should display to the operator a clear and concise representation of the data which the operator wants to collect.
The first of these concepts means that the operator, not the machine, is in control of how data is collected. Far too often survey data collector software dictates to the operator the order or process of data collection. Since this limits a survey operation, data collection in CEFB is controlled entirely by the operator. The operator directs how many FS stations to observe and when to observe them. There is no pre-determined number of FS stations per repetition or how many repetitions per setup are allowed in CEFB.
The second design concept states that the operator
should be able to obtain a clear representation of the survey data on the screen. He or she should not have to perform several keystrokes or sort through a lot of meaningless information to look at the data that the instrument has just collected.
CEFB ASTRONOMIC DATA COLLECTION MODULE
The astronomic data collection module in CEFB was created in response to a need for an automated method of astronomic data collection and real-time azimuth computation. The digital collection portion of this problem has been solved, by default, by the simple fact that CEFB was designed to perform specifically this task. Real-time azimuth computation, on the other hand, requires more software implementation.
The computation of azimuth from celestial bodies is accomplished through the use of relatively simple mathematical functions based on a set of survey observations, corresponding observation epochs, and a number of predictable astronomic 'constants'. The major problem in azimuth computation, therefore, is not with the azimuth computation so much as it is with the computation of the astronomic constants, which are periodic functions of time. In order to compute azimuths of acceptable precision, the astronomic constants must also be computed to similar precisions.
Historic methods for the computation of astronomic azimuth have focused primarily on the use of astronomic tables, where astronomic quantities were precisely computed, and tabulated, at fixed intervals of time. The user could, therefore, obtain desired quantities for any given epoch by simple interpolation of these tables.
During the design phase of CEFB it was determined that the best, initial course of action with regard to the computation of astronomic azimuth would be to automate the interpolation method for astronomic quantity computation. While this methodology was less desirable than an automated computation of quantities based solely on time, the implementation of such an interpolation algorithm greatly reduced the effort required to successfully implement a real-time collection/computation module. It is anticipated that an effort will be made in future releases of CEFB to deal with the computation of astronomic constants more effectively.
In order to compute astronomic azimuths in real-time, CEFB requires the following:
1) The SPCS Datum in CEFB must be set to a valid zone, so that latitude and longitude can be computed.
2) The latitude and longitude of the occupied station must be defined in the coordinate file.
3) The Greenwich hour angle, declination, and semidiameter (if applicable) must be defined.
This may be performed manually or automatically. The first two requirements assume that CEFB has access to the latitude and longitude of the occupied station. The computation of astronomic azimuth requires that this information be known.
The third requirement has to do with the way in which CEFB acquires ephemeris information. In order to automate the interpolation process, a data file has been provided, which supplies digital ephemeris data for use in the interpolation process. This file must be named 'year.EP', where 'year' is the current year in 4 decimal digits.
CEFB COGO MODULE
The CEFB COGO module is where operators would go to perform traditional coordinate geometry routines.
This main COGO screen contains only three basic sections: The top line is the pull-down menu bar, the bottom line is the shortcut menu bar, and everything in between is display space for the work that is performed in this module. As the amount of information displayed fills up this display space, it will scroll upwards off the display area. This information may be re-displayed at any time the pull-down menu bar is active by pressing the up, down, page_up, or page_down keys.
The COGO module requires that a coordinate file be defined before any computations will be initialized. Every coordinate computed is stored in the coordinate file (project.CR).
CEFB COGO is a three dimensional coordinate geometry module. Whenever a new position is computed, it will require the input of an elevation for the new station. When computations are performed in a geodetic mode, the vertical component of each station is taken into consideration and utilized for the specific computation.
CEFB COGO operates in either a geodetic or a plane cartesian coordinate mode. The use of one or the other mode is transparent to the operator. If a SPCS zone is defined, it is assumed that all computations are to be geodetic [Bowring, 1981], [Claire, 1968], [Stem, 1989]. Conversely, if no SPCS zone is defined, all computations are assumed to be cartesian. While in geodetic mode, if grid computations are desired the operator must re-define the coordinate datum to 'plane'. Similarly, if the operator wanted to perform geodetic computations he or she must re-define the coordinate datum to either 'NAD27' or 'NAD83' along with the corresponding SPCS zone.
CEFB TRUELINE MODULE
The 'Trueline' module in CEFB allows operators to obtain quick information relating their traverse stations to a theoretical 'line' or point. The first three lines on this screen describe the defined 'true line' along with it's associated bearing/azimuth and distance. The true line is an operator defined line represented by two points which are defined in the coordinate file.
The next two lines describe the traverse setup (BS and OCC stations). Also shown here is the associated bearing and distance for this related information.
The remaining information relates the previous two items to each other. This section is broken down into three rows of information which, in turn, is broken down into four columns. The first row relates the defined traverse to a user specified point, the second row relates the traverse to a line parallel to the defined true line, and the third row relates the traverse to a line perpendicular to the true line.
The first column in this section identifies what is related to the instrument setup. The second column contains the horizontal angle which must be turned in order to traverse to the specified object, while the third and fourth columns indicate what the bearing and distance is to the specified object.
The 'Read/Edit .FF file' module in CEFB allows operators to review and edit portions of the field file.
In the 'Read/Edit .FF file' module, the up /down /left /right arrow keys operate exactly as they do in the 'Survey data coll.' module. The up/down keys scroll through survey repetitions while the left/right keys scroll through the available FS fields. Unlike the 'Survey data coll.' module, however, the operator may scroll through different setups by pressing the 'N' (next) and 'P' (previous) keys on the keyboard.
The editing feature of this module will allow operators to delete, un-delete, or modify portions of the observational data contained within the field file. However, in order to maintain a certain amount of data integrity only certain portions of the data may be edited. Furthermore, once a particular observation has been edited, the original observation is forever 'tagged' [Onsrud, Hintz, 1991] and the newly edited observation is inserted into the data file immediately following the modified observation (if the original observation was modified).
Only observational data may be reviewed/edited. At the current time no facility has been incorporated into CEFB to perform these operations on textual data. That is, textual data which documents or describes a found monument, for instance, may not be altered or added to once entered.
TRANSFER OF DATA FROM CEFB INTO CMM
Survey data collected with CEFB is stored in a binary field file (.FF). In order to analyze this observational data it must first be transformed from binary to ASCII format and, secondly, it must also be reduced (abstracted). Remember that while CEFB displays meaned angular and distance information, it stores only the raw survey observations in the .FF file. Meaned angles and distances, not individual observations, are included in the CMM .LSA data file for analysis.
COORDINATE TRANSFER FROM CMM TO CEFB
CMM stores coordinates in an ASCII coordinate file named project.COR. CEFB, on the other hand, stores coordinates in a binary coordinate file named project.CR. Additionally, CMM allows 16 character alpha-numeric station names while CEFB allows only 8 character alpha-numeric names. These differences are primarily a result of the restrictive environment that CEFB was designed to operate in, with respect to available disk space, computer RAM, and computer display space.
Transfer of Coordinates From CMM to CEFB
There is an option in CSTUF.EXE (part of CMM) that allows users to create a CEFB ready coordinate file directly from any project.COR file. The procedure for performing this transformation is documented in the Help facility of CSTUF.EXE (F1 key) on page 17 of the distribution help screen.
All the user must do to create a binary project.CR file is enter CSTUF.EXE, and press the <Control>-<F5> key combination. Next, the user is prompted for a file name that he or she wishes to create. The user must add the .CR extension to this file. CEFB will not recognize coordinate files with any other extension.
Once the project.CR file has been created, it is only a matter of transferring this file onto the data collector and defining this file as the current coordinate file ('Open coor. file'). It is always a good idea to list a couple of coordinates in COGO just to make sure that there were no problems during the data transfer process.
It has been illustrated that electronic survey data collectors can be developed which will aide the cadastral surveyor in the daily execution of his or her work. By utilizing hand-held DOS based computers as a hardware platform and a high level programming language with which to write application software, an electronic survey data collection system has been developed for the cadastral retracement surveyor. This survey data collection system is highly efficient, intuitive to use, provides cadastral surveyors with real-time geodetic computation capabilities simultaneously with electronic data collection, and does not dictate to individual surveyors the method by which data will be collected.
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