Corwyn J. Rodine
Bureau of Land Management
Eastern States Office
Jerry L. Wahl
Bureau of Land Management
California State Office
Barry M. Blanchard
Raymond J. Hintz
University of Maine
Cooperative work between Cadastral Survey of the Bureau of Land Management and the University of Maine has resulted in development of an integrated Measurement Management software system specific to retracement cadastral surveys in the U.S. Public Land Survey System. The software is now in a beta release phase. This paper will provide some background for the unique application requirements and a progress report on the system development. The paper will provide descriptions of many of the capabilities of the system, and a brief discussion of the many challenges that have faced this development.
Cadastral Measurement Management (CMM) is an ongoing software development effort between the Bureau of Land Management and the University of Maine which began approximately 2 years ago. The beta version of CMM has undergone a series of tests within BLM. The result is a system of integrated programs which are specifically designed for dependent resurveys within the U.S. Public Land Survey System (PLSS).
Base design considerations of CMM are:
The development of CMM was deemed necessary because no available software package on a personal computer met the four base design criteria.
While the software development was performed primarily at the University of Maine, the Bureau of Land Management had a great deal of interaction in its development through the Cadastral Technical Advisory Group (CTAG). This group was selected based on their experience with automation in cadastral surveying, and consists of Corwyn Rodine (Eastern States Office), Jerry Wahl (California State Office), Tom Noble (Denver Service Center), Tom Wohlend (Alaska State Office), and Bernard Hostrop of the Washington Office. CTAG meets at the University of Maine at least twice a year for one week time periods, and interacts with University personnel on a regular basis as updates to software are provided and tested.
To perform primary testing of the alpha version of the software, a primary test site was needed. Each BLM state office interested in performing the beta testing was required to submit a proposal detailing why they could provide an effective testing mechanism. Offices could also request to serve as secondary test sites. The role of the secondary sites were to provide verification of findings of the primary site.
Though the selection of the primary test site was difficult due to several fine proposals, the Montana State Office was awarded this role. The software was demonstrated to BLM personnel at the March 1990 ACSM-ASPRS meeting in Denver, and during the following week CTAG and University personnel provided initial training to surveyors at the primary test site. Several other state offices also had representatives at this week of training. It was their role to return the software to their office and serve as a secondary test site.
Surveyors at the Montana State Office spent the next two months processing existing data sets through CMM. Each week a status report was provided to CTAG and all BLM cadastral surveyors involved in alpha testing. This essential user feedback was accomplished through the use of the Bureau's electronic mail system. This information was then discussed with University personnel with specific regard to program modifications and further documentation needs.
A follow-up visit to Montana by CTAG and university personnel was made two months after the initial visit. This one week period allowed more thorough "question and answer" sessions to be held since Montana personnel were now users instead of beginners in processing data with the software. This meeting also enabled better forming of the final test report by the Montana State Office.
During the summer of 1990 a series of program modifications resulted from this initial testing, and a more extensive user's manual was prepared. This resulted in the beta release of the software within BLM Cadastral in September 1990.
A CTAG meeting in December 1990 resulted in final required updates before CMM ver. 1.0 is released at the 1991 ACSM-ASPRS meeting in Baltimore.
The extensive interaction between University and CTAG, along with the excellent testing provided by the primary and secondary test sites, has resulted in a very beneficial relationship (Hintz and Rodine, 1990; Blanchard, 1990). It has also resulted in a software system which has been extensively tested and modified for user needs.
Getting Started. While every dependent resurvey is unique and therefore cannot be generically categorized, an attempt is made here to describe how a survey would proceed using CMM.
While geodetic positions for PLSS corners and traverse stations are computed using CMM, it is important to document that these are a necessary by-product of the process (Hintz, et al, 1988; Hintz and Onsrud, 1990). Survey measurements are preserved in the system, and as more measurements are added, positions of points are updated. The relative geodetic relation of points is of critical importance as opposed to absolute position.
The first problem confronted by the surveyor is location of geodetic control near the dependent resurvey project area. Since some surveys could be in areas essentially devoid of control, the use of a "scaled" position from a quad sheet will allow CMM to apply correct geodetic analysis to the data in the aforementioned relative relationship. If a survey will eventually tie to geodetic control, it is possible to work from a scaled position until the survey network ties to the control point. At that time the scaled position is easily eliminated as a control point.
While not critical in use of CMM, a surveyor will usually find it beneficial to create a digital copy of the official record survey information. To enhance automated computational procedures, CMM can make use of a standard corner identification number which conforms to BLM's Geographic Coordinate Data Base GCDB. A program called INREC (INput of RECord information) enables efficient input of the record information, and affords the user with a number of testing procedures for correctness of the entered data. The correctness of the digital record information is of utmost importance in the dependent resurvey, and the thorough checking of its validity cannot be overemphasized.
Data Entry. In an ideal scenario, collected field data should be input to CMM daily. This philosophy can easily be overridden by busy field days and other duties, but their are several reasons why entry on a daily basis is useful.
The testing by the Montana State Office showed that data entry through keyboard input was very monotonous and error prone. This was especially true in the testing since complete jobs were being entered at one time. Entry of a small amount of data (such as a day's work), followed by verification of the data through the analysis routines in CMM, enables the user to look for problems in a finite amount of data if the previous data has been verified.
The best solution to the data entry problem will be direct input from field data collectors. This has already been accomplished for existing data collectors being used within BLM, and will be further resolved with the development of the BLM Cadastral Electronic Field Book (Wahl, et al., 1991).
Keyboard entry of data is accomplished through a dedicated entry/editor system within a CMM program called GENER. GENER's other critical role is coordinate generation in a conventional coordinate geometry sense. For dependent resurveys the coordinate generation is almost entirely from traverse type computations. GENER requires no specific ordering of data, and thus traverse routes with closure reports are generated for any data order. The closure reports are extremely useful in blunder detection prior to least squares analysis. GENER also allows generation of only new station coordinates, thus preserving existing adjusted values if desired. GENER provides a multitude of error messages for items such as inability to generate coordinates for all stations.
If the data appears blunder-free the most important role of GENER is that approximate coordinates have now been automatically generated for any traverse network, and these approximations fuel the ensuing parametric least squares analysis.
Least Squares Analysis: The successful use of least squares analysis of dependent resurvey data has been discussed in Hintz and Rodine (1989). One of the critical items in acceptance of CMM has been the demonstration that data sets processed thus far reflect statistically insignificant amounts of adjustment to measurements. The use of least squares has thus become a process of verification (analysis) that the geometric constraints of redundant data do not require unrealistic adjustment of any field measurements. Since resulting coordinates are geodetic in nature the software has the ability to handle meridian convergence and projection scale factors automatically, and elevation information can be provided by the user at a level of complexity ranging from a single project elevation to individual elevations for each traverse station.
The user has the ability to assign project default error estimates, and override any of these with individual measurement values or a similar estimate for a series of measurements. The latter being critical in the execution of a Dependent Resurvey, because in "following the footsteps of the original surveyor" , one often finds oneself in stretches of nasty terrain such as swamps and bogs. One of the most important items noted in testing is verification of the surveyor's ability to estimate his own measurement error. Error ellipse information of final positions are also available to the user.
Users also have the ability to use the least squares analysis in blunder detection through residual examination and standard robustness techniques. A user must be aware that these technique's successes rely heavily on the geometry and redundancy of the survey network.
The final important item in the least squares analysis was the ability to adjust very large networks on a personal computer. The beta version release of 3000 stations has already been exceeded by a job in Arkansas which consisted of an entire township with significant section subdivision work, and thus a version capable of larger adjustments will be available for these special cases in release 1.0 of CMM.
Traverse Reports: Since the least squares analysis does not provide conventional traverse closures a program called CHECKER performs this function automatically. Conventional latitude and departure closures, linear precisions, and angular error of closure are generated both in an automated fashion and by user definition. CHECKER has also been used extensively for blunder detection purposes since it reflects the amount of adjustment which has been applied to a series of measurements.
Computerized Viewing of Survey Network: Users are able to obtain graphical representations of their survey network using two separate methods. A quick view of the survey network is available if the PC is equipped with a graphics adaptor using a program called VIEW. This program has recently been modified to include pan and zooming operations, allowing users to view any portion of their survey network very rapidly. CMM also has the ability to create a standard DXF file for viewing with CAD software. The later option is also being used for input of information to CAD for final plat preparation.
The aforementioned analysis routines can be utilized for any type of surveying, and thus are not restricted to dependent resurveys or retracements within the PLSS system. The following cadastral computations are, for the most part, internal to PLSS computations.
Manual Proportioning using the record file: The traverse network eventually provides suitable information to enable single and/or double proportionate measurement for search locations or for recomputation of corners deemed lost. The user has the ability to identify a corner, and computer program PROPORT automatically searches for controlling corner information and necessary record information. If this information is available the computation is performed according to the Manual of Surveying Instructions, 1973 and a report is created which details this information. The report can be stored as a file for later referral as to the order and basis of computations which the surveyor performed.
Automatic Proportioning using the record file: If GCDB point identifiers are used, CMM has the ability to analyze controlling positions and the record file, and automatically proportion the entire data set. This ability is extremely useful in determining search positions for corners, and at the end of a job can be used for final determination of all positions of corners which have been identified as lost. A significant report is generated so the user can thoroughly check this automated process. The program is also being used as an aid in evaluating the reliability of local monumentation as one can compare where they are located relative to a proportionate position from found original corners.
Geodetic COGO (CSTUF): One of the most important tools for the cadastral surveyor is the ability to perform coordinate geometry computations in a geodetic framework. With this program the user can add, delete, and list coordinates in either geodetic or cartesian coordinate (plane) mode. The conventional coordinate geometry operations of bearing-bearing intersection, distance-distance intersection, distance-bearing intersection, coordinate inversing and traverse computations can be performed in either geodetic or plane mode, and any geodetic bearings can be identified as forward or mean in nature. Geodetic and plane midpoint round out the computational options along with area computations. Basic horizontal curve computations are being added in ver. 1.0.
Viewing of PLSS information: The user has the ability to graphically illustrate what corners have been positioned, or where temporary corner positions have been located. This is performed through use of a computer-screen version of a township diagram with graphical identifiers for all information.
Corner moves and true line offsets: These functions are analogous to layout in a dependent resurvey sense. A corner move returns a set of angle and distance combinations from existing stations which identify a geodetic position. This function could be used for setting both temporary and final corner positions. Once true line has been identified through retracement or restoration, true line offsets in the form of angle or bearing and distance can automatically be generated from all traverse stations within a user-defined distance from the true line.
Miscellaneous utilities: This program enables proportioning without use of the digital record file. This is also the program where "adjustments" within the Manual of Surveying Instructions such as broken boundary, irregular boundary, etc. are performed. This program also has the ability of performing one, two, or three point control computations in accordance with the Manual of Surveying Instructions, 1973.
It is important to recognize that the two components of CMM are used in unison on a continual basis. Survey measurements are entered, analyzed, and verified. This additional information is used to update search positions for corner locations. As monuments are found and identified these corner locations are used as controlling information in ensuing cadastral computations.
The survey measurements are thus used in providing better information in the dependent resurvey process. Each job will be unique in how information is collected and utilized.
A cadastral measurement management software system has been developed through co-operation between the Bureau of Land Management and the University of Maine. The software system is flexible in that all of the computational complexities of the U.S. Public Land Survey System can be resolved in a geodetically correct fashion. The software has been placed through extensive test procedures and revisions in the realization that only this approach can result in a system which will be useable by the general surveying community.
The authors wish to especially thank Steve Douglas, Mark Dixon, Dan Mates, and Steve Toth of BLM for support in software testing, Scot MacDonald of the University of Maine for contributions to the software development, and the support of other CTAG members Bernard Hostrop, Tom Noble, and Tom Wohlwend.
Blanchard, B.M. (1990), Utility Program Development: A Digitally Integrated Measurement Management System for the U.S. Public Land Survey System, M.S. thesis, University of Maine, Orono, ME, 86 p.
Hintz, R.J., Blackham, W.J., Dana, B.M., and J.M. Kang (1988), Least Squares Analysis in Temporal Coordinate and Measurement Management, Surveying and Mapping, Vol. 48, No. 3, pp. 173-183.
Hintz, R.J. and C.J. Rodine (1990), Automation and Precision in a Cadastral Surveying Environment, Proceedings of the ACSM-ASPRS Annual Convention, pp. 124- 133.
Hintz, R.J. and H.J. Onsrud (1990), Upgrading Real Property Information in a GIS, URISA, Vol. 2, No. 1, pp. 2-10.
U.S. Dept. of Interior, Bureau of Land Management (1973), Manual of Instructions for the Survey of the Public Lands of the United States 1973, U.S. Government Printing Office, 333p.
Wahl, J.L. (1990), Cadastral Measurement Management User's Manual (Beta Release), unpublished, 120p.
Wahl, J.L., Rodine, C.J., and R.J. Hintz (1991), Development of Electronic Field Book for Cadastral Retracement Surveys, Proceedings of the ACSM-ASPRS Annual Convention, accepted for publication.
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