THE USE OF A PDET FOR SURVEY DATA COLLECTION

R. Kok

Agricultural Engineering Department, Macdonald Campus ofMcGill University 21J11 Lakeshore Blvd. Ste. Annede Bellevue, Quebec H9X ICO

Received 20 September 1982, accepted 28 January 1983

Kok, R. 1983. The use of a PDET for survey data collection. Can. Agric. Eng. 25: 29-32.

During the past 6 years a computer-based surveying/ mapping/ drainage design system has been developed. Thissystem allows data entry from a wide variety of sources such as the Automated Surveyor, PDETs (Portable data entryterminals) and standard peripherals such as card readers, tape drives and keyboard terminals. Survey data and otherrelevantinformation may thereforebe collectedmanually or by anyother, moresophisticated means. As part of a systemperformance test, a PDET (Norand NT5) was evaluated in termsof its usefulness and dependability in the field duringsurvey data collection. Although some drawbacks were noticed in the use of this technology as compared with therecording of data in the traditional field notebook, considerable time savings do result from it. Data are manuallymanipulated only once, upon entry. This reduces the number of resultant errors. An adequate archiving system wasfound to be an absolute necessity.

INTRODUCTION

The collection, recording and transmission of data is of great concern to all thoseinvolved in surveying, as well as to manyothers. Traditionally, in surveying, dataare written down in a field notebook. In

essence, this means that the data availablefrom the instrument are collected and im

mediately recorded on a storage mediumby a human operator. It is then transmitted(i.e. the notebook is transported) and retrieved from storage, again by a humanoperator, and processed. When comparedto modern, electronic methods, traditionaldata handling has some advantages. System malfunctions (e.g. faulty instrument,4'unreasonable" data, etc.) are quicklydetected. Once the data are recorded, theyare relatively safe unless the storage medium itself is lost in toto. If, during laterprocessing, some data seem'' suspicious,''a ''backup copy" stored in the operator'sbraincan be readily accessed. Frequently,by referring to extra ' 'implicit information" resident in the operator (i.e. a three-dimensional memory of the land topography) data interpretation problems can beresolved without having to return to thesurvey site. This extra information is usedmost extensively if the instrument operator is also the person who processes thedata, e.g. if it is the surveyor who drawsthe map. In the traditional method, dataaccuracy may suffer as the result of errorsmade during transmission, recording andretrieval. Some of these errors may, however, be correctable by reference to humanreasoning and memory. In data handlingby biological machines low quality hardware performance is compensated for bythe high quality of the software. In the useof humans in these activities the maindrawbackis their low operating speed andhence their high cost per data point.

Compared to biological systems,"imitation brains" (i.e. computers) havebut tiny memories. Their performance is,however, more predictable and they aremore precise. A computer-based surveying system such as the microprocessor-controlled, completely automated surveying instrument described by Kok et al.(1978) can be very accurate since hardware can be designed to operate at any required performance level. It can collect,record, retrieve and transmit data considerably faster than a human. It can also efficiently transfer data to computing equipment which may automatically process it.Such a system does, however, not havethe software sophisticationof a biologicalmachine so that malfunctions are not aseasily detected and identified. Enough"explicit data" must be collected to define all required aspects of a survey sitesince no "implicit information" gatheringtakes place.

Data are much less safely stored on amagnetic medium or in a semiconductormemory than when they are written onpaper. To lose written data one must losethe whole field notebook; to lose bits orbytes any number of catastrophic techniques may be (and have been) used. Automated data handling may be very advantageous as compared to the use ofhumans, in terms of cost as well as easeand speed of operation, if the followingthree principles are adhered to: (1) the limitations of the system, especially its minimal intelligence, must be kept in mind indefining and structuring the system task;(2) the system must be designed to compensate as much as possible for the relatively low quality software and to take advantage of the high dependability of thehardware; this usually implies that systemflexibility will be severely limited, as

CANADIANAGRICULTURAL ENGINEERING, VOL. 25, NO. 1, SUMMER 1983

compared to the flexibility of a human;and (3) data processing software should bedesigned to allow for human input to makeup for system shortcomings and inflexibility.

Although a design for a fully automatedsurveying system was published by Koket al. (1978), no such systems are for sale.Semi automatic systems, such as the Hewlett Packard "total station" and equivalents, which measure distances and anglesand record these on a data tape, are commercially available but are expensive($15 000 and up). They are also somewhat cumbersome to use since for each

shot the instrument must be preciselypointed at a corner prism mounted on topof a rod. The allowable prism movementand hence the length of this rod areseverely limited. Under appropriate circumstances this technique yields data ofexceptionally good quality and accuracyat a relatively high cost.

A viable alternative to both the acquisition of expensive machinery and the extensive use of human labor lies in the useof a portable data entry terminal (PDET).Some of the advantages (and disadvantages) of both the former methods arethereby gained. In this project it allowedthe use of conventional equipment (levelor transit with rods) and a simplified surveying technique (described by Kok et al.1978) structured to be used by first yearuniversity students. This system producesdata which are particularly suitable for automaticprocessing. Data were mostly collected by a crew of four: two rod men, oneinstrument operator and one person entering the data into the PDET; crews of twoor three have also been used. The PDETapproach has the disadvantage that humanlabor is used to collect and record data, sothat errors may be introduced in these

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steps. Data are, however, handled by humans only once so that the time investment is minimized. Once entered into the

PDET, data can be transferred easily toother storage devices and to processingequipment. Since the PDET is essentiallybeing employed as an electronic fieldnotebook, the human still collects extra4implicit information'' and can contributefrom this, if the processing software is capable of accepting such input.

PDETs are in sophistication intermediate to manual and fully automated systems. In selected circumstances their utilization results in a lower cost than eitherof the other two approaches. This technology is applicable in surveying as wellas in other data collection activities. Some

aspects of the equipment available and ouroperating experience with a PDET in asurveying project are described in thispaper.

EQUIPMENT AVAILABLEA PDET is a portable electronic device

into which data can be entered. Usuallythe PDET also stores such data althoughin some instances it may transmit themdirectly. The "portability" of these devices is at times questionable since someobtain their power from a 12-V DC leadacid car battery; others require a 115-VAC power source. Some PDETs constitute an integral part of a larger equipmentassembly such as a distomat.

In this paper, the term PDET refers tobattery powered, truly portable (i.e. lessthan 5 kg) devices which are specificallydesigned for data collection. They musttherefore accept, store and retransmitdata. They may be divided into classesaccording to several criteria: storage medium, data input type and intelligencelevel.

PDET storage media commonly employed are magnetic tape and semiconductor memory. On the former, data arestored sequentially; in the latter, data areaccessible randomly. Having random access to data after entry can be advantageous although it can also cause confusion; "correcting" erroneous data in thefield frequently worsens the problem. Bymeans of installing appropriate softwarein the PDET, tape can also be made toappearas randomaccessand semiconductor memory as sequential storage. Tapehas the advantage that data can easily bephysically removed from the PDET andplaced in a vault for safekeeping. Semiconductor memory does not require abulky, expensive, power-consuming andheavy mechanical tape drive. It is, however, very easy to accidentally wipe the

30

memory clean of painstakingly acquireddata.

Most PDETs have numeric keypadswith keys for numbers and some specialcharacters and functions. As is commonlydone with electronic calculators, severalsymbols may be assigned to each key. Thespecific meaning of a key entry can thenbe selected by means of a special functionsequence. In this manner complete alphanumeric capability may be available tothe user through a relatively limited number of keys. This approach may suffice inprogramming electronic calculators but isnot very convenient in routine data entry.Most PDETs are designed to collect onlynumeric data. Some truly portable, fullkeyboard microcomputers do exist. Thesemay also be used as PDETs with alphanumeric capability. PDETs are also available which can accept analog and digitallyencoded signals together with keyboard-entered input.

PDETs presently for sale may be categorized as dumb, semi-smart or smart. Adumb PDET must minimally be able toaccept data, store, retrieve and transmitthem. Any of these functions may be carried out either by discrete, readily identifiable hardware units (e.g. cassette taperecorder) or by software. Semi-smartPDETs have a much wider range of capabilities. It may be possible to "download" instructions or other information totheir memories from a host computer sothat, for example, during data entry theuser might be shown a prompting messageto remind him of what needs to be enterednext. At this intelligence level data reviewand editing capabilities are also usuallyavailable; data formats are often flexible.Smart PDETs are fully programmablemicrocomputers specifically designed fordata collection. They can perform all thefunctions described above but operate under programcontrolas well. They can beused for automatic data logging, in-fielddata checking, initial data processing andpreliminary report writing. Programsmight be entered on the PDET's keyboard, be downloaded from a host or bepermanently resident as firmware. Cheap,smart PDETs containing a PROM chipprogrammed for a specific data collectionfunction will soon be commercially available. The advantages of such a machineover user-programmable PDETs will be(1) the user will no longer be required toprogram, this will make the technologyaccessible to many more consumers and;(2) it will become very difficult to makeerrors. The machine will remain completely flexible; the user will be able toadapt his PDET to a new function simply

by having a different PROM chip installed. We are presently developing sucha smart PDET, specifically oriented to operate with the surveying/mapping/drainage design system.

METHODS AND EQUIPMENT USEDTo test the surveying/mapping system

described by Kok et al. (1978), Murphyet al. (1979), Kok and Begin (1981) andKok et al. (1981), a total of 261 ha wassurveyed during the summer of 1981. The -land surveyed constitutes all the farmlandlocated on the Macdonald Campus Farmof McGill University. The area was subdivided into 58 parcels, ranging from 0.4ha to 12.4 ha. These parcels correspondto the fields into which the farm is presently divided. Individual land parcel sizesare shown in Table I. Some land parcelswere surveyed with a transit, others witha level. The type of survey used (L or T)was determined by the land class. This isindicated in Table I. Survey data were recorded using a Norand NT5 PDET.When a survey crew of four was used itconsisted of two rodmen, one instrumentoperator and a PDET operator; in a crewof two, one person was rodman while theother operated both the instrument and thePDET. Survey crew size depended on theavailability of personnel on any given day.

The Norand NT5 is a PDET which usesmagnetictape as its storagemedium. Eachtape can hold about 145 000 characters(10 000 surveying records). This machinewas designed for stock taking in supermarkets, large drugstores etc. It was therefore not waterproof and could be used onlyduring fair weather. The NT5 consists ofthree units: a hand-held key entry unit, aportable tape recorder and a control unit.Only the key entry unit and the tape recorder are taken into the field where theyare interconnected with a cable. The control unit remains in the office. It containsthe transmission and battery charging circuitry. The NT5 could operate for a fullday (10 h) on its rechargeable batteries.The transmission circuitry was considerably modified to electronically integrateit with the rest of the equipment. The NT5has a pad of 16 keys, corresponding to thenumbers 0 to 9, *'start," "stop," "enter," "clear," "minus" and "blank." Ithas an LED display of 12 characters. Thisis also its record length. For level surveys,one record was entered per data point (onedigit for field code, three each for lowerand upper stadia, five for horizontal angle); for transit surveys, two were entered(digits as above, plus five in the secondrecord for vertical angle).

The NT5 is a totally dumb terminal.

CANADIAN AGRICULTURAL ENGINEERING, VOL. 25, NO. 1, SUMMER 1983

TABLE I. LAND PARCEL SIZES AND SURVEY RESULTS

Variable numbert Variable numbert

1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8

LODS02 L 4 8.8 141 22 16 2.5 MAC028 L 4 8.4 178 12 21 1.4

LODS04 L 4 5.3 189 20 36 3.8 MAC030 L 2 3.1 107 8 35 2.6

LODS06 L 4 12.1 171 20 14 1.7 MAC031 L 4 4.0 86 6 22 1.5

LODS08 L 4 3.3 126 6 38 1.8 MAC032 L 2 4.0 97 7 24 1.8

LODS09 L 4 1.7 66 8 39 1.7 MAC034 L 4 5.4 156 16 29 3.0

LODS10 L 4 4.2 145 14 35 3.3 MAC036 L 2 2.0 41 4 21 2.0

LODS12 T 2 2.3 98 5 43 2.2 MAC038 L 4 2.2 64 4 29 1.8

LODS14 T 4 3.7 68 6 18 1.6 MAC040 L 4 9.8 215 20 22 2.0

LODS18 L 4 10.8 311 22 29 2.0 MAC042 L 4 4.7 93 12 20 2.6

LODS20 L 4 0.9 27 14 30 15.6 MAC044 L 4 6.5 109 9 17 1.4

LODS22 L 4 3.6 77 10 21 2.8 MAC046 L 2 3.5 62 4 18 1.1

LODS24 L 4 3.0 86 8 29 2.7 MAC048 T 2 4.0 75 6 19 1.5

LODS26 L 4 1.3 49 4 38 3.1 MAC050 L 4 4.3 91 6 21 1.4

MAC002 L 2 2.2 73 6 33 2.7 MAC052 T 4 4.6 102 10 22 2.2

MAC004 L 2 7.3 196 11 27 1.5 MAC053 T 4 2.0 85 X 43 4.0

MAC006 L 4 12.4 240 26 19 2.1 MAC054 L 4 0.4 32 2 80 5.0

MAC008 L 2 6.9 110 7 16 1.0 MAC055 L 4 10.8 172 26 16 2.4

MAC009 L 2 2.5 77 5 31 2.0 MAC056 L 2 0.7 42 4 60 5.7

MAC010 L 4 3.7 82 12 22 3.2 MAC057 L 4 1.9 45 2 24 1.1

MAC012 L 4 1.8 61 4 34 2.2 MAC059 L 4 4.8 109 10 23 2.1

MAC014 L 2 3.4 97 7 29 2.1 MAC060 L 4 3.8 93 8 24 2.1

MAC016 L 2 3.6 73 7 20 1.9 MAC062 L 4 6.1 143 12 23 2.0

MAC017 L 2 3.3 83 9 25 1.7 MAC064 T 4 7.0 128 18 18 2.6

MAC018 L 2 4.4 109 8 25 1.8 MAC066 L 2 4.8 105 5 22 1.0

MAC019 L 2 2.9 82 6 28 2.1 MAC068 L 4 2.1 41 4 20 1.9

MAC020 L 2 5.2 128 8 25 1.5 MAC070 T 4 4.2 72 8 17 1.9

MAC022 L 2 5.9 171 10 29 1.7 MAC074 L 4 5.2 121 10 23 1.9MAC024 L 2 6.9 166 12 24 1.7 MAC075 L 4 0.9 32 2 36 2.2

MAC026 L 2 4.8 93 4 19 0.8 MAC076 T 4 2.0 44 8 22 4.0

tVariable numbers have the following definitions: 1, field name; 2, survey type (L = level, T = transit);3, survey crew size;4, land parcel area (ha); 5, numberof data points taken on land parcel; 6, numberofsurveying manhours (h); 7, numberof data pointstakenper hectare(pt/ha);8, numberof surveyingmanhoursper hectare (h/ha).

of sets 0,1,2 and 3 were not significantlydifferent from each other at the 0.05 level

or even at the 0.20 probability level. Set4 was not included in the analysis since itonly had two members. Similarly, the setsdid not differ in terms of the average number of data taken per hectare. Although it

is tempting to conclude from the averagevalues of surveying manhours per unitarea reported in Table II that crews of twohave a higher productivity than crews offour, these averages for sets 0, 1, 2 and3 were found not to be significantly different at the 0.05 or 0.10 probability level;the averages for sets 1 and 2 become significantly different only at the 0.13 levelin this respect. When the combined datafrom sets 1 and 3 (crew size = 4) are compared with those of sets 2 and 4 (crew size= 2), average values of survey crew timeper hectare of 2.8 and 2.0, respectively,are obtained. These are then significantlydifferent at the 0.07 level but not at the

0.05 probability level. It may thus be concluded that with the surveying techniqueand methodology used, two-person crewsare probably more productive than four-person crews.

Significant correlation coefficients (atthe 0.01 probability level) were found between field size and number of data pointsper unit area and between field size andsurvey crew time per unit area for sets 0,1 and 2. Although correlation coefficientsof similar magnitude were found for set 3,these were not significant at either the0.01 or 0.05 probability level. The valuesof the correlation coefficients are given inTable III. In all instances, when the fieldsize increased, the number of data pointstaken per unit area and the survey crewtime required per unit area decreased.Usually, for the larger fields relativelyfewer boundary points were shot. Often,the larger fields also were the more evenones, containing few topographic anomalies.

Data cannot be edited once entered but can

be viewed by rewinding the tape and playing it forward. Data entry can also be resumed again after this. One field code wasreserved as a flag to the processing software to indicate the previous recordshould be deleted from the file.

RESULTS

The number of data points taken and thenumber of manhours spent by the surveycrew are reported for each field in TableI. The field areas were found by means ofa planimeter. The number of data pointstaken per unit area and survey crew man-hours spent per unit area were calculatedfrom the data. These are also shown inTable I.

The surveys were broken down into fivesets, according to two criteria: (1) the typeof instrument used and (2) the size of thesurvey crew. Two ranks were used foreach (L and T for survey type, 2 and 4 forcrew size), dividing the data into four sets(1 to 4). The fifth set (0) consisted of allsurvey data combined. The set averages,standard deviations and coefficients ofvariation are shown in Table II for eachof the following: field size, number of datapoints per unit area and survey crew man-hours per unit area. The average field sizes

TABLE II. AVERAGES AND STANDARD DEVIATIONS OF VARIABLESt

Survey Crew Number Standard CoefficientSet type size of fields Average deviation of variation

Variable field size (ha)0 L&T 2&4 58 4.5 2.8 0.621 L 4 31 5.0 3.4 0.692 L 2 19 4.1 1.8 0.443 T 4 6 3.9 1.9 0.484 T 2 2 3.2 1.2 0.38

Variable: numberof data points per unit area (no./ha)0 L&T 2&4 58 27 11 0.411 L 4 31 27 12 0.442 L 2 19 27 9 0.353 T 4 6 23 10 0.42

4 T 2 2 31 17 0.55

Variable: number of surveying manhoursper unit area (h/ha)0 L&T 2&4 58 2.5 2.0 0.801 L 4 31 2.8 2.5 0.902 1. 2 19 2.0 l.l 0.533 T 4 6 2.7 1.0 0.394 T 2 2 1.8 0.5 0.26

tValues of these variables were determined on a field-by-field basis, then used in further calculations.

CANADIAN AGRICULTURAL ENGINEERING, VOL. 25, NO. 1, SUMMER 1983

TABLE III. CORRELATION COEFFICIENTS

Set

number

Field size

and data perhectare

Field size

and crew time

per hectare

-0.514

-0.541

-0.539

-0.319

-0.317

-0.664

DISCUSSION

During a complete summer survey datawere successfully recorded on the NT5and retrieved again. On only one occasionwere data lost. This was caused by a faultycable connection between the entry unitand the tape recorder. The secure physicalattachment of any such cable to both unitsis a necessity for a dependable PDET. Survey crew time spent per hectare was in anacceptable range, indicating that both thesurveying system and the recordingmethod are functioning properly. Thegreat advantage of the method lies in thesurvey data being available in a formatready for transmission and processing ina minimum of time.

Although the Norand NT5 was far frombeing the perfect PDET, it sufficed andallowed the acquisition of valuable fieldoperating experience. Based on this, a setof design objectives for a firmware-controlled "ideal PDET" for the surveyingsystem has been developed. DesirablePDET attributes have been divided into

two categories: physical and cognitive.

PDET DESIGN OBJECTIVESThe ideal PDET should weigh about 1

kg so that when it is carried its weight isperceptible but not burdensome. To makeit comfortably hand-held it should beabout 10 cm wide, 15 cm long and 2 cmthick. The keys should be large enoughand spaced far enough apart so that whenthe operator wears thick gloves PDET useis not impeded or complicated. The PDETmust be as resistant to physical abuse asthe traditional field notebook; it must bequite indestructable if it is to withstand thevigors of the agricultural summer surveycrew. A pad of 16 keys will give adequateinput flexibility; a 24-character, three-rowdisplay will be sufficient for output. Thisdisplay must be clearly legible in brightsunshine as well as under low light conditions. The PDET must contain its ownpower source capable of energizing it forup to 24 h. The physical requirements out

lined above may eliminate the use of tapeas a recording medium. If semiconductormemory must be used, a facility should bereadily available to the user to copy thecontents onto a backup tape before transmission to a host computer.

The PDET memory capacity should besufficient to hold 3 days of accumulatedsurvey data. A 32K memory of 8-bit byteswill therefore be ample. The data storedtherein should be accessible to the operator for review but it should not be possibleto modify them once they are entered. Instead, the operator should be able to markany data record during a review so as tocall attention to it during later processing.To facilitate data access during a review,the memory should be organized intopages.

The PDET operating system wouldprobably be supplied as firmware on aPROM chip. The operating system mustbe structured to anticipate and effectivelydeal with human error, machine failureand accidents. A preliminary analysis ofthe data should be carried out upon theirentry and the data rejected if an error isfound (e.g. angle greater than 360°, fieldcode not possible). An audible alarm anda blinkingdisplay, combinedwith simple,clear messages, might be used to bring anerror condition to the attention of the operator. The operating system must alsoperform a number of housekeeping functions and make available such informationas the amount of memory remaining, etc.It should be very easy to learn how to operate the PDET; the maximum learningtime should be 1 h (first year engineeringundergraduate). The PDET should becompatible with standard transmissionand computing hardware such as acousticcoupling equipment and be able to transmit over voice grade telephone lines.

If, as the result of machine failure or aserious mishap, the PDET ceases to function, the memory should be fully protected. In this regard, magnetic tape as amemory device is the most flexible and

dependable since it can even be mendedafter it breaks. Semiconductor memories

are frequently backed up with small, independent batteries so that data are not lostif the main batteries run down and need

to be replaced. Several types of nonvolatile chip memory are also under development. These will not require any energywhatsoever to retain their contents so that

even a complete power loss would not destroy data. Some advantages of both semiconductor and tape memory are thus combined. Their use may be the mostacceptable compromise solution. Dataprotection and safeguarding must be considered very seriously if PDET technologyis to become generally accepted.

CONCLUSIONS

Although some drawbacks were noticedin the use of PDET technology in surveying, considerable advantages also resulted. Further PDET development couldimprove the efficacy of the data collection, recording and transmission system.The ideal PDET must have all the goodqualities of the field notebook and none ofits negative aspects; it must be a real improvement over the status quo and not justa change from it. By properly designinga specific-task-oriented, intelligent PDETthis goal can be achieved.

ACKNOWLEDGMENT

The author gratefully acknowledges the financial assistance of the Conseil de Rechercheset Services Agricoles du Quebec.

REFERENCES

KOK, R., R. LANGLOIS, E. R. NORRIS,and R. S. BROUGHTON. 1978. An auto

mated topographic survey method suitablefor use in drainage work — a design concept. Trans. ASAE (Am. Soc. Agric. Eng.)21(5): 931-936.

KOK, R. and J. BEGIN. 1981. Evaluation ofautomatic contouring methods for drainagedesign. Trans. ASAE (Am. Soc. Agric.Eng.) 24(1): 87-96.

KOK, R., S. T. CHIENG, and R. S.BROUGHTON. 1981. A software packagefor agricultural drainage design. Proceedings of the 2nd International Conference onEngineering Software. Imperial College,March 1981. R. A. Adey, ed. pp. 626-641.

MURPHY, R. C, R. S. BROUGHTON, andR. KOK. 1979. Computer-aided plotting oftopographic survey data. Can. Agric. Eng.21(1): 31-37.

32 CANADIAN AGRICULTURAL ENGINEERING, VOL. 25, NO. 1, SUMMER 1983