'ÿþM' by ÿþA - Page 1 of 10

SCIENCE AND TECHNOLOGY AID OUR MAP MAKERS

J. D. LINES

Assistant Director, Division of National Mapping

Reprinted from the National Development Quarterly, September and December,

1969

Accurate maps have long been recognised as a basic requirement in the detection,

assessment and development of natural resources. A mineral prospector pegging a claim -

engineers designing and developing mines, roads, railways, ports and irrigation schemes -

surveyors setting out a new town. They all use maps.

Simply put, the map maker is called on to provide accurate "pictures - of particular areas

- or an entire country. He must show natural and man-made features in their correct

geographic positions and put in contours showing the true height of the land above sea

level. His "pictures" are topographic maps. The modern-age demand on him is for greater

and greater precision coupled with fast production.

The map maker has, therefore, sought scientific and technological help to replace tedious,

arduous and, at times, dangerous methods of survey and observation previously carried

out entirely by ground teams.

Permanent steel survey beacon at a station in a remote part of central Australia. The

helicopter is about to pick up a survey party and items of equipment flown in earlier.

Prior to the advent of aerial photography the earliest maps had been produced with the

aid of magnetic compass and tape, and in outback Australia sometimes by compass and

the measured tread of camels to determine distance travelled. Further instrumentation

was introduced and then came aerial photography.

Aerial photography was introduced to Australia in the early 1930's but was not used to

any great extent until World War II experience demonstrated its innumerable uses.

In the immediate post-war years, Australia moved to set up a national mapping

organisation - now the Division of National Mapping of the Department of National

Development,(1) and it was decided then to base all future topographic mapping on the

wealth of information which could be gathered relatively quickly from aerial photography.

A systematic programme was planned to cover the continent by overlapping photography,

each 9 in x 9 in photograph showing an area of approximately 50 square miles. (Later

equipment increased the coverage to about 140 square miles for each photograph.)

A pre-requisite to the use of photographs was the establishment of thousands of control

points which would permit map makers to fix the exact position of each photograph on the

face of the continent, and ensure that maps produced at a later stage would fit together

accurately to form a complete picture of the continent.

A primary set of points was established across Australia under a programme known

among surveyors and scientists as a geodetic survey. Such surveys had been carried out

in earlier years by State authorities and Army Survey, covering only relatively small areas.

The requirements of the national mapping programme, however, required a national

geodetic survey and this resulted not only in the complete coverage of the continent by

1966 but far greater accuracy than had been previously achieved. Further survey work is

now being undertaken to fill in open spaces between sections of the primary geodetic

survey and provide marks to fix the positions of aerial photographs.

Probably the greatest advance in modern surveying came in the mid1950's when

electronic instruments were developed to measure distances on the ground. This gave rise

to a new term, EDM - electronic distance measuring. This became the modern surveyor's

tape, and unlike any previous tape in that distances from a few metres to more than 50

miles could be measured at once to a few centimetres in accuracy.

Left: Perspective drawing shows how "Aerodist"

equipment in an aircraft is used to measure the

distance between two survey points.

Above: White concrete survey mark set by National

Mapping surveyors in western New South Wales.

The steel guide posts assist ground parties to locate the marker.

EDM quickly extended from ground equipment to airborne methods and is now installed in

satellites to take measurements across oceans. (Modern mapping makes extensive use of

the metric system of measurements so that the complications of feet and inches, chains

and links - odd mixtures of dozens and tens - are on the decline.)

EDM is used quite extensively in Australia to measure distances on the ground to assist in

establishing the geographical co-ordinates of survey stations which in turn are used to

position aerial photography. Geographical co-ordinates are simply latitude and longitude.

Ground measurements are restricted to "line of sight" conditions. As much of this country

is relatively flat, traversing large sections of open spaces necessitates more

measurements than would be required if the terminals of lines were more elevated and

lines correspondingly longer. These conditions are artificially produced by use of aircraft.

An airborne system used more in Australia than anywhere else in the world, and called

"Aerodist", measures long lines in two parts, that is to one ground station from an aircraft

while simultaneously measuring from the aircraft to a second station.

Left: "Aerodist" equipment installed by the

Division of National Mapping in a chartered

Grand Commander aircraft.

From a series of three simultaneous

measurements which show when the

aircraft is directly between two ground

stations, the actual ground distance

between them can be calculated. Lines up

to 200 miles long have been calculated in

this way to an accuracy of one or two

metres. This system permits a geometric

pattern to be built up over the open

spaces, and mathematically adjusted to

the basic geodetic survey with the aid of

electronic computers.

Helicopters save time for the surveyors

by placing ground station men and

equipment exactly in desired locations

when ground transport would be

impracticable.

In desert operations, the planning of this

work requires more than usual care as

ground station parties are heavily

dependent on the continued service of a

helicopter.

In addition to the acquisition of geographical co-ordinates, the third ingredient required

from field surveys is a number of spot heights accurately related to sea level. These

heights provide the starting points and the necessary checks for contouring from aerial

photography.

Once again, EDM is the technique to speed up the work and enable operations to proceed

virtually irrespective of terrain.

The Division of National Mapping uses airborne profile recording (APR) techniques very

largely for this work.

The present equipment, obtained on contract, employs the radar principle to measure the

distance (height) between the aircraft, which flies at a constant elevation, and the terrain

below.

The heights are recorded on moving charts as continuous longitudinal sections, and

aircraft position is obtained by continuous vertical photographs of the terrain. From check

measurements of the aircraft over surfaces of known elevation, and other corrections,

heights can be deduced for selected points on the ground.

A further development of this technique is being undertaken at the request of the Division

by the Weapons Research Establishment of the Commonwealth Department of Supply.

Composite illustration shows a profile measured by a laser terrain recorder from an aircraft.

This employs the pencil beam of a laser light source, which, unlike a radar-type

transmission, can be contained to a cylinder of about 2 ft diameter at ground level from

an operating altitude of 7,000 ft. The modulated laser transmission is another form of

EDM, and because of its great pointing accuracy and sensitivity to change of distance,

provides a new and more accurate approach to establishing ground elevations from the

air.

The Australian laser terrain profiling equipment has already been successfully flight tested

as a prototype.

In its completed form, it will be the first laser profiling equipment in the world constructed

specifically for surveying purposes. It will employ many sophisticated ancillary techniques,

and safe operation is a feature of its design. The low power level of the transmission will

not be a hazard to persons or property.

The Division employs an unusual vehicle to supplement the ground heighting programme.

This is the Johnson Ground Elevation Meter which looks rather like a station sedan at first

glance. Closer inspection reveals that it has five road wheels, four-wheel drive, four-wheel

steering (so that the rear wheels track exactly with the front wheels), air-conditioning,

automatic tyre pressure control and a large array of electronic equipment.

Left: National Mapping vehicle

equipped with a Johnson

Ground Elevation Meter.

The two quantities required

to calculate the difference in

height as the vehicle travels

up and down gradients (that

is the distance run and the

angles of the gradients) are

determined respectively by

the fifth wheel, and an

electro-magnetic pendulum

situated on a bar joining the

front and rear axles of the

vehicle, which is the plane of

reference. As this bar changes attitude, the deflection angles from a horizontal plane are

continuously computed from signals received from the pendulum.

The calculations of difference in height during travel are made electronically and recorded

in numerical form on a paper tape.

This is yet another form of EDM and produces results with an error less than 10 feet in 50

miles at 15 miles an hour on reasonably good road surfaces. This equipment is not

suitable for cross country travel.

The methods and equipment discussed in this article have been adopted to speed up and

improve the gathering of knowledge and measurements required by photogrammetrists

who convert the aerial photographs into manuscript maps which are then finally drawn by

cartographers as maps suitable for ultimate reproduction by lithographic printing

processes. This kind of map, a line map, is likely to be produced and used widely for many

years yet, but for some purposes it could be replaced by a form of map produced very

quickly by re-processing aerial photographs into "ortho-photos" produced by equipment

which is the closest thing yet to a "map making machine".

Photographs for the national mapping programme are taken from aircraft flying high east

to west and covering strips of 100 miles. The photographs in each strip overlap each other

by at least 60 per cent and each strip is designed to overlap its neighbour on each side by

25 per cent.

This pattern of flying provides near vertical photographic material for three-dimensional

(stereoscopic) viewing of the terrain. The cameras used possess precise qualities of lens

and mechanism and they are calibrated by the National Standards Laboratory of the

CSIRO in Sydney so that their geometrical properties are known accurately to a few

microns - thousandths of a millimetre.

To match these qualities, dimensionally stable photographic film is used and processed

under strict production conditions. Accuracy is vital because there is an image of about

140 square miles of country on each 9 in x 9 in frame of a roll film.

The subsequent processes in map preparation are based on positive transparencies

reproduced from the original negatives - again on dimensionally stable film.

These are made in equipment which not only produces an even-toned image by electronic

scanning, but at the same time removes the distortion in the original image attributed to

curvature of the earth.

After ground control points have been fixed in predetermined positions on a small

percentage of the photographs, the control data are used in graphical or mathematical

processes to derive further control points on each individual photograph.

These processes, which give substantial economies in the density of ground control

required, rely on extremely accurate measurements taken from aerial photographs and

are an important segment of the branch of surveying known as photogrammetry. This is

the science of taking accurate measurements from photographs.

An overlapping pair of transparencies is then introduced into a stereoscopic plotter in

which can be seen a stereoscopic model. Map makers know the apparatus as a "stereo-

plotter" and the model as a "stereo-model".

Left: A manual stereo-

plotter in the Division of

National Mapping,

Melbourne. The two

transparencies are

mounted in the carriers

under the shaded lamps

and the stereo-model is

viewed through the

eyepieces immediately in

front of the operator.

The "floating" mark is

moved by the control in

the operator's hand and

contour lines are

reproduced on the table

at bottom right.

A stereo-model is not a

model in tangible

three-dimensional

form, but an optical

illusion seen by the

plotter operator as he looks through a dual eyepiece at the overlapping pair of

transparencies.

The operator really has a bird's eye view of a piece of country without actually being

there. He is able to see clearly natural and man-made features and is thus enabled to

ensure that they are shown accurately on maps prepared for printing.

All the hills and valleys can be seen clearly and this facilitates contouring. The operator

can control a pointer built into the viewing system and as he moves this along points of

equal elevation a slave arm (or pantograph) records the contour line on a table to one

side of the apparatus.

For the past 20 years the optical- mechanical system of plotting from aerial photographs,

or stereo-photogrammetry, has been considered a tremendous advance on the previously

more laborious and less accurate methods of map making.

Left: Contour lines and elevation points

reproduced by an automatic stereo-

plotter.

The next 20 years should see an

equally impressive revolution in the

production of maps due to the

inevitable widespread introduction of

automation in photogrammetry.

Already Australia has felt the impact of

automation - the Division of National

Mapping introduced an automated

stereo-plotter in 1968.

This is still the only such piece of

equipment in this country and one of

the few operating on a day- to-day

basis in the world.

The equipment is a product of Swiss

and American research and like much

other modern surveying equipment it

makes extensive use of electronics.

In essence, it is a stereo-plotter which

still requires basic information derived

from ground surveys and in which a

pair of overlapping transparencies

need to be set up and adjusted with some human aid.

The operator of a manual stereo-plotter looks into the machine and produces original copy

for maps, showing contours and features such as roads and rivers by lines and smaller

individual features by symbols.

With an automatic plotter nobody needs to look into the machine - after the initial

adjustment - as it automatically produces orthophotographs and contours.

An orthophotograph is a true-to-scale plan of the terrain, reproducing with surprising

fidelity the features which can be observed on an untreated aerial photograph. An

ordinary aerial photograph contains distortions primarily due to variation in the height of

the terrain but due also to small tilts of the camera as each negative is exposed.

The transition to an orthophotograph with the simultaneous collection of contour

information is the nearest thing so far achieved to a map-making machine, for the ortho-

photograph will complement - and may for many purposes supersede - the line map as we

now know it.

Put together in mosaic form, these corrected photographs form a new map product - the

orthophotomap.

The automatic stereo-plotter presently in use relies on an electronic scanning system

similar to a television camera to observe the original transparencies and it reproduces the

images corrected for height displacement and tilt on a film enclosed in the machine.

Automatic stereo-plotter, showing the control cabinet (right), digitizing equipment

(left/front) and tape deck (left/background).

The machine can be set so that as its narrow scanner beam traverses the pair of

overlapping transparencies signals will be transmitted to record steps of 20 metres in the

elevation of the terrain.

The recordings emerge on the orthophoto negative as small segments of a contour line.

The segments are alternately thick and thin, giving positive identification of successive

contour intervals.

Colour film is used to enable the orthophoto detail and contour segments to be recorded

in different colours so that the contour segments can be filtered out for separate

attention.*

Overleaf plate 1 shows an orthophoto with contour segments filtered out, while plate 2

shows a black and white reproduction direct from an orthophoto colour negative. The

separated contour segments are shown on their own in plate 3, but the discontinuities are

not serious. It is quite valid to edit these broken lines into the form shown in plate 4

because they are reproduced at a scale 2.5 times larger than the scale of the map for

which they are intended.

An alternative method of using the automatic stereoplotter for contour work is to set it to

pick up electronic signals at regular intervals as the scanner traverses.

These signals represent latitude, longitude and elevation at a number of points on a grid.

Data on these points are recorded in code on magnetic tape and in effect the equipment

"memorises" the shape of the terrain.

The information on the tape is fed to another type of automatic plotter. This machine

interprets the elevation data and its electronically controlled pen draws complete contour

lines on a sheet of paper designed to overlay an orthophoto.

If required, this equipment will

also put in selected spot elevations

and their heights in figures. An

example of this result is shown in

the illustration above.

This example is at a much larger

scale than usual and shows not

only contours but the values of the

height information from which

contours arc derived.

The grid of heights is suppressed

during production work. The

process is still in the development

stage in the Division of National

Mapping, but it promises

worthwhile economies where

dense contour patterns are

encountered.

Map makers already recognise

orthophotographs as a base for

mapping at scales between 1 to

25,000 and 1 to 100,000 because

they produce a practical map in a

quarter of the time it would take to

produce a traditional line map.

For many other purposes - town

planning, civil engineering and

other work connected with

exploration and development -

they may be expected to have

increasing application.

Since they are capable of

production quickly and in true plan

form, orthophotographs and maps

must be recognised as one of the

basic tools in the hands of men

and women who will plan,

administer and carry out the

development of Australia during

the remaining decades of the 20th

Century.

* Mapping photography for Commonwealth purposes at present is in black and white,

but undoubtedly the problems presently inherent in the use and fidelity of colour film

for every day use will be overcome and there is likely to be more use of this medium

in the future. Colour film in the visible spectrum and in the infra-red area exposed at

relatively low altitudes already has wide acceptance and value for the assessment of

resources data by photo interpretation techniques.

(1)

The Division has taken the central role in a national mapping programme, not only

by contributing a large number of the maps required, but by co-ordinating the work

of the Royal Australian Army Survey Corps and the State Departments of Lands and

Survey in a national mapping effort.

Geoscience Australia's permission to use this material is appreciated and it is acknowledged that this

by permission of the Chief Executive Officer, Geoscience Australia, Canberra, ACT.

Apart from any use as permitted under the Copyright Act 1968, no part may be reproduced by any process

without prior written permission from Geoscience Australia. Requests and inquiries concerning

reproduction and rights should be addressed to the Manager Copyright, Geoscience Australia, GPO Box

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