Airmap as an Aid to Fire and Water Departments
How Overlapping Photographs Are Taken by Airplane to Form Maps—Their Place in the Fire Protection and Water Supply Fields
USE of the airplane in a utilitarian capacity is becoming more and more general. A new development is the combination with it of photography. The following article points out the various purposes in connection with water supply and fire-fighting, to which the aerial photograph can be put. The article suggests many interesting possibilities along this line.
The evolution of the modern airplane contributed largely to the present state of development of aerial surveying and mapping. It is of interest to understand why this should be true and a glance in retrospect will help to clarify some questionable points which may have arisen in the minds of those readers who have become acquainted with this relatively new contribution to the art of map-making. The airplane of today is easily maneuvered and controlled. It is possible to maintain a given altitude, within definite limits and an experienced pilot can fly accurately over a predetermined course. The possibility of maintaining both a given altitude and course led to the adoption of the airplane as a medium in which the aerial camera could be suspended.
Especially Designed Airplane Camera
A specially designed airplane camera is used to take the photographs and is mounted in the observer’s cock-pit. The lens of the camera is pointed vertically downward through a hole in the bottom of the ship. When an exposure is made, a plan view of a section of the earth’s surface is obtained, similar in principle to the usual engineering map with the noticeable addition that all features on the ground are completely detailed. The entire picture is full of information, a positive record of everything that was present at the instant of exposure. Residences, factories, office buildings, parks, undeveloped sections are immediately recognized as such. With a little experience, one may learn a wonderful story from the photographs which are awaiting translation.
It is quite evident that one photograph in itself would not attain the desired results The problem is to determine some method to relate the features shown on overlapping photographs to each other. How these views are obtained will now be discussed.
How Overlapping Pictures Are Obtained
The pilot and camera-man are given duplicate instruction regarding the height from which the photographs are to be taken and the area to be surveyed. When the altimeter registers the predetermined altitude, the pliot maintains this height and the photographer knows that exposures made at this altitude above the earth’s surface will give the desired scale. For example, if a scale of one inch equals four hundred feet is desired, an altitude of eight thousand feet must be maintained with a camera lens whose focal length is twenty inches.
The pilot having reached the required altitude, guides his machine to follow the flight lines which are shown on a map of the area. The photographer is now ready to take his first exposure. The trigger on the camera is released and in the short time of one one-hundredth of a second, one square mile of land is completely surveyed and the notes recorded on a 7-inch x 9-inch sensitized film.
One Photograph Every 25 Seconds
The airplane continues its course while the cameraman operates his instrument releasing the trigger about every twenty-five seconds. The exposure interval is so designed that the successive photographs overlap and a continuous picture of the entire area is thereby obtained. A section of considerable size is mapped with the one hundred exposures on a roll of film and should there be any need for additional exposures, a new roll is easily substituted while in the air.
Prints are made from the exposures and after some necessary calculations they are matched together into a co-ordinated structure, being held in position by means of a special preparation. The completed air map is a step in advance of the conventional line map, preserving its accuracy .but adding completeness of detail which is so useful to municipal investigations.
At the present time, one of the largest cities in the country is having an aerial photographic survey made of the city and its environs. Though this city has a very extensive engineering department, it was found, after prolonged study, that air maps could be used almost universally to good advantage in all of the city departments.
Place of the Air Map in Fire Protection
Fire protection facilities must be thoughtfully worked out in newly developed sections. The proper location of fire houses to adequately cope with a possible conflagration in a residential or business section depends upon the building concentration to the existence of a fire hazard (Figs. 5 and 6.)
In this connection, the recent Berkeley, Calif., fire may be cited as an example. The construction of the section which was destroyed did not follow any general plan but occurred along lines of least resistance. There was need for diagonal streets, street widenings and other similar improvements.
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Airtmap as Aid to Fire and Water Departments
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At a recent convention of the City Managers’ Association the following are some of the fire protection needs to prevent the recurrence of a conflagration :
Mains and feeders sufficiently large and gridironed to give adequate water pressure.
Closer sparing of fire hydrants. (Hydrants are cheaper than fire hose, and furthermore, friction in water mains is far less than friction in fire hose.)
Strict enforcement and aid in enforcement of all ordinances. Then, in addition, proper studies of a district with a view to determining the formation of zoning regulations and construction of fire houses should also be considered.
In most of these recommendations, the study of air maps has been found to materially assist in determining policies to be pursued. Because of the nature of the photographic property, dwellings, factories, improved and unimproved streets are easily identified.
In the case of public hearings, it will be found that these maps appeal more to the layman than the conventional line map with its puzzling, conventional symbols.
Determining Source of Water Supply
The problem of supplying water has long been associated with the primary needs of a community. Just where the source of supply is found varies from back yard wells to the more highly developed mammoth storage reservoirs. With a definite amount of water recpiired per person per day, the problem is a big one. Increases in population signify increases in water consumption. One can mention a number of instances where municipalities had greatly outgrown themselves with the result that the pressing need for water became a vital problem.
The sources of water supply are preferably sought, not along rivers with their attendant dangers of pollution, but in tracts of mountainous country. Investigations are made to determine the possibilities of these tracts as watershed areas and preliminary surveys disclose the quantity of water available in a given year, the size and extent of the reservoir required to impound this amount and the most economical method of delivering the water from the storage reservoir to the city mains.
Study of Watershed Area Through Air Map
Watershed areas can be studied to good advantage with the use of air maps. After elevations have been determined and contours plotted, the area to be submerged is determined. The configuration of the surface will govern the extent of the area. Unimpeachable records of all property which must be condemned to make the development possible are at hand. What this means in the case of legal disputes cannot be overemphasized. For example, when the water has reached its proper level, the property which has been submerged is completely lost to view and examination. There are cases on record wherein property owners made exorbitant claims for damages which could not be disproved. A photograph contains all the evidence desired and a more equitable adjustment of claims is the result.
Once more, the wealth of information furnished, the excellence of the finished product and the form in which it is delivered are factors which contribute to make possible an advantageous study of possible rights-of-way for pipe lines aided by the aerial photographic survey.
Should a preliminary investigation show that a tentative route is undesirable, another may be selected within the bounds of the air map. This is true because the area surveyed photographically is relatively wide in extent, though all details are clearly discernable. In instrumental surveys, a shift in the line would require another examination by a field party. The saving in time and expense between the two methods is quite obvious in this connection.
How Stereoscopic Examinations Are Conducted
Brief mention may be made at this point of stereoscopic aerial photographs. When viewing the ground from high altitudes, the airman observes the country beneath to appear flat. There appears to be a noticeable lack of depth. In this connection, however, stereoscopic views present one of the most valuable developments of aerial photography. Stereoscopic effect is obtained when viewing two photographs of the same object taken from slightly different viewpoints. The usual method of combining the two stereoscopic images is by the use of an instrument called the stereoscope. The photographs are mounted side by side and observed through properly placed surface mirrors. Instead of seeing two photographs, the viewer observes but one image with the addition that all features on this image have been enhanced with a relief effect.
Stereoscopic examinations which are made to determine relative elevations are often used to establish right-of-way lanes. Such features as accessibility during construction and ease of future patrolling are also conveniently studied. Furthermore the wellknown, undesired advertising which is given to any project when surveys are made with transit and level is eliminated in making an aerial survey. It is common knowledge that this enlightenment on the part of the inhabitants has very often caused the failure of a commendable development. The ease with which property sub-divisions are identified and correctly labeled according to ownership has materially aided field men in their transactions.
The accompanying illustrations give an excellent idea of the ease with which ground features are distinguished.
Development of the Aerial Photograph
Before the vertical, or mapping, photographs came into extended use, the oblique aerial view was used to considerable advantage. These air views represent today the peak of perfection in pictorial displays. (Fig. 4.)
Let us trace the evolution to determine, if possible, wherein its chief values exist. In the early days of photography, the ordinary ground view was used in countless ways depending upon the ingenuity of the operator. As an illustration accompanying reports, general municipal information, etc., the ground view was soon recognized as possessing certain valuable characteristics. It showed conditions truthfully and clearly to the general public. The ability to visualize the subject saved the use of otherwise lengthy descriptions which in themselves lost the desired effect.
It soon became evident that in order to increase the usefulness of the photographs for illustrative purposes, it would be an improvement if higher vantage points could be obtained from which to record the view unfolded before the eyes. Accordingly, tops of buildings, towers and other high points were utilized.
The rapid development of the airplane introduced the final step to which the camera platform has been transferred. Seated in the observer’s cock-pit, the camera man grinds away and permanently records the hitherto unappreciated scenes. Highly congested districts, teeming with humanity can be separated from the business zones, the great open spaces which are recognized to be parks, are clearly observed, surrounded by masses of dwellings.
Old familiar scenes are readily recalled and the memory is strengthened because of the ability to visualize all the features at a glance. Oil storage tanks and refineries, factories with smoke-belching chimney protuding upward, congested streets, railroads, wharfs and water-front properties serve to assist the memory in zoning studies and disputes over fire protection facilities and water supply.
Determining Water and Fire Fighting Facilities
In the case of a conflagration both fire and water departments co-operate to prevent further destruction of life and property. Is there a sufficient supply of apparatus and incidental equipment, are the fire plugs conveniently located, can the Yvater supply hold out, where can more be obtained, how can it best be utilized ?
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TURNING IN THE ALARM—How Much Longer Must Cities Depend Upon the Telephone in Reporting Fires? By Yardley.
(Courtesy of Stockton, Cal., Record)
Airmap as Aid to Fire and Water Departments
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To insure the safety of life and property, modern fire prevention methods exemplify the old adage, an ounce of prevention is worth a pound of cure. Careful studies are marie and extensive investigations furnish data for the purpose of minimizing the dangers of fire. It is of much importance to know what conditions constitute fire hazards and as such should be eliminated.
In this respect, the application of air maps and air views, because of their wealth of information are recognized by leading authorities as important complements to municipal investigations.