US 2261201 A
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Nov. 4,1941. R. M. wlLsoN 2,261,201 1 PHOTOALIDADE Filed Oct. 30, 1939 2 Sheets-Sheet l Nov. 4, 19.41.
Filed Oct. 30, 1939 2 Sheets-Sheet 2` SWW , on, in accordance Patented Nov. 4, 1941 PHOTOALIDADE Ronald M. Wilson, Bethesda, Md. Application October 30, 1939, Serial No. 301,961
(Granted under the act of March amended VApril 30, 1928; 370 0. G.
The invention described herein may be manufactured and used by or for the Government of the United States for governmental purposes without the payment to me of any royalty therewith the provisions of the act of April 30, 1928 (ch. 460, 45, Stat. L. 467) This invention relates to means for and methods of making maps or plans from oblique photographs taken from airplanes, airships, elevated camera stations or ground stations, and more particularly to an improved photoalidade and the method of using the same. The use of the photoalidade in photogrammetric surveying is comparable to the use of the well known plane table and telescopic alidade in ordinary ground surveying. l
Instruments and methods already known in the art that are somewhat similar to the instant invention in use and principle are the Bagley photoalidade, described in United States Geological Survey bulletin 657, 88 pp. 1917; the High Oblique Plotter used in Canada (see article by Burns and Field, entitled A Plotter for High Oblique Air Photographs), publislfied in the Canadian Journal of Research, section 'A, vol. 13, pp. 22-35, 1935; and the bulletin entitled Canada Topographical Survey, a graphical method of plotting oblique aerial photographs, 21, pp. Ottawa, 1928; paper presented by R. D. Davidson, entitled A Plotter for Oblique Photographs, in the Proceedings of 29th Annual Meeting of the Canadian Institute of Surveying, held at Ottawa February th and 6th, 1936, published in the Canadian Surveyor, special edition, 1936, pp. 20-2'7; and the instrument designed by Mr. O. M; Miller of the American Geographical Society, described in the article entitled Notes on the construction of the Cape Chidley sheet, appendix l to Forbes, Alexander', A Flight to Cape Chidley, 1935, published in the Geographical Review, vol. 26, No. 1, pp.53-56, 1936.
These instruments have been used for some time to produce maps from oblique photoghaphs without resorting to stereoscopic vision by employing the ordinary surveyors method of intersection for determining the desired location of points.
The Bagley photoalidade uses only'panoramic photographs taken from ground stations, with the camera carefully leveled on a tripod. It is the predecessor of the'photoalidade forming the subject-matter of this specication, and the general principles of surveying employed in the old and new instruments are the same, but the adaptation is entirely different.
The high oblique plotter and Mr. Millers instrument apply the same general surveying'principle, but in design they are more closely related to the largely mechanical plotting machines than to the simpler instruments used by surveyors in the iield.
In the present invention it is proposed to make the` practice of photogrammetric surveying similar to that of the plane table and alidade already so familiar `to topographic engineers, and t'o make the apparatus used therein as simple and 'fool-proof as possible.
The new instrument with which. this speciflcation is concerned has been described in published articles as follows: A New Photoalidade by R. M. Wilson, published on November 6, 1937 in The.Military Engineer, vol. ICEX, No. 168, Nov.-Dec. 1937; Oblique Photographs and the Photoalidade by R. M. Wilson published in Photogrammetric Engineering, issue of April-May-June 1938. The instrument was exhibited at the annualmeetings of the American Society of Photogrammetry and the Geological Society of America, held in Washington in 1938.
The photoalidade described in this speciflcation is not like the stereoscopic plottingmachines now in common use vin the art of photogrammetry-such as-the aerocartograph, the Istereoplanograph, the multiplex projector, and others, because these machines employ the principles of stereoscopic vision, and ordinarily are used with vertical axis photographs. Also, these machines are very complicated and are so expensive as to be beyond the reach of. ordinary surveyors; they are described in texts on photogrammetry and in articles published in technical journals. l
An object of the present invention is to provide a device enabling one to make maps from oblique photographs using the methods of intersection for position and trigonometric leveling for altitude that are ordinarily used with a plane p table` andtelescopic alidade in mapping from ground stations.
Another object of the invention is to provide an instrument by means of which the same observations may be made from a photograph that a surveyor might make if he could set up his plane table at the point where the picture was taken.
Another object of the invention is to extend graphic control with oblique photographs as an aid in strengthening the compilation of vertical photographs into mosaics or planimetrie maps.. A still further object of the invention is to provide a means lfor making slotted templates information on photographs taken as records into .f
the form of true scale plans or diagrams. For example, photographs of a street traffic accident,
taken from two or more dierent points of viewprepare a. plan of the locality with vehicles and other objects shown accurately to scale in their relative positions.
Other objects and advantages. of the invention will be apparent to one skilledin the art to which the specification relates in the light oi the accompanying drawings in whch- Fig. 1 is a perspective view of the new photoalidade.
Fig. 2 shows in section the details of the optical collimator.
Fig. 3 is a above, while Fig. 4 is a side elevation.
The instrument includes a supporting frame, carrying a holder for a photograph, a sighting telescope mounted so as to move as a unitwith a vertical spindle, and a ruler-attached to the spindle which guides the drawing of lines of direction on a map corresponding to directions sighted to features on the photograph, together with means whereby vertical angles may be observed for calculating difference in altitude, and an optical collimator for placing a given point on the map exactly in the vertical axis of the spindle, extended.
may be used to plan view of the instrument from In the drawings reference numeral I denotes t a triangular frame having three widely spaced legs 2 which hold the frame above a Work table at a height convenient to the operator, leaving the table top nearly free for laying out the maps or drawings being worked upon. Supported by the triangular frame I is a sighting telescope l, mounted comparable to the telescope in a surveyors transit, so as to point up or down, tilting upon the horizontal supporting axis 4 at right angles to its line oi' collimation shown bythe line 5. 'Ihe tilting motion of the telescope 3 is controlled by a clamp 8 and a slow motion screw 1 similar to the mechanism of the conventional surveyors transit. A vertical angle arc and Vernier scale 8 is provided so that angles of elevation or depression of the telescope can be measured. The vernier is adjusted to read zero when the line of collimation of the telescope is at right angles to the vertical axis 9 of the instrument. The line of collimatlon 5 and the two axes 4 and 9 pass through a common point l0 to be referred to hereafter as the center of the instrument.
The telescope mounting II is carried on the upper end of a spindle I 2 which turns in a bearing i3 fastened to the main frame of the instrument. The telescope mounting can be revolved with respect to the spindle, this motion being controlled by a clamp I4 and slow motion screw I5. Thus .the telescope may be pointed in diiferent directions by turning it about the vertical axis 9 in order to-pointto ,any part of the photograph I6 from which measurements are to be taken.
The photograph is clipped to the holding plate This plateis so mounted on parallel bars I8 that it can bemoved toward or away from the center I0, but the plane of itssurface is held desired distance from the center i0. The bars are pivoted on pivots I9 and 20 and form part of the framework upon which the photograph I6 is carried. Therefore the entire framework may be elevated or depressed by rotation about the axis 2| which, by construction, passes through the center I0 and is at right angles to the vertical axis 9. The position of tilt of the bars I B may be maintained by the clamp 22 and slow motion screw 23. Thus a point 24 may be marked on the plate I1 from which a line erectedperpendicular to the plate will also pass through the center I0. 'I'he photograph IB is fastened to the plate I1 with its optical center superimposed exactly on the marked point 24 on plate I1 so that the optical or principal axis of the photograph. thus constrained to coincide with the perpendicular just mentioned, will also pass through the center I 0.
Also, the photograph may be revolved about its center on the plate to further adjust it in prop-er position. By the adjustments described the photograph can be placed relative to the center I0 so that as seen from that point as perspective center it will represent accurately the actual view as seen from the camera station.
To the lower end of the spindle I2 is hingedly fastened the arm 25 which is attached to the spindle by the hinge 21. The ruler 26 used to draw lines upon the` map or work sheet is hingedly fastened to the end of the arm 25 opposite the spindle I2 by means of the hinge 28. The axes bf the hinges 21 and 28 are parallel. By this arrangement the ruler 26 lies flat and adjusts itself to the minor irregularities of the map surface, and it may be lifted easily to be out of the way when inspecting or moving the map, but still it is controlled so that its ruling edge always passes through the point where the vertical axis l intersects the map, indicating directions from that point correspondingto the directions in which the telescope is used.
'Thus it is seen that with the clamp I4 tightened the telescope 3, spindle l2, arm 25, and ruler 2,8, all must revolve together through the same angles about the same vertical axis 9.
As it is necessary to place the map under the instrument with a given point on the map exactly under the center I0, an optical collimator is built into the'spindle I 2, the line of sight from its eye piece 20 being turned downward by the prism 30 through the objective lens 3i, so as to show where the vertical axis 8 intersects the plane of the map. 'I'he map can be shifted until the given point appears at the intersection of the cross hairs in the collimator.
The function of the photoalidade is to utilize, for surveying purposes, the information-contained in oblique photographs taken from airplanes or from ground stations. When the position, altitude, and orientation 4of the camera are ,determined for the instant o1' an exposure, the resulting photograph can be used in the photoalidade: First, to draw lines of direction upon through the locations of points identified on the photograph and, second, to read vertical angles at all times -at right angles to the direction of as recorded by the photograph at the camera station from the horizon to points on the ground.
If the camera is not used at an established ground station where it can be carefully leveled, and where its position, elevation, and orientation can be determined directly, it is necessary to resort to the these elements for the, camera station. The reprinciples oi' resection tc determine vations may be determined also.
have been taken froman airplane. If three or -more properly distributed control points, whose positions and elevations are known, can be identitled in the photograph, the resection is usually possible.
In general, the angles formed between lines to these control points from one point of view are not duplicated from any other pointof view. It follows, therefore, that the angles may be used to determine the position of the point Iof view with respect to the control points. In plane surveyingthis is called the Three point problem; the solution is more complicated when three dimensions are involved, although the principle is the same. There aref'istablished methods by which the position and altitude of the camera station can be determined by mathematical computations, beginning with measurements made on thephotogaph between the images of the control points. Such rigorous solutions are very laborious. But the photoalidade can be usedto solve the problemgraphically in av yery" short time', using .the method describedin the published article entitled Oblique Photographs', and the Photoalidade (April, May, June 1938, Photogrammetric Engineering, pp. 65-74) which is incorporated herein by reference. The method is one of successive approximations, but leads quickly to a solution that is'within the limits of error of the work done by the instrument.
. graph should then represent the leveled, its optical axis was When the position and orientation of the camhave been determined by resection and the corresponding era station from the control points,
settings of the instrument are efiected)angular^35 measurements taken with the telescope will be the same as if the surveyors ,instrument were set up at the camera station, taking angular measurements from that point to the actual landscape. Thus, lines of direction may be observed to new points whose locations are sought. Such lines radiating from only one camera station, resulting fi'omthe use of a single photograph, do not immediately locate the new points; it is necessary to obtain similar radiating lines to the same points from another camera station. Then the positions ofthe points sought are found where, corresponding lines from the two camera stations intersect. This is the well known principle of intersection that has been used in plane-table surveying for a great manyy years. The use of the photoalidade makes it possible to use this principle of intersection from camera stations in the air just as it has been used in the past from plane-table stations on the ground.
Vertical angles also may be measured to the new points whose positions have thus been determined, and by a simple calculation their le- These points then may be used to guide the sketching of contours in reconnaissance mapping, or to use as control for compiling vertical photographs by other methods of photogrammetry.
The method may be used also with photographs taken with ordinary hand cameras, recording progress in engineering construction, to locate points of particular interest. Photographs taken immediately following a. traiiic accident may be used in the photoalidade to determine the position of vehicles. obstacles, or other objects that may be important .in the case.
To describe the manipulation of the instrument, consider rst the most simple case when a photograph has been taken from a ground station of known elevation, with the camera accu- Then the inclination of rately leveled. The horizontal axissof the phototrue horizon. Now, referring to Fig. 1, slide the holder I1 forward or back on frame, until its front face is at a distance from the center of the instrument l0 that is equal to the focal length of the camera. Prick a smalll hole in the photograph where the axis passes through its center. The photograph I6 is placed on the holder Il with'its pricked center on the center point of the holder. Since the camera was horizontal, therefore set the reading of the Vernier 8 so that the line of c'ollimation 5 willbe perpendicular to the main axis 9 of the instrument. Then (see Fig. 4) by the clamp 22 and slow motion screw 23 raise the holder I1 and its frame I8 until the leveled line of collimation 5 will pass through the center of the photograph when the telescope is pointed in its direction. Next rotate its center on the'holder until its horizontal axis is in the plane at right angles to the axis 9 of the instrument so that looking through the telescope 3, the intersection of its cross wires (which represent the line of collimation) appearA to follow along the horizontal axis of the photograph as the telescope is turned from side to side.
Butgenerally the camera will not be leveled exactly; in fact it is usually desirable to tilt the axis of the camera down/to include more of the landscape and waste less of the photograph on sky. Also, the camera may not be leveled transversely. Thus the line on represents the true horizon generally does not coincide with the horizontal axis of the photograph, but instead it is most often near and only approximately parallel to the upper edge of the photograph. If the camera was used at a ground station of known position and elevation, and control points appear inthe photograph, it is easy to Vcompute the true vertical angles from the camera to those points.
The photograph I6 is placed as before on the holder l1 with the distance from l0 to 24 equal to the focal length of the camera.` -the holder ,arms I8 are adjusted by the clamp 22 andY slow motion screw 23, and the photograph is rotated on yits ce er, until the computed vertical angles read correctly on the arc and Vernier 8 when the telescope is pointed to the corresponding imageof the respective control points. The` trueV orizon line may then be drawn by noting the line that the orosswires follow across the photograph when the Vernier 8 is set at zero, and the telescope is swung from side to side.
If thecamera is not and elevation of the camerastation is not known, which is usually the case when photographs are takenvfrom an airplane, it is necessary to draw a tentative horizon line n the photograph by rough estimation. Setting the photograph inthe instrument .so that this tentative horizondine lies in the plane perpendicular to axis 9 at point I0. Then by test observations it is possible to determine how much the inclination of the holder I1 should be changed by adjusting the slow motion screw 23, and how much the photograph should be turned about its center to refer further measurements to the true horizon.
When the photograph has been adjusted into place byone of the methods just outlined, the operator is ready to take observations upon any features or details in which he may be interested that show in the photograph.v The map or plan upon which he is working is laid on the the graduated bars I8 of thethe photograph about the photograph that leveled, and the position f der the instrument passing through the until the pointon it representing the position of the camera station is `directly in the line of the 1 vertical axis 9 of the instrument. This is accomplished by sighting through the.` centering collimator shown in Fig. 2 with prismatic eyepiece 29, right angle prism 3G and objective lens 3l so arranged that its line of collimation is turned downward to coincide with the axis il. With the clamp i-i loosened the operator lays the ruler 26 along a line on the map that corresponds to the direction of a sight to a control point on thefphotograph, and directs the telescope to that point. Clamp it is then tightened to preserve the directional relationship between the line of coilimation 5 of the telescope and the ruling edge 26. Then with his left hand the operator holds q the far end of the ruler 2t at 2li and swings it, and the telescope 3 that now turns with it, to view any desired part of the photograph. With his right hand the telescope may be tilted up or down as may be necessary, and when the pointing is effected, a corresponding line of direction may be drawn upon the map along the edge of ruler 2t. The vertical angle to the sighted point is read from the arc and Vernier 3 at the side of the telescope.
The legs Z hold the instrument on its frame i at a convenient height above the table. The operator can, at any time, lift the ruler 26 from the map without disturbing -the settings of the instrument, because the hinges 2l and 28 are so arranged as to control the direction of the ruler 2t, yet allowing it to be lifted up out of the way. Thus the placing of maps or drawings unis a simple matter.
What is claimed is:
1. An instrument for use in the making of maps from oblique photographs, comprising a supporting frame adapted to be placed ona drawing table to over-lie and allow relatively free access to a mapping surface on said table, a spindle mounted on said supporting frame for rotation about an axis substantially normal to the plane of the mapping surface thus established, a sighting device for establishing. a line of sight, said sighting device being pivotally mountedon said spindle with the line of sight thereof intersecting the axis of said spindle and with the pivotal axis point of intersection of the line of sight and the axis of said spindle normal to the plane established thereby, an arm having one end hingedly attached to said spindle, a ruler hingedly attached to the other end of said arm with the hinge axes at opposite ends of said arm parallel tceach other-and to the plane of said mapping surface, whereby the ruler may lie fiat on said mapping surface yet permitting it to be raised therefrom, said ruler being so positioned that the line defined by one edge thereof intersects the axis of rotation of said spindle, a 'support carried by said frame for supporting a photograph in viewable relation -to said sighting device, means for adjusting the distance of the photograph support from said sighting device and means for adjusting the angle of tilt of said photograph support.
2. An instrument for use 1n' the making of maps from oblique photographs, comprising a `supporting frame adapted to be placed on a vdrawing table to over-lie and allow relatively free access to a mapping surface on said table, a spindle mounted on said supporting frame for g rotation about an axis substantially normal toagencer the plane of the mapping surface thus established, a sighting device for establishing a line of sight, said sighting device being pivotaliy mounted on said spindle with the line of sight thereof intersecting the axis of said spindle-and with the pivotal axis passing through the point of intersection of the line of sight and the axis of said spindle normal to the plane established thereby, an arm having one end hingedly attached to said spindle, a ruler hingedly attached to the other end of said arm with the hinge axes at opposite ends of said arm parallel to each other and to the plane of said mapping surface, whereby the ruler may lie flat on said mapping surface yet permitting it to be raised therefrom. said ruler being so positioned that the line delined by one edge thereof intersects the axis of rotation of said spindle, a platen for supporting a photograph carried by said frame on a member pivoted on an axis perpendicular to the axis of said spindle and intersecting the same and said line of sight, and means for adjusting said platen longitudinally of said member whereby the distance from the sighting device and the angle of tilt of the platen may be adjusted with respect thereto.
3. An instrument for use in the making of maps from photographs, comprising a supporting frame adapted to Abe placed on a mapping surface to over-lie the same and allow relatively free access thereto, a spindle mounted on said supporting frame for rotation about an axis substantially normal to the plane of the mapping surface, a sighting telescope for establishing a line of sight, said telescope being pivotally mounted on said spindle with the line of sight thereof intersecting the axis of said spindle and with the pivotal axis passing through the point of intersection of the line of sight and the axis of said spindle normal to the plane established thereby, an arm having one end hingedly attached to said spindle, a ruler hingedly attached tothe other end of said arm with the hinge axes at opposite ends of said arm parallel to each other, and to the plane of said mapping surface, whereby the ruler may lie fiat on said mapping surface yet permitting it to be raised therefrom, said ruler being so positioned that the line defined by one edge thereof intersects the axis of rotation of said spindle, a picture supporting platen mounted on said frame, said platen being adjustably mountedl with respect to said sighting telescope.
4. An instrument in accordance with claim 3 in which the telescope includes means for measuring vertical angles.l
5. An instrument. for use in the making of maps from oblique photographs, comprising a supporting frame adapted to be placed on a mapping surface to over-lie the same and allow relatively free access thereto, a short focus telescope mounted on said frame for universal movement in azimuth and elevation, a ruler adapted to lie in the plane of said mapping surface, said ruler being hingedly attached to the mounting of said telescope to be traversed therewith in azimuth by means of an intermediate linkage pivoted both to the'telescope mounting and to said ruler about axes parallel to each other and parallel to said mapping surface, and a photograph rsupporting platen mounted on said frame for supporting a photograph in adjustable viewable relation to `said telescope in a plane oblique to the plane of said mapping surface whereby the telescope may be pointed successively at points on a photograph carried by said platen with the ruler moving azimuthally therewith on the mapping surface to indicate lines on said surface enclosing angles corresponding to the angular movement between sightings of the telescope.I
6. An instrument in accordance with claim including means for adjustably positioning the said telescope azimuthally with respect to said ruler.
7. The method of making maps on a mapping surface from a plurality of photographs of the same general locale made from different points, which comprises setting up rst one of said photographs with respect to a reference point so that the angles subtended by said photograph at said reference point are similar to the angles subtended by the field photographed at the point said photograph was taken, and with the vertical angles of lines of observation from said reference point to various points on said photograph corresponding to the vertical angles of the lilies of observation from the point said photograph was taken to the respective points on the field photo, graphed, locating a point on said mapping surface representing in plan the point said photograph was made, sighting from said reference point to objects on said photograph marking the azimuthal directions of said objects from said reference point upon said mappingv surface from the point thereon corresponding to the point said photograph was made, setting up a second one of said photographs with respect to a second reference point in the manner outlined in connection with the rst photograph, locating a point on said mapping surface corresponding in plan to the point said second photograph 'was taken, sighting from said second reference point to obto the angles subtended by said objects in the area itself at the point of origin ofthe photograph, locating on a mapping area a reference point corresponding in plan to the point of sight of the set-up, marking relative to said point of sight on said mapping area angles in azimuth corresponding to the azimuth angles relative to said point of sight of points in said photograph, repeating the set-up and azimuthal angle marking with respect to a second photograph and a reference point located relative to said first reference point on the mapping area to correspond with the relative location of the corresponding points of origin, whereby the relative positions of points common to the two photographs are located on a mapping area bv4 intersection of the azimuthal markings thereof.
9. The method of mapping which comprises taking with cameras of known focal lengths and at determinable vertical angles of principal axes from a plurality of points of origin, a plurality of photographs of an area to be mapped; setting up with respect to a point/of sight, one of said photographs, with its optical center at the known focal distance and the determined vertical angle of principal axis from the point of sight, and with its plane oriented s o that angles subtended at the point of sight between images on thephotograph, correspond to the angles subtended between corresponding points in the area itself at the' point of origin of the photograph; locating on a mapping area a reference point corresponding to the jects on said second photograph, marking the directions of said objects from said second reference point upon said mapping surface from the point -thereon corresponding to the point from which said second photograph was taken, and xing on said mapping surface the positionof the objects viewed in said photographs from the intersection of the lines marked on said mapping surface representing two lines of sight to the same objects.
8. The method of mapping which comprises taking a plurality of oblique photographs from a plurality of points of origin of an area to be mapped, setting up with respect to a. point of sight one of said photographs with the optical center at the same distance from said point as the lens -of the camera taking the picture was point of sight of the set-up, marking relative t0 said reference point on said mapping area angles in azimuth corresponding to the azimuthal angles relative to said point of sight of points on said photograph; repeating the set up and azimuthal angles making with respect to a second photograph and a reference point located relative to said first reference point on the mapping area to correspond with the relative location of the corresponding points of origin; whereby the relative positions of points common to the two photographs are located on the mapping area by intersection of the azimuthal markings thereof.
l0.A A photoalidade for use in the making of mapsv from a plurality of oblique photographs comprising a short focus telescope mounted for movement in azimuth and elevation, a ruler carried by said telescope when moved in a plane oblique to the horizontal plane in an azimuthal direction, said ruler being attached to the same vertical spindle that carries saidr telescope,vand adjustable means for holding a photograph in was made and with the vertical angle of the prinfrom the sensitized area on which the photograph the same position with respect to said telescope that the original field photographed occupied cipal axis from the point of sight to the optical center of the 'picture the same asrthe vertical angle of the principal axis of the camera was when the picture was taken, and with its plane oriented so that the angles subtended at the point of sight by objects on the photograph correspond with respect to the camera taking .it whereby when the telescope is moved in azimuth the ruler moves therewith permitting plane table surveying directly from a plurality of photographs.
RONALD M. WILSON.