Patent GB-182934-A (GB)
Title: Improvements relating to the production of landscape outline and other sketches
IPC: G01C17/12
Filed: 1921-04-13
Abstract: 182,934. McCallum, J. W. April 13, 1921. Drawing or sketching appliances.-In apparatus for facilitating landscape and other outline sketching, of the type in which the features seen from a definite point through a limited observation opening are depicted on a transparent sheet, the observation opening is made in an eyepiece mounted on a carrier which is rotatably fitted on a support with the axis of rotation passing through the plane of the opening, the transparent sheet being carried by a frame also rotatable about the same axis. The device as shown in Figs. 1 and 2, adapted for use in survev work, is mounted on a tripod carrying a theodolite head 2 provided with a turntable comprising a graduated circle 3 and a plate 4, on which is mounted a supporting-table 7, adjustable by nuts 8. Mounted on the table 7 is a standard 10 carrying a support 13 which is adapted to rotate on a pin 12 in line with the axis of the theodolite head 2, and, if desired to be locked in position. The support 13 is provided with an eyepiece 16 in which is formed a small observation opening 17. Adjustably mounted by means of a depending screw in a slot 9 in the table 7 is the lower member 22 of the sheet-supporting frame, which also comprises an upper member 29 and upper and lower portions 27, 25 of the side members, the parts being hinged together to facilitate packing. The upper portions 27 of the sides are held upright by clips 31 on extensions 30 of the lower portions 25. A transparent sheet 37, provided with vertical and horizontal lines intersecting near the centre of the sheet. is clipped on to the frame by upper and lower resilient members 41, 42 engaged bv straps 35 on the ends of the members 22, 29. The sheet may be held temporarily in position, to facilitate clamping, by means of loops 38 thereon engaging pins 36 on the members 22, 29. The outer edges of the members 22, 29 have a common radius from the observation opening 17, so that equal divisions on the sheet will represent equal degrees of arc. Cleats may be provided to enable the sheet to be clamped at various distances from the eyepiece. The lower portions 25 of the side members of the sheet-supporting frame are provided with a pivoted arm 45 carrying a bracket 46 on which rests one end of a carrier 47 for a spirit level 49, the other end of the carrier being supported in the observation opening 17. When the device is levelled, the upper ends of the brackets 46 indicate the position to be occupied by the horizontal line on the sheet. When ready for use, the device must be oriented for use in the usual way each time a new sheet is inserted, as the vertical line may not occupy the same position each time. In the device shown in Fig. 6, which is especially adapted for perspective drawing, the sheet-supporting frame is adjustable on the table 7 which slides in guides 52 on the lower member of the frame and is clamped in position by a bar 53. The frame comprises the lower member 51 and side members 56 hinged thereto, the outer edge of the member 51 being straight, so that, if the device is used for surveying, correction would have to be made for the variations produced in the length of degrees of arc. The members 56 may be disposed backwardly from the edge of the member 51 to provide a rest for the lower edge of the transparent sheet which is retained by lips 159, the upper edge being held in position against supports by pivoted cleats 62. The side members 56 are provided with brackets 57 which support pivoted links 66 to each of which are pivoted, through the medium of an arm 69, supports 72 for the outer end of the level-carrier 47. In case the distance of the sheet from the eyepiece 16 is less than the length of the carrier 47, the arms 69, which are retained in position by wing nuts, may be removed and attached to the links 66 outside the sides 56. In the modification shown in Fig. 10, two mirrors 75, 76 disposed at an angle of forty-five degrees to the direction of the field of view and to the vertical respectively are carried in a casing 77 which may be mounted on a theodolite head and tripod. The view, seen through an observation opening 82 in an eyepiece 80 which is adjustably mounted on a standard 79 attached to the casing, is drawn on a transparent sheet 83 disposed between the eyepiece and the mirror 76. The mirror 75 may be dispensed with, in which case the sketch made would be in reverse.