A VISUAL FIXPOINT MARKER SYSTEM

Abstract: A visual fixpoint marking of the light type (4, 12) is completed by an underlying marker (2) of the "subterranean" type, the electric or magnetic axis (a) of which intersects the ground or road surface in the visually marked fixpoint (C). The visual marker element (4, 12) may disappear or get displaced, but the fixpoint marking will then be easy to reestablish, viz. by locating the axis (a) of the subterranean marker by means of a search detector and remounting the visual marker element (4, 12) in accordance with the refound location of the fixpoint (P.C). The lower marker (2) is arranged so as to remain non-influenced of the upper marker element being removed or laterally displaced.

Description: A visual fixpoint marker system, The present invention relates to the design and the provision of a visually marked fixpoint on the ground or in a road surface., particularly for cadastral use. It is well known that light marker elements such as boundary po.sts and road nai ls may easily disappear by removal or covering, just as boundary posts and corresponding light arker e_l ments may be ti lted or displaced in an incidental or even intensional manner, whereby the marking either disappears completely or becomes incorrect or at least unreliable. More important fix- points, therefore, are not marked by means of light marker elements, but to the contrary by large and heavy elements such as a concrete block in the ground on which the fixpoint is marked. It is already known, however, that such heavy and for that sake even the light marker elements can be entirely avoided, since they can be replaced by subterranean electromagnetic markers, which are locatable from above by means of a suitable search detector equipment, whereby the fixpoint is determined as. the point of intersection between the ground or road surface and a vertical electromagnetic axis of the subterranean marker. Reference is here made to WO 83/01306, in which a relevant type of such a marker is disc losed. For the geodetic practice it may be sufficient with such invisible, yet detectable fixpoints, but in the Land registration practice or cadastral practice it is maintained that cadastral fixpoints should be visually marked, even though in practice only or mostly the said light marker elements are used, despite their acknowledged instabi lity. It is consequently accepted that a considerable surveying work may be required for reestablishing a disappeared or displaced fixpoint. It is the purpose of the invention to provide a visual fixpoint marking which may be of the said light type, without a reestablishing of the fixpoint being particularly difficult upon a possible removal, covering or displacement of the visual marker element. According to- the invention this is achieved by providing underneath the visual marker, as being of the said Light type placed in the ground or road surface, a marker of the said subterranean type, the electromagnetic axis of which coincides with the visually marked fix¬ point, without any rigid mechanical connection existing between the subterranean marker and the visual marker element. If the Latter element happens to disappear or to be displaced it will thus always be possible to ascertain the correct position of the fixpoint by using the said search equipment, whereafter the visual marking thereof may be renewed or adjusted correctly. What is here important is that the displacement or the covering of the marker element in the ground or road surface will not affect the marker effect or direction of the underlying subterranean marker. In connection with the invention, therefore, it will still be the visual marker which provides for the official and immediately usable marking of the fixpoint, while the subterranean marker is just a security element which will fac litate a reestablishment of the visual point marking without any need of an associated surve ing work. In the following the invent on is described in more detail with reference to the drawing, in which: Fig. 1-3 are side views of various marker systems according to the invention. Fig. 4 is a perspective view illustrating the mounting of a visual marker on a road surface, Fig. 5 is a side view of a marker placed in such a surface, and Fig. 6 is a lateral sectional view of a modified embodiment of the invention. In the embodiment shown in Fig. 1, 2 designates a subterranean marker, which may be mounted at a depth of e.g. 1-1 1/2 m, and the electromagnetic axis a_ of which projects vertically upwardly so as to intersect the ground surface, designated ϊ_, in a point P. Above the marker 2 there is placed, in the ground, a pipe element 4 consisting of plastic or another durable materiaL and being provided with outer, triangular radial fins 6, which project from a bottom plate 8 upwardly along the pipe 4 and inwardly towards the pipe so as to end somewhat below the upper end of the pipe 4. The pipe 4 is provided with a top plate 10 as shown extracted from the pipe, this plate being provided with the seal of the relevant authority and with a center mark C, which, by the mounting of the tube 4, is brought to register with the marker axis a_. The tube 4 is mounted in the ground such that the top plate 10 is located in or slightly above the ground surface b. By virtue of the ou-twardly projecting bottom plate 8 the tube 4 wi ll be stabilized against vertical displacement, and the radial fins ό will stabilize the tube against displace¬ ment and ilting in the horizontal direction. Local side displacements of the uppermost earth layer around the tube will be resisted by the tube 4 due to the radial fins ό being absent in this upper area. In the carefully ready mounted position of the tube element 4 the point marking C will be located in . or just above the point P, and the point C will be the official fixpoint. The top plate 10 ill be horizontal, and a defect is easily observable i.f the top plate 10 is found to be non-horizontal, as the tube 4 must then have been tilted. In such a case as well as when the visual ' fixpoint marking has disappeared entirely or partially from a given local area, whether due to a removal of the pipe element 4 or a covering of the upper end thereof, the correct visual fixpoint marking may be reestablished by moving the_said search detector equipment over the relevant Local area until the point P is Located thereby. Thereafter the tube 4 may be Lined up or remounted for a correct mutual positioning of the points C and P, whereafter the point C is again defining the official fixpoint. An already existing fixpoint defined by a "light" marker may well be provided with a subterranean marker, viz. by marking the fixpoint at the ground surface on an e.g. upwardly tiltable plate member or wire cross frame then providing the required mounting hole for the marker 2 and mounting the marker therein; before the filling of the mounting hole it should be checked by means of the search detector that the marker axis _a intersects the point as marked on or by the now reposi t ioned, tiltable plate member or wire cross frame. Thereafter the tube element 4 is mounted in a hole of the required Larger width, for accomodating the bottom plate 8, and the tube element is adusted until the point C is located coinciding with the point marked on or by the said plate member or wire cross frame, whereafter the tube element 4 is stabilized by filling up ts mounting hole. A fixpoint on a hard surface such as a road surface may be marked by means of a road nail 12 as shown in F g. 2, inasfar as at such places the risk of a lateral displacement of such an element will normally be very low. On the other hand such an element may very well be covered by a new road coating so as to disappear thereby. However, when the fixpoint has in such a case been coarsely marked, e.g. by a temporary marking at the road side, it wi ll thereafter, upon the Laying out of the new road coating, be easy to Locate the fixpoint by means of the search detector and to thereafter provide for a new and accurate marking of the point, e.g. by means of a new road nail, which, if required, may be mounted in a verticaL bore in the underlying original road nail 12, which may consist of metal or plastic and have the pronounced conical shape as shown in Fig. . Even though it is very important that the subterranean marker is in no mechanically r gid connection with the visible marker, it is nevertheless, according to the invention, possible to make the two markers appear as or in a preasse bled and adjusted unit, which is mountable in the ground such that the visual marker is already correctly located relative the axis of the subterranean marker. Such a unit is shown in Fig. 3, in which the subterranean marker 2 is mounted in the lower end portion of a tube 14, which is topwise closed by a stopper having an upper, enlarged head portion 16, on which the point C is marked. It has been controlled by the manufacturer of the unit that the center point C on the head portion 16 is located in the electromagnetic axis of the marker 2. The tube unit 14 is mounted in a suitable, verticaL hole in the ground such that the stopper head 16 is located at the ground surface. Hereafter it will be a non-desired situation that a side pressure on the upper end of the tube 14 will cause the tube as a whole to tilt in the ground, but this situation is counteracted in that the tube 14 is provided with one or more annular weakened areas 18 as shown in dotted Lines, such that the tube 14 in the said situation will break in this or these areas, while the lower part of the tube 14 will be stabilized against . ti Iting by the retaining action of the surrounding ground. The weakened area or areas 18 may be provided as easily breakable areas of an otherwise monolitic tube 14, but they may also be provided as planes of separation between adjacent, non-integral tube portions, which may be temporarily interconnected e.g. by a wrapping of an adhesive tape, which wilL hold the tube portions together in a reasonably stiff manner until the tube has been mounted in the ground, while the connection by the adhesive tape will not thereafter be sufficient to prevent a breakage of the tube way down in the ground if the upper end of the tube is exposed to a Lateral displacement. The influence of the humidity of the earth will contribute to make the adhesion Less effective after the mounting of the tube . As shown at the Lower end of the tube 14, immediately above the lower marker 2, an alternative arrangement will be that two adjacent tube portions are interconnected by means of axially projecting pins 20, which are provided axially displaceably in the wall materiaL of the tube, so as to allow the overlying tube piece to be broken outwardly from the underlying tube piece such that the latter tube piece as holding the marker 2 will not change its position should the uppermost tube piece be tilted. The structure as shown in Fig. 3 may even be modified to the use of separate tube portions which are product onally piled and then subjected to a cast ng out or foaming up of a foam materiaL which will stabilize the tube during transportation and mounting thereof, but will break whenever the opposed two tube portions are exposed to a considerable mutual break action. For the visual marking of a fixpoint on a road su ace it is possible, as mentioned, to make use of a road nail, but Fig. 4 illustrates another and preferred method of establishing such a marking. Upon the mounting of the subterranean marker 2 and possibly upon an earlier surface marker having been covered by a new bitumenous road surface layer the fixpoint is located by means of the search detector, and in the fixpoint P as found hereby is placed a vertical rod or stiff wire 22. A circular area 24 of the road surface around this rod is heated by means of a burner 26, and a thermoplastic disc 28 having a central hole 30 for receiving the rod 22 is lowered over the rod 22. Also this disc 28 is heated to softening, whereafter it is pressed against the road surface by means of a die rod 32, which is likewise centered by means of the rod 22; the die rod will die-stamp in the heated and softened upper surface of the disc 28 the official seal of the relevant authority, while the correspondingly softened lower surface of the disc 28 is pressed against the softened road surface in the area 24 for in imate connection therewith. If necessary, the upper layer of the softened road surface can be scraped off such that the disc 28 may be mounted flush with the road surface. After the mounting of the disc the rod 22 is retracted, whereafter the disc 28 through its center hole 30 will mark the fixpoint visually. It may be difficult to select a thermoplastic material for the disc 28 which will favour both a good- coherence to the road surface at a temperature suitable for this purpose and the desired die-stamping of the disc surface at practically the same temperature. Advantageously, therefore, as shown in Fig. 5, a disc 28 may be used which is a sandwich of a lower disc portion 34, which is suited for connection with the road surface at a relatively low temperature, e.g. 70-80 C, and an upper disc portion 36, which is pre- welded to the Lower disc portion and has a higher softening temperature, whereby the upper disc portion 36 may already in advance be provided with the desired marking, while for the pressing of the disc 28 onto the road surface a pressing tool 32 may be used which is not addi ionally a die-rod. It is important that the disc element 28 is mounted slightly countersunk in or flush with the road surface, such that it does not project therefrom, whereby it could be scraped off by some strong interaction e.g. with a snow plough. In Fig. 6 is illustrated a further mounting method, whereby a hole 40 is made in the ground and a mounting rod 42 having the same diameter as the marker 2 is Lowered into the hole. Thereafter a plurality of separate tube pieces 44,46 and 48 are Lowered over the mounting rod 40, whereby the tube pieces will be mutually centered by the rod 40. The hole 40 is filled up outside the tube pieces, while it is checked that the rod 40 remains vertical, and thereafter the rod 40 is pulled up. A marker 2 is then Lowered into the tube 44,46,48 to be deposited in the Lower tube piece 44, and prefer¬ ably the remaining tube is filled by a solid foam material, optionally by lowering into the tube a prefabricated rod or Lining tube of a suitably breakable materiaL. The tube can be closed topwise by a cap. If desired, the upper pipe piece 48 may be provided with a horizontal flange plate 50 for counteracting a Lifting of this tube piece, and even radial wings 52 may be provided for stabilizing the tube piece against lateral displacement. The upper end of the tube may be located in or slightly above the road or ground surface.* It should be checked in advance that the electromagnetic axis of the subterranean marker 2 is exactly axially parallel with the marker. It is a condition, of course, that the employed subterranean markers are locatable with an accuracy of the same magnitude as required for the visual marking.

Claims: C L A I M S : 1. A fixpoint marking of the visual type, comprising a Light marker element mounted in a ground or road surface, and on which the fi point is marked, characterized in that underneath the marker element there is mounted a marker of such a "subterranean" type, which is locatable from above with good accuracy by means of a suitable search equipment, this marker having a detectable e Iect ri c/magneti c axis and being mounted such that this axis projects through the marked fixpoint on the visual marker element, the marker element and the subterranean marker being arranged in such a mechanically mutually independent manner that the visual marker element may be Laterally displaced or tilted ithout such movement being transferred to the subterranean marker. 2. A fixpoint marking according to claim 1, characterized in that the subterranean marker is mounted in a tube, which carries the visual marker element at its top, and w ich s made in an easily breakable manner. 3.. A fixpoint marking according to claim 1, characterized in that the visual marker element consists of a disc, which is fuse bonded to a road surface above an already mounted subterranean marker. 4. A method of establishing a fixpoint marking according to claim 1, whereby a marker element of a light type, on which the fixpoint is marked, is mounted in a ground or road surface, characterized in that prior to the mounting of the marker element there is mounted, underneath the mounting area of the marker element, a marker of the "subterranean" type, and that the marker element is finally mounted with such a location that the from above detectable axis of the subterranean marker intersects the fixpoint marking on the marker element, care being taken that any existing mechanical connection between the marker element and the subterranean marker is unstable against considerable lateral forces. 5. A method according to claim 4, characterized in that the subterranean marker is mounted in the ground housed inside a vertical tube carrying the visual marker element at its top end and being made in an easily breakable manner at one or more places thereof. 6. A method according to cLaim 4, characterized in Locating for the reestablishing of a visual fixpoint marking, the point of the road or ground surface which represents the axis of the subterranean marker and thereafter mounting or remounting the visual marker element with the fixpoint marking thereof coinciding with the axis of the subterranean marker. 7. A method according to claim 6, characterized by Locating, for reestablis ng of a fixpoint marking on a road surface, the axis of the subterranean marker and marking the same by sticking a rod or wire into the road surface, then lowering over said rod or wire a disc having a central hole for receiving the rod or wij*e and securing the disc to the road surface, preferably by fuse bonding, whereafter the rod or wire is pulled up and removed. 8. A method according to claim 7, characterized by the use of a sandwich disc, the lower surface of which is suited to be fuse bonded to the road surface by local heating, while its top side is advance prepared with a pressure resistant die-stamped authority seal.

Inventors: PEDERSEN WILLY PALLE, PEDERSEN, WILLY, PALLE
Applicants: PEDERSEN WILLY PALLE, PEDERSEN, WILLY, PALLE
Application year: 1985
Main classification: G01C15
IPC codes: G01C15