GB2253485A - Road surveying - Google Patents

Abstract

Road surveying method comprising taking vertical angle measurements of points on the roadway spaced apart along a notional line extending transversely across the roadway. For illustration a single point (15) for measurement is shown. The measurements are taken by an angle measuring instrument (19) comprising a pair of vertically-spaced theodolites (20, 21). All measurements are taken with respect to a datum defined by a marker (11) positioned on the road surface. For a complete survey, a series of markers (11) are positioned at spaced-apart intervals along the roadway. The method has the advantage that personnel do not need to step onto the carriageway in order to carry out the survey, and the road does not therefore need to be closed or restricted. <IMAGE>

Description

"ROAD SURVEYING METHOD AND SYSTEM" This invention relates to a road surveying method and system and in particular to a method and system for taking measurements of the level of the roadway.

When building new roads and repairing old, it is necessary to take measurements of the level of the road surface. On existing roads the degree of wear or subsidence can be detected and the measurements are used both in the operation of resurfacing, and in assessing quantities needed for repair.

A particular problem exists on roads that are in use because the existing methods rely on personnel standing on the carriageway at the position to be measured by means of electronic distance measuring equipment (EDM), and require that the section of road being measured has to be closed to ensure the safety of personnel. Thus, one or more lanes of a multilane highway may be coned off, leading to increased traffic congestion and risk of accidents, to say nothing of the cost of coning off the road in the first place.

British patent specification 2219399 describes a method of surveying which avoids this problem by using a reflector-less laser-type surveying instrument which is mounted on a vehicle and can be moved from one observation station to another by moving the vehicle along the hard shoulder or verge. However, reflector-less laser surveying instruments are expensive, and have a limited accuracy and other limitations. The present invention seeks to provide a method and apparatus which is capable of carrying out level surveys without the requirements to close a part or the whole of the roadway, and which is more adaptable and accurate than that described in GB 2219399.

According to a first aspect of the invention there is provided a method of road surveying comprising installing a series of spaced-apart height reference markers along the route of a road to be surveyed, placing an angle measuring instrument over each marker in turn and taking, at each reference marker, a series of vertical angular measurements of selected spaced points lying along a notional line extending from the reference marker and transversely across the road therefrom, said measurements comprising: 1) a first series of measurements at a first height above the reference marker; and 2) a second series of measurements at a second height above the reference marker, said second height being different from the first.

Each height reference marker defines a height datum relative to the immediately surrounding road surface over which the angle measuring instrument can be placed to obtain the aforesaid vertical angle measurements.

In accordance with a second aspect of the invention, there is provided a system for road surveying, said system comprising: a plurality of height reference markers each having means whereby they may be positioned along the route of a road surface to be surveyed and means to define a height datum with respect to the surrounding road surface; and an angle measuring instrument comprising first and second vertical angle measuring means, and support means for supporting said first and second vertical angle measuring means at respective first and second heights above the height datum defined by a said reference marker.

Said first and second vertical angle measuring means may be separate instruments, for example theodolites, positioned at different heights above the datum. However, in an alternative embodiment, the first and second vertical angle measuring means may comprise a single instrument, for example a theodolite, together with means for moving the instrument from said first height to said second height, and vice versa. In either case, once the vertical angle measurements have been taken at each height, simple geometry can be used to obtain the levels at the selected points with reference to the height datum defined by the respective reference marker.

The selected spaced points to be observed across the road are generally taken as alreadyexisting observable road markings, such as the white lines used to separate lanes or construction seams or other observable features. In this case, the points to be observed will be the points at which the above-referred to notional transverse line crosses the white line markings or other features.

The reference markers may take a number of forms, from simple marks on the road edge to relatively sophisticated constructions alongside the roadway.

In practice, however, the markers may generally comprise a simple metal rod having an enlarged head, similar to a nail, which is driven into the road surface so as to lie flush with the surface or slightly proud thereof. The top surface of the head defines the above referred to datum height. The markers are driven in at intervals to suit the survey specification corresponding to the required frequency of measurement.

In some circumstances, it will not be possible to position the markers on the metallised part of the carriageway, in which case they may be positioned in the ground surface off the edge of the carriageway.

The exact form of the markers in this case will depend upon the nature of this ground surface, but typically wooden or similar pegs driven into the ground could be used to support respective markers comprising metal rods having an enlarged head, of the type described above for direct application into the road surface.

Typically surveys are taken at 10 or 20 metre intervals along the road, and this thus dictates the marker spacing. The markers may be equally spaced, or may be spaced unequally, according to the particular circumstances, and the survey specification.

The markers are co-ordinated and levelled and the distance between them, whether equal or otherwise, is therefore known. Advantageously, and where possible, the markers are placed at the edge of the roadway, preferably a little back from the edge. For example, on a motorway, the markers can be positioned along the outer edge of the hard shoulder, thus keeping personnel well clear of fast-moving traffic.

Alternatively a wooden peg can be driven in completely clear of the metalled carriageway.

For complete knowledge of the position of the points being observed, it is necessary to know the bearing at which said notional line extends with respect to the road. For this purpose, measurements may be taken, at each height marker, of the horizontal angle observed to adjacent height markers on either side of the current marker. Preferably, for convenience, the notional line along which measurements are taken at each marker is the line which approximately bisects the horizontal angle between the bearings to these adjacent markers. Thus, on a straight road, the notional line will extend at right angles across the road. However, other angles are possible, and may be preferable in certain circumstances.

In order that the invention may be better understood, an embodiment thereof will now be described by way of example only, and with reference to the accompanying drawings in which: Figures 1 and 2 are respectively diagrammatic plan and edge views of a carriageway forming one half of a section of motorway; Figure 3 is a plan view of the motorway section illustrating the positioning of height markers; Figure 4 is a diagrammatic side view corresponding to Figure 3, and illustrating the twoheight method of measurement; Figure 5 is an enlarged view of part of Figure 4, illustrating a typical two-head angle measuring instrument; and Figure 6 is a view similar to Figure 4 showing the measuring instrument being used to view an adjacent marker.

Referring firstly to Figures 1 and 2, there is shown a section of a single three-lane carriageway forming part of a motorway to be surveyed. As shown in Figure 2, the road surface 1 slopes gently downwards from the central reservation crash barrier 2 to the outer edge. The lines 3 to 7 represent white lines applied to the road surface to delineate the individual parts of the carriageway, those illustrated being to the conventional British pattern: solid lines 3,4 being the outer and inner hard shoulder markers; broken lines 5,6 separating and defining the three lanes on the main road surface; and solid line 7 defining the inner edge of the carriageway.

All of the lines can be used to define, in association with spaced laterally-extending measurement lines, a series of measurement points 8,9 at which sets of level measurements are taken. The spacing between points 8 and 9 in the direction of the carriageway will be dictated by the specification of the survey.

The method of the invention involves initially installing along the carriageway a series of spacedapart height markers. Referring to Figure 3, a section of straight carriageway shows the installation of three of these markers 10, 11 and 12 which, in the arrangement illustrated, are equally spaced apart by the required measurement distance, for example 10 metres. The markers do not, however, have to be equally spaced; for example, it may be more convenient to position the markers at points opposite the position of the "solid" parts of broken white lines, since this is more convenient and quicker for observing the section. In any event, following installation, the markers are co-ordinated both for position and height by known methods. The markers are positioned just inboard of the line 3 marking the outer edge of the hard shoulder.The surveying method proceeds with the taking of a number of identical measurements at each of these markers in turn along the road. By way of illustration, the measurements to be taken at one of these markers, marker 11, will now be described.

First, in order to obtain the required bearing of a notional measurement line 18, each of the adjacent markers 10 and 12 are sighted in turn to obtain the horizontal angle subtended between the notional lines 13,14 joining the respective markers 10 and 12 to the marker 11. In the case of the straight carriageway illustrated, this angle will, of course, be approximately 180 . It will be apparent to those skilled in the art that the bearing of line 18 could be obtained by other methods.

It is next necessary to make vertical angle measurements at each of a number of points 15, 16, 17 at which the lines 4, 5 and 6 respectively cross the notional measurement line 18 which extends transversely across the carriageway. The notional line 18 is generally obtained by bisecting the angle a, using the horizontal angle measurements of the adjacent markers 10,12. Thus, in the case of the straight carriageway, the line 18 extends across at right angles to the carriageway direction. However, other angles across the carriageway may be used if appropriate.

A diagrammatic side view of the arrangement used to make the measurements at each marker is illustrated in Figures 4 and 5. The measurements are taken by an angle measuring instrument 19 which contains a pair of vertically-spaced theodolites 20,21. The theodolites 20,21 are positioned vertically above the marker 11 and are a known height above the datum level defined by the top surface of the marker, which is conveniently the same height as the surrounding road surface. In an alternative instrument 19 (not shown) a single theodolite is vertically movable between the positions occupied by theodolites 20 and 21.

After setting the two theodolites up to take measurements along the notional line 18 (Figure 3), a series of vertical angle measurements are taken: for each height, a measurement is taken at each point 15, 16, 17 and so on across the carriageway. The manner of sighting using a theodolite is well known, and will not be described in detail. Figure 4 illustrates the sighting of just a single point, for example point 15, but the principle is the same for the other points, 16, 17 etc.

By this means, a series of vertical angle measurements are obtained at each height - these angles are illustrated in Figure 5 as e for the upper theodolite 20 and O for the lower theodolite 21.

From these measurements the height H of each measurement point relative to marker 11, and its distance D along line 18 from line 11 can be computed by known techniques. Thus, the position and height of each measurement point is accurately established and this information can be utilised in a variety of ways.

Typically the distance d from the marker 11 (and all other markers) to the line 3 marking the outer edge of the hard shoulder is approximately 0.05 m.

It will be appreciated that the accuracy of the measurements is dependent upon knowing accurately the value of certain fixed parameters. In particular, the vertical distance between the theodolites 20 and 21 has a critical effect on accuracy. Thus, in an extension to the abovedescribed method, we can use the known distance between adjacent markers (known from the previouslyperformed co-ordination of all the markers - see above) as a quality control procedure to obtain a fine accuracy in the height difference measurement, conventionally taken for example with a tape measure, of the two theodolites 20 and 21.

This is shown in Figure 6. In Figure 6, the theodolites are shown turned through a horizontal angle of about 90 to check the adjacent marker 12.

The marker 12 may or may not be at the same height as marker 11, and this possible height difference is represented by the letter T.

Sightings are now made using theodolites 20 and 21, in the same manner as discussed above, to obtain the vertical angles e and O representative of the distance E of marker 12 from marker 11. The vertical distance F, as measured in the conventional manner between the two theodolites is then measured to enable the distance E to be calculated.

The two angles e and O can be assumed to be accurate and therefore any discrepancy between the distance E, as calculated from angles e and , and the distance E as known from the co-ordination will be as a result of inaccuracies in the measurement of distance F. Since the distance between markers 11 and 12 from the co-ordination can be relied upon to be accurate, the result of measurements taken by the arrangement illustrated in Figure 6 can be used to correct the value of F. Thus, if these measurements are taken before the main sightings across the carriageway, then the corrected value of F can be used for enhanced accuracy.This is achieved by placing the corrected value of F in the associated computer programme as a parameter for the subsequent calculation of road surface measurements at points 15, 16, 17 and so on.

It would also be possible to routinely carry out the sightings illustrated in Figure 6 at each marker 10, 11, 12 etc., to a single adjacent coordinated marker, in order to derive, without the necessity for physical measurement, the vertical distance F between the theodolites 20 and 21. Such measurements at each marker would be taken prior to taking the roadway measurements at that marker, and would enable the critical parameter F to be set with accuracy prior to the main roadway measurements being taken.

It will be realised that the various distances and similar details given above are by way of example only; generally when a survey is commissioned, such details will be specified, and the survey team will have to work to them. The above-described method readily achieves the accuracy normally required for this type of survey.

Claims (14)

1. A method of road surveying comprising installing a series of spaced-apart height reference markers along the route of a road to be surveyed, placing an angle measuring instrument over each marker in turn and taking, at each reference marker, a series of vertical angular measurements of selected spaced points lying along a notional line extending from the reference marker and transversely across the road therefrom, said measurements comprising: 1) a first series of measurements at a first height above the reference marker; and 2) a second series of measurements at a second height above the reference marker, said second height being different from the first.

2. A method as claimed in claim 1 further comprising taking further measurements, at each marker, of the horizontal angle of the two next adjacent markers on either side of the current marker.

3. A method as claimed in claim 2 wherein said notional line is such as to bisect said horizontal angle.

4. A method as claimed in any one of claims 1, 2 or 3, further comprising calculating the distance and height of each point with respect to the reference marker from a knowledge of the first and second heights and, for each point, the two vertical angular measurements.

5. A method as claimed in claim 4 further comprising taking preliminary measurements, at each reference marker, of the vertical angle at a first and a second height above said marker, of at least one of the next adjacent reference markers on either side of the current marker in order to enable the distance to the adjacent marker to be calculated.

6. A method as claimed in claim 5 wherein the distance between adjacent reference markers is already known accurately by previously-taken measurements, said method including using the calculated distance between the reference markers, if different from the previously-measured distance, to correct or set the measurement of the vertical distance between said first height and said second height, which corrected distance is used for the distance and height calculations associated with each of said points along said notional line extending across the road.

7. A method as claimed in any one of the preceding claims wherein said angle measuring instrument is moved from one of said heights to the other of said heights between said first and said second series of measurements.

8. A system for road surveying, said system comprising: a plurality of height reference markers each having means whereby they may be positioned along the route of a road surface to be surveyed and means to define a height datum with respect to the surrounding road surface; and An angle measuring instrument comprising first and second vertical angle measuring means, and support means for supporting said first and second vertical angle measuring means at respective first and second heights above the height datum defined by a said reference marker.

9. A system as claimed in claim 8 wherein each of said vertical angle measuring means comprises a separate instrument positioned at different heights above the datum.

10. A system as claimed in claim 8 wherein the first and second angle measuring means comprises a single instrument, and wherein means are provided for moving the instrument from said first height to said second height and vice versa.

11. A system as claimed in any one of claims 8 to 10 wherein each said reference marker comprises means whereby it may be positioned at a desired position, together with a surface defining said datum.

12. A system as claimed in claim 11 wherein said positioning means comprises a peg which may be inserted in the ground.

13. A system as claimed in any one of the preceding claims wherein the or each vertical angle measuring means comprises a theodolite.

14. A system for road surveying substantially as hereinbefore described with reference to the accompanying drawings.