Locating arrangement and method using boring tool and cable locating signals
An arrangement and an associated method are described in which a boring tool is moved through the ground within a given region along a path in which region a cable is buried. The boring tool and the cable transmit a boring tool locating signal and a cable locating signal, respectively. Intensities of the boring tool locating signal and the cable locating signal are measured along with a pitch orientation of the boring tool. Using the measured intensities and established pitch orientation, a positional relationship is determined to relative scale including at least the boring tool and the cable in the region. The positional relationship is displayed to scale in one view. The positional relationship may be determined and displayed including the forward locate point in scaled relation to the boring tool and the cable. Cable depth determination techniques are described including a two-point ground depth determination method.
1. In a region which includes at least one generally straight inground cable extending across said region, from which cable a locating signal is transmitted, a method comprising the steps of:
measuring a local flux intensity, including three orthogonally opposed values, of the locating signal at an above ground point within said region using a portable locator; and
using the local flux intensity to establish an approximate horizontal distance to the cable based on a vertically oriented component of the locating signal at the above ground point determined from the local flux intensity and a horizontally oriented component of the locating signal at the above ground point determined from the local flux intensity, which horizontally oriented component is generally normal to the cable in a plan view and represents a total flux intensity in a horizontal plane.
2. The method of claim 1 wherein the vertically oriented component of the locating signal is denoted as b w and the horizontally oriented component of the locating signal is denoted as b h and wherein the approximate horizontal distance is estimated based on an angle α determined by the expression:
tan
α
=
b
w
b
h
.
3. The method of claim 2 wherein the locator includes an axis of symmetry and wherein b h is given by
b
h
=
b
u
1
+
(
b
v
b
u
)
2
where b u is measured along the axis of symmetry of the locator with the axis of symmetry horizontally oriented and b v is measured horizontally normal thereto.
4. The method of claim 2 wherein tan α includes a sign and said method includes the step of using the sign of α to establish whether the cable is ahead of or behind the locator.
5. The method of claim 2 further comprising the step of determining an angle γ between a direction that is normal to the cable in a plan view and the locating direction given by the expression
tan
γ
=
b
v
b
u
such that γ establishes a relative direction of the cable from the locator at the above ground point with the locator oriented in the locating direction.
6. The method of claim 5 wherein said locator includes a display and wherein said method further comprises the step of displaying a positional relationship between the locator, oriented along said locating direction at the above ground point, and the cable based on γ and α.
7. In a system for use in a region which includes at least one generally straight inground cable extending across said region, from which cable a locating signal is transmitted a locator comprising:
a first arrangement for measuring a local flux intensity, including three orthogonally opposed values, of the locating signal at an above ground point;
a processing arrangement for using the local flux intensity to establish an approximate horizontal distance to the cable in a plan view based on a vertically oriented component of the locating signal at the above ground point determined from the local flux intensity and a horizontally oriented component of the locating signal at the above ground point determined from the local flux intensity, which horizontally oriented component is generally normal to the cable in a plan view and represents a total flux intensity in a horizontal plane.
8. The locator of claim 7 wherein the vertically oriented component of the locating signal is denoted as b w and the horizontally oriented component of the locating signal is denoted as b h and wherein the processing arrangement is configured for estimating the approximate horizontal distance based on an angle α determined by the expression:
tan
α
=
b
w
b
h
.
9. The locator of claim 8 including an axis of symmetry and wherein the processing arrangement is configured for determining b h using the expression
b
h
=
b
u
1
+
(
b
v
b
u
)
2
where b u is measured along the axis of symmetry of the locator with the axis of symmetry horizontally oriented and b v is measured horizontally normal thereto.
10. The locator of claim 8 wherein the processing arrangement is configured for determining a sign of tan α and for using the sign of α to establish whether the cable is ahead of or behind the locator.
11. The locator of claim 8 wherein the processing arrangement is configured for determining an angle γ between a direction that is normal to the cable in a plan view and the locating direction given by the expression
tan
γ
=
b
v
b
u
such that γ establishes a relative direction of the cable from the locator at the above ground point with the locator oriented in the locating direction.
12. The locator of claim 11 including a display and wherein said processing arrangement is configured for determining a positional relationship based on γ and α for presentation on said display, said positional relationship including the locator oriented along said locating direction at the above ground point and the cable in a plan view.