Sensor calibration

Abstract

A method of calibrating a vehicle interior sensor (122, 124) comprising installing in the interior (102) of the vehicle (100) a temporary reference device (130), the temporary reference device (130) being a stand-alone device and comprising a reference feature (134, 142) detectable by the vehicle interior sensor (122, 124). The temporary reference device (130) is arranged to be installed by interfacing with a part of the vehicle interior (114) to locate the temporary reference device (130), and thereby locating the reference feature (134, 142) at a known position within the interior (102) of the vehicle (100). The method further comprises using the vehicle interior sensor (122, 124) to acquire sensed data indicative of the position of the reference feature (134, 142) according to the vehicle interior sensor (122, 124). Still further, the method comprises calibrating the vehicle interior sensor (122, 124) in accordance with any discrepancy between the known position of the reference feature (134, 142) and the position of the reference feature (134, 142) indicated by the sensed data.

Description

TECHNICAL FIELD The present disclosure relates to a sensor calibration. Aspects of the invention relate to a method of calibrating a vehicle interior sensor, to a temporarily installable reference device and to a system. BACKGROUND Vehicles are known to incorporate various interior sensors. Where these sensors are used for tasks such as occupant detection, occupant position detection, occupant identification and / or occupant monitoring, they are typically sensitive to their own installation position within the vehicle interior in terms of the accuracy of data collected / analysis performed. Difficulty is however often encountered in sufficiently reliably and accurately positioning such sensors during installation / maintenance. Consequently, attempts are made to calibrate such sensors fortheir installed position. An example of a method used to achieve calibration is to temporarily position a radiation reflector within the interior of the vehicle. This is located accurately by a robot arm at a known, pre-determined position relative to a vehicle frame of reference. The sensor can then be used to detect the radiation reflector and calibrate its own installation position based on the detected position of the radiation reflector and the known accurate positional information for that radiation reflector. This approach has various drawbacks. It is relatively costly, requiring robotised task completion. There is the need for careful operation of the robot arm to avoid damage to operators and / or the vehicle. Still further, it can be difficult to maintain positioning of the radiation reflector to the desired level of accuracy (e.g. as normal wear occurs to the robot). It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide a vehicle interior sensor, a temporarily installable reference device, and a system as claimed in the appended claims. According to an aspect of the present invention there is provided a method of calibrating a vehicle interior sensor comprising: installing in the interior of the vehicle a temporary reference device, the temporary reference device being a stand-alone device and comprising a reference feature detectable by the vehicle interior sensor, the temporary reference device being arranged to be installed by interfacing with a part of the vehicle interior to locate the temporary reference device, and thereby locate the reference feature at a known position within the interior of the vehicle; using the vehicle interior sensor to acquire sensed data indicative of the position of the reference feature according to the vehicle interior sensor; calibrating the vehicle interior sensor in accordance with any discrepancy between the known position of the reference feature and the position of the reference feature indicated by the sensed data. The vehicle interior sensor may be some form of scanning / radiation (e.g. radio, optical laser, infrared etc) based sensor. Further, it may be sensitive to its own installation position in terms of the accuracy of data collected and / or analysis performed based thereon. Specifically, the vehicle interior sensor may measure or detect position relative to a frame of reference (e.g. a vehicle frame of reference). If therefore the vehicle interior sensor is not installed at its nominal position, it may provide inaccurate data. Further, relatively small deviations from the nominal position may result in significant errors in the data. The vehicle interior sensor may for instance be used to make relatively fine iocational / positional judgements and relatively small discrepancies in installation position may prejudice this. This difficulty may be particularly acute where for instance the positional error is angular (the error then increasing at ever increasing distance from the vehicle interior sensor). Example errors / misalignments in the positional installation of the vehicle interior sensor include translational position errors in one, two orthree dimensions (e.g. x, y and z) and / or angular position errors (e.g. in at least one of pitch, yaw and roll). The arrangement of the temporary reference device to interface with the part of the vehicle interior may be a specific adaptation to interface with a specific part / feature of the vehicle interior. The temporary reference device may for instance be shaped to compliment the feature and / or to otherwise cooperate with it and / or slot into it and / or be designed to be attached or attach itself to it and / or be secured or secure itself to it. In particular, the temporary reference device and the part of the vehicle interior may, between them, provide male and female parts arranged to engage one another or other complimentary engaging and / or securing formations. With the installation being made by the interface, the temporary reference device may offer a solution to calibrating the vehicle interior sensor for its installed position. It may for instance take advantage of a vehicle interior part having a known position to which the temporary reference device can be interfaced (e.g. secured) in a manner giving a reliable known position. Approaching calibration in this way may offer advantages in terns of reliability and repeatability of the calibration technique. Additionally, especially given the stand-alone nature of the temporary reference device, it may be that fewer safety / damage provisions are necessary by comparison with alternatives, e.g. automated positioning of a radiation reflector (e.g. corner reflector) inside the vehicle using a robot arm. Additionally, the solution may be considered relatively easy and / or inexpensive. The vehicle itself may be a land vehicle and / or a road vehicle. In particular the vehicle may be a passenger vehicle and / or a car. The vehicle sensor may be arranged to monitor all or part of a passenger cabin of the vehicle. The part of the vehicle may be located in the passenger cabin of the vehicle. According to another aspect of the present invention there is provided a method of calibrating a vehicle interior sensor for its installation position inside a vehicle comprising: installing in the interior of the vehicle a temporary reference device, the temporary reference device being a stand-alone device and comprising a reference feature detectable by the vehicle interior sensor, the temporary reference device being arranged to be installed by interfacing with a part of the vehicle interior to locate the temporary reference device, and thereby locating the reference feature at a known position within the interior of the vehicle; using the vehicle interior sensor to acquire sensed data indicative of the position of the reference feature according to the vehicle interior sensor given its installed position: calibrating the vehicle interior sensor for its installation position in accordance with any discrepancy between the known position of the reference feature and the position of the reference feature indicated by the sensed data. According to yet another aspect of the present invention there is provided a method of calibrating a vehicle interior sensor comprising: installing in the interior of the vehicle a temporary reference device, the temporary reference device comprising a reference feature detectable by the vehicle interior sensor and the temporary reference device being arranged to be installed by interfacing with a part of the vehicle interior; using the vehicle interior sensor to acquire sensed data indicative of the position of the reference feature according to the vehicle interior sensor; calibrating the vehicle interior sensor in accordance with any discrepancy between the known position of the reference feature and the position of the reference feature indicated by the sensed data. In some embodiments the vehicle interior sensor comprises a radar system and the method comprises calibrating the radar system in accordance with any discrepancy between the known position of the reference feature and the position of the reference feature indicated by the sensed data. The radar system may comprise one or both of a radar transmitter and a radar receiver. The radar system may be a continuous wave radar system. The radar system may be used for determining the presence / position within the vehicle interior of occupants and / or other objects. The collected data may be used in controlling vehicle features. The radar system may for instance be used to discriminate between types of occupant (e.g. adult or child). Such radar systems, while potentially very useful, may be both prone to installation error in terms of position and installation position sensitive in terms of the accuracy of their sensed data. Such systems may therefore be suitable candidates in terms of benefiting from the method. In some embodiments the method comprises moving the reference feature with a direction component towards and / or away from the vehicle interior sensor during acquiring the sensed data. The reference feature may therefore be considered arranged to be capable of returning a doppler signal or as a doppler generating target. This feature may aid with detection (e.g. filtering a background signal) where for instance the sensor comprises a radar system. The movement may be battery powered. There may for instance be a battery in the temporary reference device aiding portability and ease of use. In some embodiments the reference feature rotates during acquiring the sensor data. This may be a convenient way of creating a doppler generating target. The reference feature may for instance be a fan or similar body. Alternatives are also possible however e.g. a vibrating body. In some embodiments the vehicle interior sensor comprises an electromagnetic sensor system and the method comprises calibrating the electromagnetic sensor system in accordance with any discrepancy between the known position of the reference feature and the position of the reference feature indicated by the sensed data. The electromagnetic sensor system may comprise one or both of an electromagnetic transmitter and an electromagnetic receiver. The electromagnetic sensor system may for instance use visual and / or infrared and / or ultraviolet radiation and may for instance be a camera. The electromagnetic sensor system may be used for determining the presence / position within the vehicle interior of occupants and / or other objects. It may additionally or alternatively be used for occupant monitoring. The collected data may be used in controlling vehicle features. The electromagnetic sensor system may for instance be used to discriminate between types of occupant, (e.g. adult or child). Such electromagnetic sensor systems, while potentially very useful, may be both prone to installation error in terms of position and installation position sensitive in terms of the accuracy of their sensed data. Such systems may therefore be suitable candidates in terms of benefiting from the method. In some embodiments the reference feature provides an electromagnetic contrast detected by the electromagnetic sensor system during acquiring the sensor signal. The electromagnetic contrast may be with respect to a surrounding area of the temporary reference device and / or an area of the interior of the vehicle which would provide a background to the reference feature when viewed from the electromagnetic sensor system. It may be for instance that the electromagnetic contrast is provided by colour difference or a fluorescent coating. in some embodiments the method comprises providing reference data indicative of the position of the reference feature within the interior of the vehicle when the temporary reference device is interfaced with the part of the vehicie interior. This may be the means by which the position of the reference feature is known. The data provided may for instance have been derived from a simulation / model of the vehicle type and / or a simulation / model specific to the unique vehicle in which the calibration is being performed. The reference data may provide accurate data for the location of the part of the vehicle interior, allowing determination of the position of the reference feature. Alternatively, it may provide the position of the temporary reference device and / or the position of the reference feature assuming that the temporary reference device is interfaced with the part of the vehicle. In some embodiments the method comprises interfacing the temporary reference device with the part of the vehicle interior by hand. This may be a convenient and / or quick way of installing the temporary reference device and / or may require fewer safety considerations than alternatives e.g. using a robot arm. These advantages may arise as a result of there being no need for specific installation equipment, which might be heavy and / or require additional safety considerations. Installation and / or extraction may specifically be a non-automated process. The temporary reference feature may be hand-portable, which may ease transportation between vehicles and allow for personal carrying for convenience. The interfacing may be performed by the user attaching and / or slotting and / or securing the temporary reference device to the part of the vehicle interior (which could for instance be a cupholder.) The method may also comprise removing the temporary reference device upon completion of the calibration. In some embodiments the part of the vehicle interior is within a field of view of the vehicle interior sensor. This may simplify the process and / or apparatus required to perform the calibration. The part of the vehicle interior may be positioned in and / or on a centre console (front or rear) and / or transmission tunnel of the vehicle. The part of the vehicle interior may be positioned to be associated with a front or rear row of seats. The vehicle interior sensor itself may be positioned substantially above the rear seats and / or boot, or substantially above the front seats and / or dashboard. The vehicle interior sensor may be substantially centrally aligned between near and offsides of the vehicle. In some embodiments the part of the vehicle interior is a non-repositionable part. The part of the vehicle interior may therefore be considered static, fixed, non-adjustable and / or immovable. This may aid in terms of the reliability of the position of the part of the vehicle interior and therefore the position of the temporary reference device when interfaced with the part of the vehicle. in some embodiments the part of the vehicle interior is a cupholder. This may be advantageous because a cupholder may typically be non-repositionable and within the required field of view when for instance in the centre console. A cupholder may also provide a natural means to accurateiy and / or repeatably and / or securely position the temporary reference device. Alternatives are possible however, for instance a hand-brake lever or vehicle interface control knob. in some embodiments the temporary reference device comprises a base portion shaped to be receivable by the cupholder. The base portion may for instance be cup like in shape and / or form. The base portion may assist with accurate locating of the temporary reference device. The base portion may be arranged to close-fit or interfere nee-fit the cupholder, thereby improving the predictability and accuracy of its position when interfaced. In some embodiments multiple vehicle interior sensors are calibrated fortheir respective installation positions inside of the vehicle using the temporary reference device once installed. This may be advantageous in terms of efficiency and convenience in that multiple vehicle interior sensors may be calibrated using a single method requiring only a single installation of the temporary reference device. Additionally, it may be advantageous because the multiple sensors may then work from a common calibrated frame of reference and so more easily communicate and / or their sensor outputs be more readily combined / compared. It may be for instance that a radar system and an electromagnetic sensor system (as previously described) are calibrated in this way. The reference feature may be common to the vehicle interior sensors or the temporary reference device may comprise multiple reference features each corresponding to one or more of the vehicle interior sensors (e.g. the temporary reference device may comprise both a fan and a detectable electromagnetic contrast). Where such multiple vehicle interior sensors are provided and calibrated together in this manner, they may be used for common functions / determinations (for instance being used at least in part to corroborate and / or check data and or conclusions from data generated by the respective vehicle interior sensors). According to yet another aspect of the present invention there is provided a temporarily installable reference device arranged to be installed in the interior of a vehicle for the calibration of a vehicle interior sensor of the vehicle, the calibration being for the installation position inside of the vehicle of the vehicle interior sensor, the temporary reference device being a stand-alone device and comprising a reference feature detectable by the vehicle interior sensor, the temporary reference device being arranged to be installed by interfacing with a part of the vehicle interior to locate the temporary reference device, and thereby locate the reference feature at a known position within the interior of the vehicle. in some embodiments the vehicle interior sensor comprises a radar system. in some embodiments the reference feature is arranged to move in a manner having a direction component towards and / or away from the vehicle interior sensor. in some embodiments the reference feature is a body arranged to rotate. in some embodiments the vehicle interior sensor comprises an electromagnetic sensor system. in some embodiments the reference feature is arranged to provide an electromagnetic contrast detectable by the electromagnetic sensor system. in some embodiments the temporary reference device is arranged to be interfaced with the part of the vehicle interior by hand. In some embodiments the part of the vehicle interior is a non-repositionabie part. In some embodiments the part of the vehicle interior is a cupholder. In some embodiments the temporary reference device comprises a base portion shaped to be receivable by the cuphoider. In some embodiments the temporary reference device is arranged for the calibration of multiple vehicle interior sensors fortheir respective installation positions inside of the vehicle. According to a further aspect of the present invention there is provided a system comprising the temporarily installable reference device as previously described and a vehicle comprising the vehicle interior sensor and the part of the vehicle interior as previously described. In some embodiments the method comprises providing reference data indicative of the position of the reference feature within the interior of the vehicle when the temporary reference device is interfaced with the part of the vehicle interior. In some embodiments the part of the vehicle interior is within a field of view of the vehicle interior sensor. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, ail embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a vehicle according to an embodiment of the invention; Figure 2 shows a top view of a vehicle interior according to an embodiment of the invention; Figure 3 shows a perspective view of the interior of a vehicle according to an embodiment of the invention; Figure 4a shows a front perspective view of a temporary reference device according to an embodiment of the invention; Figure 4b shows a rear perspective view of the temporary reference device of Figure 4a according to an embodiment of the invention; and Figure 5 shows a flow chart of a method of calibrating a vehicle interior sensor according to an embodiment of the invention. DETAILED DESCRIPTION A system in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figures 1 to 4. The system includes a vehicle generally shown at 100 which in this case is a car. A simplified top view of an interior 102 (in this case a passenger cabin) of the vehicle 100 is shown in Figure 2. The interior 102 has front 104 and rear 106 rows of seats. The front row of seats 104 has two discrete seats, a driver seat 108 and a front passenger seat 110 to respective sides of the interior 102. The driver 108 and passenger 110 seats are separated by a centre console 112. The centre console 112 includes a cupholder 114 rebated into the centre console. The cupholder 114 is substantially centrally aligned with respect to the vehicle 100. The cupholder is non-repositionable and its location within the interior 102 therefore remains fixed relative to a vehicle frame of reference. The rear row of seats 106 has left 116 and right 118 seats to respective sides of the interior 102 and a centre seat 120 between them. The interior 102 has two vehicle interior sensors: a radar system 122 and an electromagnetic sensor system 124. The radar system 122 is a continuous wave radar system with a radar transmitter and radar receiver located in a pod on the ceiling of the interior 102. The pod is substantially above the rear row of seats 106 and centrally aligned with respect the vehicle. The radar system is used for determining the presence / position within the interior 102 of occupants and / or other objects relative to the vehicle frame of reference. The electromagnetic sensor system 124 is a visual spectrum camera used for occupant monitoring relative to the vehicle frame of reference. It might for instance be used for occupant classification (e.g. into categories such as adult and child). The visual spectrum camera is integrated into a dashboard of the interior 102, forward of the front row of seats 104. A field of view of the visual spectrum camera faces rearwards within the interior 102. The cupholder 114 is within the unimpeded respective fields of view of both the radar system 122 and the electromagnetic sensor system 124. That is, both have a direct line of sight to the cupholder 114. Further, the cupholder 114 is located relatively near to the centre of the field of view of the radar system 122 and the electromagnetic sensor system 124. Consequently, the cupholder 114 is in a higher sensitivity and accuracy portion of the respective fields of view. The field of view of the radar system 122 is shown at 126 in Figure 3 and generally faces forwards and downwards within the interior 102. The radar system 122 and electromagnetic sensor system 124 installation processes within the interior 102 are subject to a degree of positional error with respect to respective nominal installation positions. This can lead to errors in the fields of view of the radar system 122 and / or electromagnetic sensor system 124 as compared with expectation relative to the vehicle frame of reference. This in turn can lead to inaccurate position based assessments as performed by the radar system 122 and electromagnetic sensor system 124. it might for instance be that an occupant is assessed as being in a particular location within the vehicle (e.g. occupying a particular one of the seats 108, 110, 116, 118,120) when in fact the occupant is not in that seat and may for instance be in another of the seats 108,110,116,118,120. Such an error might for instance be caused by an installation error in the yaw direction. By way of further example, positional installation error could lead to an erroneous assessment as to whether or not a particular passenger is a child or an adult, in accordance with a height assessment of that occupant relative to the vehicle frame of reference. Such an error might for instance be caused by an installation error in the yaw pitch direction. In view of the potential forthe positional errors discussed, calibration methods used for the radar system 122 and the electromagnetic sensor system 124 are hereby described. The calibration methods utilise a temporary reference device 130 (shown in Figure 4) which forms part of the system. The temporary reference device 130 is temporary in the sense that it is envisaged that it will be positioned in the interior 102 for the purposes of the calibration and then removed again. The temporary reference device 130 is therefore arranged to be readily and selectively engaged with and disengaged from a part of the vehicle interior (in this case the cupholder 114). The temporary reference device 130 has a base portion 132 shaped and sized to fit into the cupholder 114 in a relatively tight fit. Specifically, the base portion 132 is similarly shaped and sized to the cupholder 114. The form of the base portion 132 constitutes a specific adaptation of the temporary reference device 130 for It to interface with the cupholder 114. The temporary reference device 130 also has a fan 134 as an instance of a reference feature. The fan 134 is actuatable to rotate its blades via a power button on a stem portion 136 of the temporary reference device 130. The stem portion 136 is located between the base portion 132 and a fan portion 138 which includes the fan 134. Rotation of the fan 134 is powered by a battery located in the base portion 132. The rotating fan 134 provides a doppler generating target forthe radar system 122 as discussed further below. The fan portion 138 has a rear wall with a rearward facing surface 140. The rearward facing surface 140 constitutes an electromagnetic contrast. 142, which is a further instance of a reference feature of the temporary-reference device 130. In this case, the electromagnetic, contrast 142 is a specific colouration that contrasts with the colouration of adjacent portions of the temporary reference device 130 and with parts of the interior 102 in substantially the same line of sight as the temporary reference device 130 as viewed from the visual spectrum camera 124. In this case, the colouration of the electromagnetic contrast is red (that is the rearward facing surface 140 is coloured red), whilst the adjacent portions of the temporary reference device 130 are black. Additionally, the electromagnetic contrast 142 is provided with a specific form in shape that may be more readily recognised by image recognition software. In this case the rearward facing surface 140 (and correspondingly the electromagnetic contrast) are circular. However, other shapes that are readily recognised by image recognition software are also possible (e.g. a square). The electromagnetic contrast 142 provides an optically recognisable target for the electromagnetic sensor system 124 as discussed further below. With the base portion 132 engaged in the cupholder 114, the temporary reference device 130 is retained in an upright position with the stem portion 136 and fan portion 138 protruding, substantially vertically, from the cupholder 114. With the temporary reference device 130 thus interfaced with the interior 102, it is located at a specific position within the interior 102. Furthermore, this position is known given the known characteristics of the temporary reference device 130 (i.e. form and dimensions) and given the availability of a model of the interior 102 specific to the vehicle 100 (as contrasted with the vehicle type). The model details the position of various features, including the cupholder 114, in the vehicle frame of reference. The temporary reference device 130 is a stand-alone device. It is therefore independent and not for instance arranged for use with a deploying system such as a robot. The temporary reference device 130 is instead a hand-portable, battery powered device. The temporary reference device 130 is also arranged to be handportable, hand deployable and hand removable in terms of being interfaced and removed from the cupholder 114. in accordance with a calibration method for the radar system 122, a setup step 150 is conducted. In the setup step 150, an operator interfaces the base portion 132 of the temporary reference device 130 with the cupholder 114 by hand. In addition, the setup step 150 also includes the operator connecting a tester with a diagnostics port of the vehicle 100. The tester stores reference data indicative of the position of the cupholder and therefore the fan 134 and electromagnetic contrast 142 in accordance with a pre-determined 3D model of the vehicle 100. In an acquisition step 152, the tester sends a signal to the diagnostics port via the connection, the signal providing the reference data indicative of the position of the fan 134. This signal is received from the diagnostics port by an electronic control unit (ECU) of the vehicle 100 and relayed to the radar system 122. As will be appreciated however, in other embodiments the tester function might be achieved with integrated software or the tester might communicate directly with the radar system 122. In such cases, the relevant parts of the setup 150 and acquisition 152 steps may be adjusted or omitted as appropriate. In a sensing step 154, the radar system 122 operates (including transmission and reception of radar signals) to acquire sensed data indicative of the position of the fan 134. This is aided by activation of the fan 134 so that its blades rotate, thereby presenting a doppler generating target to the radar system 122, In this manner, detection of the fan 134 is made more reliable / more accurate in view of easier filtering of a background signal radar return. In a calibration step 156, the radar system 122 compares the position of the fan 134 according to the sensed data, with the position of the fan 134 according to the model data. Any discrepancy between the two indicates to the radar system 122 the error caused by its deviation in its installation position from nominal. In a storage step 158, the radar system 122 stores data indicating the error caused by its deviation in its installation position from nominal. This is used in future operation of the radar system 122 to modify the direction of the transmitted radar beam to coincide with the direction of the transmitted radar beam had the radar system 122 been installed with nominal positioning. Thus is achieved by modifying the transmitted radar beam with a phase change of a transmission wave in a waveguide antenna of the radar system 122. Consequently, no mechanical adjustment of the radar system 122 is required. In a feedback step 160, the radar system 122 sends a signal with feedback data indicating the Installation position of the radar system 122, determined in accordance with the discrepancy, to the ECU. The ECU relays this to the tester, which outputs it on a display of the tester. In this manner the operator or another user is able to receive feedback as regards the installation position of the radar system 122. In a completion step 162, the operator deactivates the rotation of the blades of the fan 134 (thereby preserving the life of the battery), disconnects the tester from the diagnostics port and removes the temporary reference device 130 and tester from the vehicle 100. The method may be repeated for another vehicle (be this in a vehicle manufacturing setting or a service setting). As will be appreciated, a similar method may be employed, mutatis mutandis, to calibrate the electromagnetic sensor system 124. The method for calibrating the electromagnetic sensor system 124 may proceed in a similar manner, but with the reference data acquired from the tester and the sensed data by the electromagnetic sensor system 124 being for / of the electromagnetic contrast 142. The acquisition of the sensed data may be by capturing a stili or moving image of the temporary reference device 130 including the electromagnetic contrast 142. This may be followed by image recognition processing (i.e. target detection) to recognise the electromagnetic contrast 142 and determine its position in accordance with the sensed data. This determined position can then be compared with the known position in accordance with the reference data to determine the positional error of the eleotromagnetic sensor system 124 with respect to the nominal installation position, in future therefore, data sensed by the electromagnetic sensor system 124 can be adjusted to account for this error (e.g. parameters of a captured image can be adjusted according to any misalignment determined during the calibration). This may be performed as an alternative to or in addition to the calibration of the radar system 122. Where performed in addition to the calibration of the radar system 122, it may be performed simultaneously or sequentially with the method for calibrating the radar system 122. The simultaneous option may be facilitated by the electromagnetic contrast 142 being visible from an opposite side (e.g. rear side) of the temporary reference device to the fan 134. It will be appreciated that various changes and modifications can be made to the present invention without 5 departing from the scope of the present application.

Claims

1. A method of calibrating a vehicle interior sensor comprising:installing in the interior of the vehicle a temporary reference device, the temporary reference device being a stand-alone device and comprising a reference feature detectable by the vehicle interior sensor, the temporary reference device being arranged to be installed by interfacing with a part of the vehicle interior to iocate the temporary reference device, and thereby locating the reference feature at a known position within the interior of the vehicle;using the vehicle interior sensor to acquire sensed data indicative of the position of the reference feature according to the vehicle interior sensor;calibrating the vehicle interior sensor in accordance with any discrepancy between the known position of the reference feature and the position of the reference feature indicated by the sensed data.

2. A method according to claim 1 where the vehicle interior sensor comprises a radar system and the method comprises calibrating the radar system in accordance with any discrepancy between the known position of the reference feature and the position of the reference feature indicated by the sensed data.

3. A method according to any preceding claim where the method comprises moving the reference feature with a direction component towards and / or away from the vehicle interior sensor during acquiring the sensed data.

4. A method according to any preceding claim where the reference feature rotates during acquiring the sensor data.

5. A method according to claim 1 where the vehicle interior sensor comprises an electromagnetic sensor system and the method comprises calibrating the electromagnetic sensor system in accordance with any discrepancy between the known position of the reference feature and the position of the reference feature indicated by the sensed data.

6. A method according to claim 5 where the reference feature provides an electromagnetic contrast detected by the electromagnetic sensor system during acquiring the sensor signal.

7. The method according to any preceding claim comprising providing reference data indicative of the position of the reference feature within the interior of the vehicle when the temporary reference device is interfaced with the part of the vehicle interior.

8. The method according to any preceding claim comprising interfacing the temporary reference device with the part of the vehicle interior by hand.

9. The method according to any preceding claim where the part of the vehicle interior is within a field of view of the vehicle interior sensor.

10. The method according to any preceding claim where the part of the vehicle interior is a non-repositionable part.

11. The method according to any preceding claim where the part of the vehicle interior is a cupholder.

12. The method according to claim 11 where the temporary reference device comprises a base portion shaped to be receivable by the cupholder.

13. A method according to any preceding claim where multiple vehicle interior sensors are calibrated for their respective installation positions inside of the vehicle using the temporary reference device once installed.

14. A temporarily installable reference device arranged to be installed in the interior of a vehicle for the calibration of a vehicle interior sensor of the vehicle, the calibration being for the installation position inside of the vehicle of the vehicle interior sensor, the temporary reference device being a stand-alone device and comprising a reference feature detectable by the vehicle interior sensor, the temporary reference device being arranged to be installed by interfacing with a part of the vehicle interior to locate the temporary reference device, and thereby locate the reference feature at a known position within the interior of the vehicle.

15. A system comprising the temporarily installable reference device of claim 14 and a vehicle comprising the vehicle interior sensor and the part of the vehicle interior.15

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