DE102013214628A1 - Distance determining device, arrangement with the distance determining device, method and computer program - Google Patents

Abstract

Automatic fire detectors can detect a fire based on different measuring methods. For example, fire alarms are now known which can detect and report a fire via temperature measurement, smoke density measurement, etc. Due to the availability of cost-effective image sensors, it is now also known to operate automatic fire detectors with video cameras, wherein the fire is detected by a digital image processing. A distance determining device 1 with a video camera 2 for detecting a monitoring area U and for outputting a video sequence is proposed, wherein in the video sequence the monitoring area U is shown with an ascending smoke cloud 5 of a fire 6 and / or can be displayed, with an evaluation device 3 for evaluating the Video sequence, wherein the evaluation device 3 is a distance module 10 for determining a distance D of the cloud of smoke 5 from the video camera 2 on the basis of a speed determined by digital image processing rate vof the cloud of smoke 5 in camera coordinates of the video camera 2 and a predeterminable ascent speed vo in world coordinates.

Description

State of the art

The invention relates to a distance determining device having the features of the preamble of claim 1. The invention also relates to an arrangement with the distance determining device, a method for determining a distance and a corresponding computer program.

Automatic fire detectors can detect a fire based on different measuring methods. For example, fire alarms are now known which can detect and report a fire via temperature measurement, smoke density measurement, etc. Due to the availability of cost-effective image sensors, it is now also known to operate automatic fire detectors with video cameras, wherein the fire is detected by a digital image processing.

The publication DE 10 2008 001 383 A1 , which is probably the closest prior art, relates to a detection device for the detection of fires and / or fire characteristics, wherein as an image sensor sensor element, in particular a camera device is used.

Disclosure of the invention

In the context of the invention, a distance determination device having the features of claim 1, an arrangement with the distance determination device having the features of claim 9, a method having the features of claim 10 and a computer program having the features of claim 11 are proposed. Preferred or advantageous embodiments of the invention will become apparent from the dependent claims, the following description and the accompanying drawings.

Thus, according to the invention, a distance determining device is proposed, which has a video camera for detecting a monitoring area.

The video camera may e.g. be designed as a CCD camera or as a CMOS camera or in another type. It can be realized in particular as a black-and-white camera or as a color camera. The video camera is designed and / or arranged to detect a surveillance area with its camera field of view. The monitoring area can be, for example, rooms or room sections in a building or even free areas in an environment.

The video camera can output a video sequence, wherein the video sequence consists of a sequence of temporally in particular equidistantly successively recorded images. In the video sequence, the surveillance area is displayed and / or displayed with an ascending smoke cloud of a fire. It is possible in principle that the fire or the fire is itself displayed on the video sequence. However, it is sufficient if only the ascending smoke cloud of the fire is shown.

Under the cloud of smoke are to understand fire gases that pull up from the fire. The ascending cloud of smoke can in particular have the form of a specifically vertically oriented smoke flare or smoke column. The phenomenon of rising of the cloud of smoke is due in particular to the high temperatures of the combustion gases or smoke aerosols in the cloud of smoke compared to the environment. The rate of ascent of the cloud of smoke is primarily dependent on the temperature of the smoke and can be assumed to be of a similar magnitude for different, even different, large fire sources, with optically similar smoke developments. In particular, the smoke density in the cloud of smoke is so high that the cloud of smoke is visually recognizable. Particularly preferably, the cloud of smoke has contour features, such as e.g. Cumulus sections or smoke streaks, on.

Furthermore, the distance determination device comprises an evaluation device which is suitable and / or designed for the evaluation of the video sequence. Particularly preferably, the evaluation device is based on digital image processing. For example, the evaluation device can be designed as a digital data processing device, in particular as a computer.

According to the invention, it is proposed that the evaluation device has a distance module for determining a distance of the cloud of smoke from the video camera. Thus, the distance module allows a distance between the video camera and the cloud of smoke and thus to determine indirectly between the video camera and fire or fire.

The determination is carried out according to the invention on the basis of a rate of ascension of the cloud of smoke in camera coordinates of the video camera and a predeterminable ascent rate in world coordinates as determined by digital image processing.

The ascent speed of the cloud of smoke in camera coordinates is determined in particular with respect to the uncalibrated video camera. By contrast, the predeterminable ascent rate in world coordinates of a typical cloud of smoke is e.g. metrologically recorded or simply estimated. For example, it is easy to determine the speed with which a typical cloud of smoke rises in a normal fire. After there are different types of fire, the predeterminable ascent rate is in particular an averaged or adapted to the application ascent rate.

The advantage of the invention lies in the fact that the distance between the video camera and the cloud of smoke can be reliably estimated by comparing a measured ascent speed of the smoke cloud in camera coordinates and a predefinable ascent rate in world coordinates.

Normally, the problem with the distance estimation is that the cloud of smoke - unlike, for example, an object or a person - is not located at a bottom of the surveillance area, but floats freely in the surveillance area. Thus, conventional methods for determining the distance to an object can not be applied, for example, which presuppose that the foot point of an object in the surveillance area is on a floor surface. Rather, it is not possible to distinguish whether a cloud of smoke is very small and occurs at a small distance, or whether the cloud of smoke is very large and is located at a great distance.

By comparing the measured ascent rate in camera coordinates and the predeterminable ascent rate in world coordinates, a distance of the cloud of smoke from the video camera can be estimated by e.g. a ratio, in particular a quotient of the two ascent rates is used as a distance-dependent proportional value. With this model consideration, it is possible to easily determine the distance of the cloud of smoke to the video camera and thus implicitly on the distance of the fire to the video camera. Alternatively or additionally, it is also possible to determine the size of the cloud of smoke. In particular, a maximum height of the cloud of smoke in a vertical orientation, a maximum width in a horizontal orientation and / or an area in projection, in particular in each case in world coordinates, can be determined. This information is useful in the case of fire fighting, for example, to be able to switch on and locally sprinkler systems, or to be able to plan evacuations.

In a preferred implementation of the invention, the evaluation device has a flow module for determining the speed of the optical flow of the cloud of smoke in the video sequence, the speed of the optical flow being used as the rate of ascent of the cloud of smoke in camera coordinates. The optical flow in digital image processing and optical measurement technology is a calculated vector field that indicates the direction of movement and the speed of movement for pixels of an image sequence. The optical flow can be understood as the velocity vectors projected onto the image plane of visible objects, in the present case portions of the cloud of smoke. After the smoke cloud as a whole moves from bottom to top, a vector field results for the cloud of smoke, in which the vectors are at least rectified. On the basis of the vectors, the ascent rate can be determined in a simple manner, for example as maximum velocity or average velocity of the vectors of the vector field of the cloud of smoke. It is also possible that only vectors of the vector field are used whose base point are arranged in the center of the cloud of smoke. In particular, the optical flux is determined by the Horn-Schunck method.

In a preferred embodiment of the invention, the distance module is designed to use at least one camera parameter, in particular at least one constant camera parameter for determining the distance of the cloud of smoke from the video camera. In a preferred embodiment of the invention, the at least one camera parameter is dependent on intrinsic parameters of the video camera, such as the focal length, the opening angle, etc., and extrinsic parameters of the video camera in the surrounding area, in particular pitch angle relative to a ground surface, etc. By the at least one Camera parameters can be a simple conversion of metrologically detected ascent rate of the smoke cloud in camera coordinates to the distance of the cloud of smoke from the video camera, as will be explained below. The at least one camera parameter can be determined experimentally on the one hand. For example, it is possible to determine the at least one camera parameter to drop an object at a known distance from the video camera and to adjust the camera parameters based on known equations of motion so that the measured falling speed, an estimated falling speed of the object and the distance are consistent. Alternatively, it is also possible to calculate the at least one camera parameter if the intrinsic and extrinsic parameters are known.

In this connection, reference should be made in particular to the pitch angle of the camera, that is to say to the angle which relates to the angle of the main observation direction of the video camera relative to a horizontal ground. If the pitch angle is 0 degrees, the video camera detects the cloud of smoke sideways, with the cloud of smoke moving in a direction orthogonal to the main viewing direction of the video camera and the measured ascent rate directly related to the actual ascent rate. However, if the pitch angle is not equal to 0 degrees, for example 45 degrees, then only the projection of the object movement of the cloud of smoke in the image plane perpendicular to the main observation direction of the video camera is measured in the ascent rate measurement. Depending on the pitch angle, the at least one camera parameter must therefore be corrected.

In one possible embodiment of the invention, the measured ascent rate vof in the unit of pixels per second, the predefinable ascent rate vo in units of meters per second and the at least one camera parameter p in the unit pixels are indicated. The distance is then calculated in simple form according to the formula d = (Vo / Vof) × p. This embodiment shows that the distance determination - after calculation of the optical flow - can be performed very easily.

In a preferred embodiment of the invention, the evaluation device has an expansion module, which is designed to determine the extent of the cloud of smoke. The determination of the extent of the cloud of smoke, ie in particular a width of the cloud of smoke and a height of the cloud of smoke or an area of the cloud of smoke, can be calculated in a simple manner after determining the distance. It is thus possible, for example, to detect the cloud of smoke as a moving object by means of conventional techniques of digital image processing, such as object detection by subtracting a current video image of the video sequence from a static scene reference image and a subsequent segmentation. In a simple way, the extent in camera coordinates, so for example in pixels as a unit, can be determined and converted over the now known distance between the cloud of smoke and video camera in an expansion in world coordinates.

In a particularly preferred embodiment of the invention, the distance determining device only a single video camera for distance determination, so that the distance determination device is designed as a single-camera system.

It is further preferred that the distance determining device comprises a fire detection device, wherein a fire or the existence of the cloud of smoke is detected by digital image processing and is detected by means of digital image processing. Optionally, in addition to the fire detection device is designed to perform a plausibility check, wherein the distance and / or the size of the cloud of smoke are used as parameters to an actual fire of a controlled smoke area, such. from a cigarette, to distinguish. For example, a fire is classified as plausible only if the size has exceeded a certain, predefinable limit value and / or the distance is within a predefinable distance range. In particular, the distance determining device is designed as a fire alarm device. Another object of the invention relates to an arrangement with a distance determining device according to one of the preceding claims and with a monitoring area, wherein the distance determining device is arranged in the monitoring area.

A next aspect of the invention relates to a method for determining a distance between a video camera and a cloud of smoke, preferably with a distance determining device according to one of the preceding claims or with the arrangement as described above. In the method, a rate of ascension of the cloud of smoke is detected from a video sequence of the video camera and a distance between the cloud of smoke and the video camera is determined on the basis of the detected ascent speed of the smoke cloud in camera coordinates of the video camera and a predeterminable ascent rate in world coordinates. In particular, the distance determination device for carrying out the method is designed program-technically and / or circuit-wise.

Another object of the invention relates to a computer program with program code means having the features of claim 11.

Further features, advantages and effects of the invention will become apparent from the following description of a preferred embodiment of the invention and the accompanying figures. Showing:

1 a block diagram of a distance determining device as a first embodiment of the invention;

2 a schematic illustration of an application situation for explaining the method according to the invention;

3 in the same representation as in 2 another application situation.

The 1 shows a schematic representation of a distance determining device 1 which is formed in this embodiment as a fire detector for detecting a fire. The distance determining device 1 includes a video camera 2 whose field of view is directed to a monitoring area U. The video camera 2 has a main observation direction B. The main observation direction B forms in particular the optical axis of the video camera 2 ,

Furthermore, the distance determining device 1 an evaluation device 3 and a fire detection device 4 on.

In operation is the video camera 2 directed into the surrounding area U, so that the surveillance area U of the video camera 2 is detected. The video camera 2 generates a video sequence which is sent to the evaluation device 3 and the fire detection device 4 is forwarded. The fire detection device 4 is designed to recognize a fire in the surveillance area by analyzing the video sequence based on digital image processing and to report it as an option.

The evaluation device 3 On the other hand, it is designed to have a distance D between the video camera 2 and a cloud of smoke 5 a fire 6 in the monitoring area U to determine.

The determination of the distance D is difficult because the distance determining device 1 is designed as a single-camera device and for the monitoring area U only a video camera 2 provides. Upon detection of the monitoring area U, however, only a 2D image of the three-dimensional monitoring area U is detected, so that distance information is lost. Although it is possible with known image processing techniques, a video camera 2 or the video camera 2 To calibrate recorded video sequences such that distances can be derived. But additional assumptions are made or needed, so that, for example, the object to which the distance is to be determined, gets up on the floor. This situation is in the case of the cloud of smoke 5 not necessarily given, as the fire 6 not necessarily on the floor must be arranged. In particular, it is also possible that the fire 6 out of the field of view of the video camera 2 is arranged so that the video sequence only the cloud of smoke 5 shows.

Nevertheless, in order to be able to determine the distance D, in the distance determining device according to the invention 1 another method chosen, which is presented below as an embodiment of the invention.

In the 2 the measurement situation is roughly shown, with the video camera on the left side 2 and on the right side the cloud of smoke 5 and the fire 6 which is shown here by way of example on a horizontal ground 7 are arranged. When pictured by the video camera 2 For example, an object O in an object plane E is imaged onto an object O 'on an image plane G'. In the same way, however, an object movement in the plane G is imaged in an object movement in the image plane G '.

From other technical fields in the digital image processing, the determination of characteristics of the optical flow (optical flow) is known, as this is implemented for example by means of the Horn-Schunck method. In the optical flow method, the direction and speed of movements of image sections, which in some cases can be assigned to objects or object sections, are captured in video sequences. Here, a vector with a. For each image section Movement direction and a movement speed is determined, so that a vector field is formed with vectors that describe the direction of movement and the speed of movement of the respective image portion. In the same way, the optical flow of the cloud of smoke is now 5 certainly. The optical flow is determined on the image plane G 'and thus detected in camera coordinates. For example, the speed of movement of the optical flow is evaluated in units of pixels per second.

The determination of the optical flow is in a flow module 9 ( 1 ) and the speed of movement of the optical flow to a distance module 10 in the evaluation device 3 forwarded. From the moving speed of the optical flow, in particular from the above-described vector field of the optical flow, an ascent speed of the cloud of smoke becomes 5 in camera coordinates of the video camera 2 derived. This can be implemented, for example, by the movement velocities of all vectors of the vector field of image sections of the cloud of smoke 5 be averaged. Alternatively, other statistical methods may be used to derive the ascent rate, such as the use of median values, maximum value, etc. The ascent rate vof is optionally in the flow module 9 or in a subsequent distance module 10 carried out.

The distance module 10 Furthermore, a rate of ascent of the cloud of smoke in world coordinates, ie in particular in units of meters per second, as well as a constant camera parameter p are supplied. The constant camera parameter takes into account, on the one hand, the focal length and the opening angle of the video camera as intrinsic parameters 2 and as extrinsic parameters, for example, the pitch angle, ie the angle between the main observation direction B and the ground 7 , The ascent rate vo in world coordinates can be determined experimentally or as part of an initialization of the distance device 1 be adjusted.

The evaluation device 3 , in particular the distance module 10 is trained based on the formula: D = (vof / vo) · p calculate the distance D.

Thus, in the distance determining apparatus 1 exploited that a 3D object movement speed of the cloud of smoke 5 in the main observation direction B orthogonal object plane G is known.

However, it is not only possible to use the distance determining device 1 to use in the arrangement shown, but also, if the pitch angle, so the intermediate angle between the main observation direction B and ground 7 is not equal to 0. This measurement situation is in the 3 wherein it can be seen that the optical flow is still imaged onto the image plane G '. In the illustration shown, the camera parameter p has to be adapted to the extrinsic parameters, in this case the pitch angle.

Optionally, the distance determining device 1 an expansion module 12 on, which, knowing the distance D, the extent of the cloud of smoke 5 determined so that in addition to the distance D and the expansion of the cloud of smoke 5 from the distance determining device 1 can be issued. Optionally, a direction information can be output, which indicates the direction of the cloud of smoke 5 in relation to the position of the video camera 2 describes. The output of said data or parts thereof can be done via an interface, not shown, for example, to a security center.

In an exemplary calculation, the following values result: vo = 0.5 m / s; (typical smoke ascent rate) vof = 50 pixels / s; (derived from the optical flow) p = 1.3 x 10 ^ 3 pixels (exemplary camera parameter) D = (vof / vo) · p = 13m

The distance D between the video camera 2 and the cloud of smoke 5 becomes apparent in this example calculation 13 m determined.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102008001383 A1 [0003]

Claims (11)

Distance determining device ( 1 ) with a video camera ( 2 ) for detecting a monitoring area (U) and for outputting a video sequence, wherein in the video sequence the monitoring area (U) with a rising cloud of smoke ( 5 ) of a brand ( 6 ) and / or can be displayed, with an evaluation device ( 3 ) for evaluating the video sequence, characterized in that the evaluation device ( 3 ) a distance module ( 10 ) for determining a distance (D) of the cloud of smoke ( 5 ) from the video camera ( 2 ) based on a rate of ascension (vof) of the cloud of smoke determined by digital image processing ( 5 ) in camera coordinates of the video camera ( 2 ) and of a predeterminable ascent rate (vo) in world coordinates. Distance determining device ( 1 ) according to claim 1, characterized in that the evaluation device ( 3 ) a flow module ( 9 ) for determining the speed of optical flow of the cloud of smoke ( 5 ) in the video sequence as the ascent rate (vof) in camera coordinates. Distance determining device ( 1 ) according to one of the preceding claims, characterized in that the distance module ( 10 ) at least one camera parameter (p) for determining the distance (D) of the cloud of smoke ( 5 ) from the video camera ( 2 ) used Distance determining device ( 1 ) according to claim 3, characterized in that the at least one camera parameter (p) intrinsic parameters of the video camera ( 2 ) and extrinsic parameters of the surrounding area (U). Distance determining device ( 1 ) according to one of the preceding claims 3 or 4, characterized in that the rate of ascent (vof) of the cloud of smoke (vof) 5 ) in camera coordinates in the unit of pixels / time unit, the ascent rate (vo) in world coordinates in the unit meter / time unit and the at least one constant camera parameter (p) in the unit pixels is described, wherein the distance according to the formula D = (vof / vo) · p. Distance determining device ( 1 ) according to one of the preceding claims, characterized in that the evaluation device ( 3 ) an expansion module ( 12 ) for determining the extent of the cloud of smoke ( 5 ) having. Distance determining device ( 1 ) according to one of the preceding claims, characterized in that only a single video camera ( 2 ) is used for distance determination. Distance determining device ( 1 ) according to any one of the preceding claims, characterized in that the distance determining device ( 1 ) a fire detection device ( 4 ) having. Arrangement with the distance determining device ( 1 ) according to one of the preceding claims and the monitoring area (U), wherein the distance determining device ( 1 ) is arranged in the monitoring area (U). Method for determining a distance (D) between a video camera ( 2 ) and a cloud of smoke ( 5 ) in a monitoring area (U), preferably with the distance determining device ( 1 ) according to one of the preceding claims or with the arrangement according to claim 9, wherein from a video sequence of the video camera ( 2 ), wherein in the video sequence the monitoring area (U) with an ascending cloud of smoke ( 5 ) of a brand ( 6 ), a rate of ascent (vof) of the cloud of smoke ( 5 ) in camera coordinates of the video camera ( 2 ), the distance (D) being determined on the basis of the determined ascent rate (vof) and a predeterminable ascent rate (Vo). Computer program with program code means for carrying out all steps of the method according to claim 10, when the program is stored on a computer and / or on the distance determining device ( 1 ) is carried out by any one of claims 1 to 9.

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