Summary of the invention
The main purpose of the present invention is to provide a kind of UAV Flight Control method and devices, it is intended to automatically control nothingIt is man-machine to carry out surrounding flight towards target object, and shot, reduce human intervention.
To achieve the above object, the present invention provides a kind of UAV Flight Control method, this method comprises:
Obtain the characteristic information of target object；
It is determined according to the characteristic information of the target object around radius and around mode；
Shooting destination is determined according to the circular radius and around mode, and in unmanned plane during flying to determining shooting destinationWhen, it is shot.
Preferably, the characteristic information of the target object includes the location information and shape information of target object, wherein is obtainedThe step of taking the location information of the target object include:
Location information acquisition request is sent to target object, and receives the target object and obtains according to the positional informationRequest the location information returned；Or
The unmanned plane during flying is controlled to the surface of target object, obtains the difference in height of the unmanned plane and target objectAnd the current location information of the unmanned plane is obtained, and according to the current location information determination of the difference in height and unmanned planeThe location information of target object；Or
The location information of target object is obtained in the controlling terminal with map function with the UAV Communication.
Preferably, it is determined according to the characteristic information of the target object and includes: around the step of radius
Location information of the unmanned plane when opening around mode is obtained, and is being opened according to the unmanned plane around mouldThe location information of location information and the target object when formula is determined around radius；Or
According to the volume size of the target object and the image or video quality of selection, in preset mapping relationsIn, find corresponding circular radius.
Preferably, it is determined according to the characteristic information of the target object and includes: around the step of mode
The height value of the target object is obtained, and obtains target object in the perspective plane product value of horizontal plane；
Determine that, around mode, the circular mode includes with half according to the height value of the target object and perspective plane product valueThe contour circular mode of diameter, the contour circular mode of different radii surround mode with radial spi.
Preferably, shooting destination is determined described according to the circular radius and around mode, and arrive in unmanned plane during flyingWhen determining shooting destination, after carrying out shooting step further include:
The 3D information of target object is determined according to captured picture or video data；
3D printer is sent by the 3D information；
The 3D printer is printed after receiving the 3D information, to obtain the 3D model of target object.
In addition, to achieve the above object, the present invention also provides a kind of UAV Flight Control device, which includes:
Module is obtained, for obtaining the characteristic information of target object；
First determining module, for being determined according to the characteristic information of the target object around radius and around mode；
Control module module for determining shooting destination according to the circular radius and around mode, and flies in unmanned planeWhen row arrives determining shooting destination, shot.
Preferably, the characteristic information of the target object includes the location information and shape information of target object, described to obtainModulus block is also used to send location information acquisition request to target object, and receives the target object and believed according to the positionCease the location information that acquisition request returns；Or for controlling the unmanned plane during flying to the surface of target object, described in acquisitionThe current location information of the difference in height and the acquisition unmanned plane of unmanned plane and target object, and according to the difference in height and nobodyThe current location information of machine determines the location information of the target object；Or for the UAV Communication have mapThe location information of target object is obtained in the controlling terminal of function.
Preferably, first determining module includes radius determination unit, is surround for obtaining the unmanned plane in unlatchingLocation information when mode, and the position of the location information and the target object according to the unmanned plane when opening around modeConfidence breath, determines around radius；Or for according to the volume size of the target object and the image or video quality of selection,In preset mapping relations, corresponding circular radius is found.
Preferably, first determining module further includes surrounding pattern determining unit, for obtaining the target objectHeight value, and target object is obtained in the perspective plane product value of horizontal plane, and according to the height value of the target object and perspective planeProduct value determines that around mode, the circular mode includes the contour circular mode of same radius, the contour circular mode of different radii, with halfDiameter spiral surrounding mode.
Preferably, described device further include:
Second determining module, for the picture of shooting or video data to be determined to the 3D information of target object；
Sending module, for the 3D information to be sent to 3D printer；
3D printer, for being printed after receiving the 3D information, to obtain the 3D model of target object.
UAV Flight Control method and device of the invention, this method comprises: obtaining the characteristic information of target object；RootIt determines according to the characteristic information of the target object around radius and around mode；It is determined according to the circular radius and around modeDestination is shot, and in shooting destination of the unmanned plane during flying to determination, is shot；Unmanned plane can automatically be controlled towards targetObject carries out surrounding flight, and is shot, and human intervention is reduced.
Specific embodiment
It should be appreciated that the specific embodiments described herein are merely illustrative of the present invention, it is not intended to limit the present invention.
Referring to Fig.1, Fig. 1 is the flow diagram of the first embodiment of UAV Flight Control method of the present invention, this methodInclude:
S10, the characteristic information for obtaining target object.
In one embodiment, the characteristic information of the target object includes the location information and shape information of target object, alsoThe step of may include the volume size of target object, that is, obtaining the characteristic information of target object are as follows: obtain the position of target objectInformation and shape information can also obtain the volume size of target object.The location information longitude and latitude and height of the target objectIt indicates, the height of the target object refers to the height of the target object with respect to the horizontal plane.
Optionally, the location information of target object can be obtained in the following manner: being sent location information to target object and obtainedRequest is taken, and receives the location information that the target object is returned according to the location information acquisition request.It is placed in target objectPosition detecting module, such as GPS module, target object measure the longitude and latitude and height of the target object, the target by GPS moduleFor object when receiving location information acquisition request, the longitude and latitude and height that measurement is read from the GPS module return to the transmissionThe request end of information acquisition request.
Optionally, the location information of target object can be obtained in the following manner: control unmanned plane during flying to target objectSurface, obtain the difference in height of the unmanned plane and target object and obtain the current location information of the unmanned plane, and according to thisDifference in height and the current location information of unmanned plane determine the location information of the target object.Unmanned plane during flying is controlled to target objectSurface image recognition is carried out to the image of shooting, so specifically, can shoot by the unmanned plane to target objectDetermine the center of the target object afterwards, then control the aircraft flight to the center of target object top, namelyAircraft flight is controlled to the surface of target object.At the surface of unmanned plane during flying to target object, by this nobodyHeight sensor (such as ultrasonic sensor) on machine measures the difference in height between the unmanned plane and target object, while passing through nothingPosition detecting module on man-machine, such as GPS module measure the longitude and latitude of the unmanned plane by the GPS module built in the unmanned planeAnd height, the longitude and latitude of the unmanned plane are the longitude and latitude of target object, the height of the height of the unmanned plane and unmanned plane measurementThe difference of degree difference is the height of target object.
Optionally, the location information of target object can be obtained in the following manner: with the UAV Communication have groundThe location information of target object is obtained in the controlling terminal of figure function.Specifically, there is map to what is connect with UAV CommunicationControlling terminal (such as mobile phone, tablet computer or ground control station terminal) send target object position information acquisition request, andReceive the location information that the controlling terminal is returned according to the target object information acquisition request.The controlling terminal is receiving targetAfter object location information acquisition request, target object is determined in controlling terminal, knows target from the map of the controlling terminalThe longitude and latitude of target object and height are returned to and send target object position letter by the longitude and latitude and height of object, the controlling terminalCease the request end of acquisition request.
S20, it is determined according to the characteristic information of the target object around radius and around mode.
In this step, it is determined according to the characteristic information of target object around radius and around mode, to the target pairAs taking suitable image or video.
Optionally, the step of which determines around radius are as follows: obtain the unmanned plane and existLocation information when opening around mode, and location information and the target object according to the unmanned plane when opening around modeLocation information, determine around radius.Location information of the unmanned plane when opening around mode can be by built in the unmanned planePosition detecting module obtain, the location information coordinate points A (X when opening around mode of the unmanned planep, Yp, Zp) tableShow, the location information coordinate points B (X of the target objectt, Yt, Zt) indicate, it can be calculated by the following formula around radius RIt arrives:
Optionally, the step of which determines around radius are as follows: according to the target objectVolume size and selection image or video quality, preset volume size and the image or video quality of selection withIn the mapping relations of radius, determine around radius.Preset volume size and image or video quality and around halfThe mapping relations of diameter, as shown in Table 1.According to the volume size of the target object and the image or video quality of selection, at thisVolume size and image or video quality find corresponding circular radius in the mapping relations of radius；Specifically,It first determines volume range belonging to the volume size of the target object, then finds volume range belonging to this and selectionImage or the corresponding circular radius of video quality, the as corresponding circular radius of the target object, such as the volume of the target objectVolume range belonging to size v is [V2, V3), the image or video quality selected is q2, then from the volume size and image orVideo quality is R with that in the mapping relations of radius, can find circular radius2。
Table one:
| Volume size V | Image or video quality | Around radius R |
| [V1, V2) | q1 | r1 |
| [V2, V3) | q2 | r2 |
| [V3, V4) | q3 | r3 |
| …… | | …… |
The shape information of the target object include target object height value and target object horizontal plane projected areaValue.The height value of the target object refers to target object upper surface to the shortest distance of lower surface.
The target object is when the perspective plane product value of horizontal plane is that the target object is just put, in the projected area of horizontal planeValue.
Optionally, the step of being determined according to the characteristic information of the target object around mode are as follows: obtain the height of target objectAngle value, and target object is obtained in the perspective plane product value of horizontal plane；According to the height value of the target object and perspective plane product valueDetermine that the circular mode includes the contour circular mode of same radius, the contour circular mode of different radii, same radial spi around modeAround mode.Specifically, according to the target object horizontal plane perspective plane product value and height value square relationship determine ringAround mode, the unit of the perspective plane product value and height value square unit it is identical；If specifically, the following steps are included: S21,The perspective plane product value of the target object is greater than or equal to square of the height value, and the perspective plane product value of the target object and the heightAngle value square difference be less than or equal to the first difference threshold, it is determined that around mode be with the contour circular mode of radius；If the perspective plane product value of S22, the target object is greater than or equal to square of the height value, and the perspective plane product value of the target objectWith the height value square difference be greater than the first difference threshold, it is determined that around mode be the contour circular mould of different radiiFormula；If the perspective plane product value of S23, the target object is less than square of the height value, and square of the height value of the target objectIt is less than or equal to the first difference threshold with the difference of the perspective plane product value, it is determined that around mode for the contour circular mould of radiusFormula；If the perspective plane product value of S24, the target object is less than square of the height value, and square of the height value of the target objectIt is greater than the first difference threshold with the difference for projecting the area value, it is determined that the mode that surround is with radial spi around mode.
First difference threshold can be set as needed.If the perspective plane product value of the target object is greater than or equal to the heightSquare of value, and the perspective plane product value of the target object and the height value square difference be less than or equal to the first difference valveValue, then it is assumed that the perspective plane product value of the target object is suitable with height value, can use to the target object contour circular with radiusMode.
If the perspective plane product value of the target object is greater than or equal to square of the height value, and the perspective plane of the target objectProduct value and the height value square difference be greater than the first difference threshold, then it is assumed that the target object, can be to the mesh in flatIt marks object and uses the contour circular mode of different radii.
If the perspective plane product value of the target object is less than square of the height value, and square of the height value of the target objectIt is less than or equal to the first difference threshold with the difference of the perspective plane product value, then it is assumed that the perspective plane product value and height of the target objectValue quite, can use with radius contour circular mode the target object.
If the perspective plane product value of the target object is less than square of the height value, and square of the height value of the target objectIt is greater than the first difference threshold with the difference of the perspective plane product value, then it is assumed that the target object is in strip column, can be to the target pairAs surrounding mode using radial spi.
S30, shooting destination is determined according to the circular radius and around mode, and navigate in unmanned plane during flying to determining shootingWhen point, shot.
In this step, the shooting destination determined includes the number for shooting destination and the coordinate information of each shooting destination.
In one embodiment, when the circular mode is circular mode contour with radius, shooting is calculated in the following mannerThe number of destination and the coordinate information of shooting destination, calculate minimum angles θ, θ=2* according to the detour radius R of above-mentioned determinationArcsin (l/2R) determines shooting destination number N further according to the θ, and number N, which is calculated by the following formula, to be obtained:
The coordinate of each shooting destination is (Xt+ R*cos (2 π/N*n), Yt+ R*sin (2 π/N*n), Zt), wherein n=0,1,2 ..., N-1,2 π/N indicate unit radian.
In one embodiment, it in the circular mode circular mode contour for different radii, calculates clap in the following mannerThe number of destination and the coordinate information of shooting destination are taken the photograph, is determined according to preset rules need circular circle number i, two adjacent rings firstInterval g, the radius R respectively enclosedj=R+ (j-1) * g, j=1,2 ..., i；Further according to the detour radius R of above-mentioned determinationjIt calculates eachThe minimum angles θ of circlej, θj=2*arcsin (l/2Rj), further according to the θjDetermine the shooting destination number N of each circlej, number NjIt is logicalFollowing formula is crossed to be calculated:
Total shooting destination number N are as follows:The coordinate of each shooting destination respectively enclosed is ((Xt+Rj*cos(2π/Nj* n), Yt+Rj*sin(2π/Nj* n), Zt)), wherein n=0,1,2 ..., Nj- 1,2 π/NjIndicate unit radian.
In one embodiment, when the circular mode is to surround mode with radial spi, shooting is calculated in the following mannerThe number of destination and the coordinate information of shooting destination, need circular circle number i according to preset rules determination, two adjacent ringsIt is spaced h；Minimum angles θ, θ=2*arcsin (l/2R) are calculated according to the detour radius R of above-mentioned determination, is determined further according to the θ everyThe shooting destination number N of one circle0, number N0It is calculated by the following formula and obtains:
Total shooting destination number N are as follows: N=i*N0.The coordinate of each shooting destination respectively enclosed is (Xt+R*cos(2π/N0*N), Yt+R*sin(2π/N0* n), Zt+ (j-1) * h), wherein n=0,1,2 ..., N0- 1,2 π/N0Expression unit radian, j=1,2……、i。
Using above-described embodiment, by the characteristic information for obtaining target object；It is true according to the characteristic information of the target objectSurely around radius and around mode；Shooting destination is determined according to the circular radius and around mode, and in unmanned plane during flying to reallyWhen fixed shooting destination, shot；Unmanned plane can automatically be controlled to carry out surrounding flight towards target object, and clappedIt takes the photograph, reduces human intervention.
It is the flow diagram of the second embodiment of UAV Flight Control method of the present invention referring to Fig. 2, Fig. 2.
Based on the second embodiment of above-mentioned UAV Flight Control method, after step S30, this method further include:
S40, the 3D information that target object is determined according to captured picture or video data.
The picture or video data of the shooting are analyzed, the 3D information of the target object is obtained.
S50,3D printer is sent by the 3D information.
The 3D information can be sent to 3D printer by wired or wireless way, can such as be incited somebody to action by 2.4G, 5.8G, wifi3D information is sent to 3D printer.
S60, the 3D printer are printed after receiving the 3D information, to obtain the 3D model of target object.
It is the structural schematic diagram of the first embodiment of UAV Flight Control device of the present invention, the device referring to Fig. 3, Fig. 3Include:
Module 10 is obtained, for obtaining the characteristic information of target object；
First determining module 20, for being determined according to the characteristic information of the target object around radius and around mode；
Control module 30, for determining shooting destination according to around radius and around mode, and in unmanned plane during flying to reallyWhen fixed shooting destination, shot.
In one embodiment, the characteristic information of the target object includes the location information and shape information of target object, alsoIt may include the volume size of target object, i.e., the acquisition module 10 is also used to obtain the location information of target object and shape is believedBreath.The location information longitude and latitude and height of the target object indicate that the height of the target object refers to that the target object is oppositeIn the height of horizontal plane.
Optionally, which can obtain the location information of target object in the following manner: send out to target objectLocation information acquisition request is sent, and receives the location information that the target object is returned according to the location information acquisition request.TargetPosition detecting module, such as GPS module are built-in in object, target object measures the target object by built-in GPS moduleLongitude and latitude and height, the target object read the longitude and latitude of measurement when receiving location information acquisition request from the GPS moduleDegree and height return to the request end of the transmission information acquisition request.
Optionally, which can obtain the location information of target object in the following manner: control unmanned plane fliesRow arrives the surface of target object, obtains the difference in height of the unmanned plane and target object and obtains the current position letter of the unmanned planeIt ceases, and determines the location information of the target object according to the current location information of the difference in height and unmanned plane.Unmanned plane is controlled to flyRow arrives the surface of target object, specifically, can be shot by the unmanned plane to target object, carries out to the image of shootingImage recognition, then determines the center of the target object, then controls the aircraft flight to the center of target objectTop, namely control aircraft flight is to the surface of target object.At the surface of unmanned plane during flying to target object,The difference in height between the unmanned plane and target object is measured by the height sensor (such as ultrasonic sensor) on the unmanned plane,Simultaneously by the position detecting module on unmanned plane, such as GPS module, measure this nobody by the GPS module built in the unmanned planeThe longitude and latitude and height of machine, the longitude and latitude of the unmanned plane are the longitude and latitude of target object, the height of the unmanned plane and this nobodyThe difference of the difference in height of machine measurement is the height of target object.
Optionally, which can also obtain the location information of target object in the following manner: with this nobodyThe location information of target object is obtained in the controlling terminal with map function of machine communication.Specifically, the acquisition module 10 toThe controlling terminal (such as mobile phone, tablet computer or ground control station terminal) with map connecting with UAV Communication sends meshObject location information acquisition request is marked, and receives the controlling terminal and is believed according to the position that the target object information acquisition request returnsBreath.The controlling terminal determines target object, from this after receiving target object position information acquisition request in controlling terminalKnow the longitude and latitude and height of target object on the map of controlling terminal, the controlling terminal is by the longitude and latitude and height of target objectReturn to the request end for sending target object position information acquisition request.
First determining module 20 is determined according to the characteristic information of target object around radius and around mode, to the meshMark object takes suitable image or video.
First determining module 20 includes radius determination unit, which is opening for obtaining the unmanned planeLocation information when around mode, and the position of the location information and the target object according to the unmanned plane when opening around modeConfidence breath, determines around radius；Or for according to the volume size of the target object and the image or video quality of selection,In preset mapping relations, corresponding circular radius is found.
Location information of the unmanned plane when opening around mode can be obtained by the position detecting module built in the unmanned plane, location information coordinate points A (X of the unmanned plane when opening around modep, Yp, Zp) indicate, the position of the target objectInformation coordinate points B (Xt, Yt, Zt) indicate, it can be calculated by the following formula to obtain around radius R:
The preset mapping relations are as follows: volume size and image or video quality and the mapping relations around radius, in advanceVolume size and image or video quality and the mapping relations around radius are first set, as shown in Table 1.According to the target pairThe volume size of elephant and the image or video quality of selection, in the volume size and image or video quality and around radiusMapping relations in, find corresponding circular radius；Specifically, first determining volume belonging to the volume size of the target objectThen range finds the image or the corresponding circular radius of video quality of the volume range belonging to this and selection, as shouldThe corresponding circular radius of target object, the volume range as belonging to the volume size v of the target object are [V2, V3), the figure of selectionPicture or video quality are q2, then can look into from the volume size and image or video quality in the mapping relations of radiusFinding around radius is R2。
The shape information of the target object include target object height value and target object horizontal plane projected areaValue.The height value of the target object refers to target object upper surface to the shortest distance of lower surface.
The target object is when the perspective plane product value of horizontal plane is that the target object is just put, in the projected area of horizontal planeValue.
In one embodiment, which further includes surrounding pattern determining unit, for obtaining the target pairThe height value of elephant, and obtain target object in the perspective plane product value of horizontal plane, and according to the area-altitude value of the target object andPerspective plane product value determines around mode, the circular mode include the contour circular mode of same radius, the contour circular mode of different radii,With radial spi around mode.
Specifically, the circular pattern determining unit according to the target object horizontal plane perspective plane product value and height valueSquare relationship determine around mode, the unit of the perspective plane product value and height value square unit it is identical；Specifically, if shouldThe perspective plane product value of target object is greater than or equal to square of the height value, and the perspective plane product value of the target object and the heightValue square difference be less than or equal to the first difference threshold, then the circular pattern determining unit determines that around mode be with halfThe contour circular mode of diameter；If the perspective plane product value of the target object is greater than or equal to square of the height value, and the target objectPerspective plane product value and the height value square difference be greater than the first difference threshold, then the circular pattern determining unit determinesIt is the contour circular mode of different radii around mode；If the perspective plane product value of the target object is less than square of the height value, andThe height value of the target object square is less than or equal to the first difference threshold with the difference of the perspective plane product value, then the circular mouldFormula determination unit determines that around mode be with the contour circular mode of radius；If the perspective plane product value of the target object is less than the heightValue square, and the height value of the target object square with project the area value difference be greater than the first difference threshold, then thisDetermine that around mode be with radial spi around mode around pattern determining unit.
First difference threshold can be set as needed.If the perspective plane product value of the target object is greater than or equal to the heightSquare of value, and the perspective plane product value of the target object and the height value square difference be less than or equal to the first difference valveValue, then it is assumed that the perspective plane product value of the target object is suitable with height value, which can determine to the targetObject is used with the contour circular mode of radius.
If the perspective plane product value of the target object is greater than or equal to square of the height value, and the perspective plane of the target objectProduct value and the height value square difference be greater than the first difference threshold, then it is assumed that the target object is in flat, the circular mouldFormula determination unit can determine to the target object using the contour circular mode of different radii.
If the perspective plane product value of the target object is less than square of the height value, and square of the height value of the target objectIt is less than or equal to the first difference threshold with the difference of the perspective plane product value, then it is assumed that the perspective plane product value and height of the target objectQuite, which can determine uses with radius contour circular mode the target object to value.
If the perspective plane product value of the target object is less than square of the height value, and square of the height value of the target objectIt is greater than the first difference threshold with the difference of the perspective plane product value, then it is assumed that the target object is in strip column, and the circular mode is trueOrder member can determine to the target object using radial spi around mode.
The shooting destination that the control module 30 determines includes the number for shooting destination and the coordinate information of each shooting destination.
In one embodiment, when the circular mode is circular mode contour with radius, which passes through followingMode calculates the number of shooting destination and the coordinate information of shooting destination, calculates minimum angle according to the detour radius R of above-mentioned determinationθ, θ=2*arcsin (l/2R) are spent, determines shooting destination number N further according to the θ, number N, which is calculated by the following formula, to be obtained:
The coordinate of each shooting destination is (Xt+ R*cos (2 π/N*n), Yt+ R*sin (2 π/N*n), Zt), wherein n=0,1,2 ..., N-1,2 π/N indicate unit radian.
In one embodiment, when the circular mode is the contour circular mode of different radii, the control module 30 by withUnder type calculates the number of shooting destination and the coordinate information of shooting destination, is determined according to preset rules need to surround firstCircle number i, the interval g of two adjacent rings, the radius R respectively enclosedj=R+ (j-1) * g, j=1,2 ..., i；Further according to above-mentioned determinationDetour radius RjCalculate the minimum angles θ of each circlej, θj=2*arcsin (l/2Rj), further according to the θjDetermine the shooting destination of each circleNumber Nj, number NjIt is calculated by the following formula and obtains:
Total shooting destination number N are as follows:The coordinate of each shooting destination respectively enclosed is ((Xt+Rj*cos(2π/Nj* n), Yt+Rj*sin(2π/Nj* n), Zt)), wherein n=0,1,2 ..., Nj- 1,2 π/NjIndicate unit radian.
In one embodiment, when the circular mode is to surround mode with radial spi, which passes through followingMode calculates the number of shooting destination and the coordinate information of shooting destination, needs circular circle number according to preset rules determinationI, the interval h of two adjacent rings；Minimum angles θ, θ=2*arcsin (l/2R), then root are calculated according to the detour radius R of above-mentioned determinationThe shooting destination number N of each circle is determined according to the θ0, number N0It is calculated by the following formula and obtains:
Total shooting destination number N are as follows: N=i*N0.The coordinate of each shooting destination respectively enclosed is (Xt+R*cos(2π/N0*N), Yt+R*sin(2π/N0* n), Zt+ (j-1) * h), wherein n=0,1,2 ..., N0- 1,2 π/N0Expression unit radian, j=1,2……、i。
It is the structural schematic diagram of the second embodiment of UAV Flight Control device of the present invention referring to Fig. 4, Fig. 4.
Based on the first embodiment of above-mentioned UAV Flight Control device, the device further include:
Second determining module 40, for the picture of shooting or video data to be determined to the 3D information of target object；
Sending module 50, for the 3D information to be sent to 3D printer；
3D printer 60, for being printed after receiving the 3D information, to obtain the 3D model of target object.
Second determining module 40 analyzes the picture or video data of the shooting, obtains the 3D letter of the target objectBreath.
The 3D information can be sent to 3D printer by wired or wireless way by the sending module 50, can such as pass through wifi3D information is sent to 3D printer.
The above is only a preferred embodiment of the present invention, is not intended to limit the scope of the invention, all to utilize this hairEquivalent structure or equivalent flow shift made by bright specification and accompanying drawing content is applied directly or indirectly in other relevant skillsArt field, is included within the scope of the present invention.