kalman filter to improve the gps data received from an iPhone
in [DSP]
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From: Jerry Avins on 8 Jun 2010 09:40 On 6/8/2010 4:19 AM, claudegps wrote: > On 25 Mag, 16:28, "andreivig"<vig.andrei(a)n_o_s_p_a_m.gmail.com> > wrote: >> Hi, >> >> I am currently working on an navigation application for an iPhone device. >> The GPS data that I receive is not very accurate and I want to use a kalman >> filter. The problem is that I don't really know how to build the kalman >> equations for x and y coordinates. What kind of model should I use? > > Now iPhone4 has also the gyro! > 3 Axis accelerometer + 3 axis gyro and you have your IMU :) What is the drift rate? Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
From: Tim Wescott on 8 Jun 2010 09:48 On 06/08/2010 06:40 AM, Jerry Avins wrote: > On 6/8/2010 4:19 AM, claudegps wrote: >> On 25 Mag, 16:28, "andreivig"<vig.andrei(a)n_o_s_p_a_m.gmail.com> >> wrote: >>> Hi, >>> >>> I am currently working on an navigation application for an iPhone >>> device. >>> The GPS data that I receive is not very accurate and I want to use a >>> kalman >>> filter. The problem is that I don't really know how to build the kalman >>> equations for x and y coordinates. What kind of model should I use? >> >> Now iPhone4 has also the gyro! >> 3 Axis accelerometer + 3 axis gyro and you have your IMU :) > > What is the drift rate? No doubt it's high -- but at least with a gyro you have a chance! The pernicious thing about this GPS/Kalman application is that there is no threshold for how good the IMU must be unless you also specify the motion profile. If the motion is rich enough in accelerations (if, for instance, someone is holding the iPhone in their hand while walking) then the IMU doesn't have to be as good as it would if the assembly is bolted down to a car (where the IMU would have to be good enough to carry measurements while you're seeing accelerations no more severe than bumps in the road, or at least normal corners). -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
From: Tim Wescott on 8 Jun 2010 12:00 On 06/08/2010 06:48 AM, Tim Wescott wrote: > On 06/08/2010 06:40 AM, Jerry Avins wrote: >> On 6/8/2010 4:19 AM, claudegps wrote: >>> On 25 Mag, 16:28, "andreivig"<vig.andrei(a)n_o_s_p_a_m.gmail.com> >>> wrote: >>>> Hi, >>>> >>>> I am currently working on an navigation application for an iPhone >>>> device. >>>> The GPS data that I receive is not very accurate and I want to use a >>>> kalman >>>> filter. The problem is that I don't really know how to build the kalman >>>> equations for x and y coordinates. What kind of model should I use? >>> >>> Now iPhone4 has also the gyro! >>> 3 Axis accelerometer + 3 axis gyro and you have your IMU :) >> >> What is the drift rate? > > No doubt it's high -- but at least with a gyro you have a chance! > > The pernicious thing about this GPS/Kalman application is that there is > no threshold for how good the IMU must be unless you also specify the > motion profile. If the motion is rich enough in accelerations (if, for > instance, someone is holding the iPhone in their hand while walking) > then the IMU doesn't have to be as good as it would if the assembly is > bolted down to a car (where the IMU would have to be good enough to > carry measurements while you're seeing accelerations no more severe than > bumps in the road, or at least normal corners). > Note that your IMU would also have to be quite linear. I'm not sure that there's a path there, but it may be worth looking into. -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
From: claudegps on 8 Jun 2010 12:36 > > Now iPhone4 has also the gyro! > > 3 Axis accelerometer + 3 axis gyro and you have your IMU :) > > What is the drift rate? Difficult to say... but it's high... Try to look for Mems from ST and AD to find some info... (even if I'm not sure which on the IPhone uses...)
From: claudegps on 8 Jun 2010 12:40
On 8 Giu, 15:48, Tim Wescott <t...(a)seemywebsite.now> wrote: > On 06/08/2010 06:40 AM, Jerry Avins wrote: > > > > > On 6/8/2010 4:19 AM, claudegps wrote: > >> On 25 Mag, 16:28, "andreivig"<vig.andrei(a)n_o_s_p_a_m.gmail.com> > >> wrote: > >>> Hi, > > >>> I am currently working on an navigation application for an iPhone > >>> device. > >>> The GPS data that I receive is not very accurate and I want to use a > >>> kalman > >>> filter. The problem is that I don't really know how to build the kalman > >>> equations for x and y coordinates. What kind of model should I use? > > >> Now iPhone4 has also the gyro! > >> 3 Axis accelerometer + 3 axis gyro and you have your IMU :) > > > What is the drift rate? > > No doubt it's high -- but at least with a gyro you have a chance! > > The pernicious thing about this GPS/Kalman application is that there is > no threshold for how good the IMU must be unless you also specify the > motion profile. If the motion is rich enough in accelerations (if, for > instance, someone is holding the iPhone in their hand while walking) > then the IMU doesn't have to be as good as it would if the assembly is > bolted down to a car (where the IMU would have to be good enough to > carry measurements while you're seeing accelerations no more severe than > bumps in the road, or at least normal corners). Interesting. But shouldn't the car be an easier environment? In the car you have motion constrains (you can't turn fast, acceleration are always lees than 1g, ecc) and every movement can be easily related with GPS data. That should make calibration of the IMU much easier... isn't it? While walking, the user may turn around, move hands, rotate the device, put it into its pocket ecc... the user can do many many movement that can not be easily related to the GPS data. Moreover you can't fix any constrain in the motion model (or better: you really have lees constrains you can rely on) What I'm missing? Thanks |