Peli, Other thoughts.
The robot choreography only showed angular mapping where it was likely just matching the g vector. I did not see any plan view choreography. So a single accelerometer would work as all the angular response was orthogonal to g. This matches your thinking. The accelerometer is like a puddle of water that stays in the 'lowest' part of the phone. Also my thought was the 2 sensor location was more robust to the ways people might carry a phone than a 1 axis compass would be (if mounted normal to the circuit card), but there are still cases where rotation could be happening with no differential signal between the two accelerometers: one is when they are both on the axis of rotation. Three 25 cent sensors, or an alarm when g from one of 2 sensors aims at the other solves this. It certainly is more convenient to have a single sensor. The math is a lot easier. If the high level software acts on a compass signal, there must be way to get that function at an affordable price. On May 20, 3:28 pm, "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> wrote: > Peli, > > I must agree that bearing is the place to start. Two spaced > accelerometers can keep you from "losing your bearings." > > Yes, acceleration is indeed a vector quantity: dv/dt. And it can be > integrated to get velocity: dx/dt also vector. > > Yaw is a fancy word, I think, for angular acceleration, velocity, or > displacement. Two 3-axis sensors separated by some distance, r, will > experience different accelerations if there is rotation. > > If you calibrate with bearing frequently, and automatically, the > spaced accelerometers can send rotation information about (around) the > Gravity vector, which will be the same as a compass. For less than a > dollar. > > The question is: how fast will the accelerometers lose bearing? For > normal 'walk, scan' use this is well posed. > > There is some body on the web who choreographs a robot with a cell > phone. He may have a yaw sensor, but two spaced accelerometers would > work well enough. > > Thank you for the conversation. Please speak up if I left something > out. > > ed > > On May 20, 7:21 am, Peli <[EMAIL PROTECTED]> wrote: > > > > > I think it should be rather bearing and orientation sensors that you > > have to combine to simulate a compass: > > > The accelerometer can not indicate any direction except > > "down" (direction of gravity). Imagine the following thought > > experiment: Put a 3-axis accelerometer somewhere, and rotate it slowly > > around the z-axis (that points upwards). The accelerometer values will > > not indicate any change, since the direction for "down" relative to > > the device will always stay the same. > > > This will also not happen if you include 2 or more accelerometers into > > one device: Accelerometers can not keep direction. > > > What you need is an orientation sensor - made of gyroscopes. This > > could keep orientation information, but is larger and more expensive > > than accelerometer sensor. > > > Here is one example that combines accelerometer, orientation, and > > compass sensors:http://www.microstrain.com/3dm-gx2.aspx > > but this would be too expensive for phones. Probably, the compass > > sensor alone would be cheaper (but I'm just guessing here..), so that > > it could make more sense to simulate an orientation sensor using > > compass and accelerometer :-) > > > You can try it out in the OpenIntents Sensor simulator: > > "Yaw"ing will not change accelerometer values, but orientation and > > compass values.http://www.openintents.org/en/node/6 > > > Peli > > > On May 19, 7:13 pm, "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> wrote: > > > > Thanks. > > > > On May 19, 7:52 am, Alex Pisarev <[EMAIL PROTECTED]> wrote: > > > > > As far as I remember, OpenIntent's Sensor Simulator managed to emulate > > > > compass somehow, however, didn't look details. > > > > > Regards, > > > > Alex > > > > > On May 19, 3:33 pm, "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> wrote: > > > > > > Hi James, > > > > > > This is helpful. Thank you. It is good to know someone is thinking > > > > > about this. After reading the IEEE abstract, a little clarification on > > > > > use is always helpful. > > > > > > Our applications are eyes free, because the phone should not be > > > > > competing for those revenue generating resources. So use will happen > > > > > with the phone stored on the person’s body, say, in a shirt pocket, > > > > > held to the person's ear, or on their belt. The compass needs to work > > > > > no matter how the phone is oriented. The IEEE abstract seemed unclear > > > > > on how it would work in a handheld device. It would be great for cars, > > > > > though. With the two accelerometers, there is a calibration routine > > > > > where a person wears the phone normally and walks in one direction. 10 > > > > > ft should be enough to get enough calibration to be useful. It can > > > > > recalibrate in the background and alarm or adjust ... > > > > > > Sensor Fusion is a new word for me. Differential sensors of finite > > > > > resolution have been around for a long time. Consider the roach, or > > > > > any bug with antennae. They sample air at distant points allowing the > > > > > organism to select a direction. The longer the antennae, the smaller > > > > > the gradient the organism can detect with sensors of a fixed > > > > > resolution. Long antennae help folks figure out what is going on. > > > > > Sampling acceleration at distant points is going to give you better > > > > > information on angular velocity and acceleration (how fast you are > > > > > spinning) than using a single sensor in the same way. > > > > > > Thank you for pointing out that radio field interaction can provide > > > > > information... since a human body can influence that, it is probably > > > > > good to not rely on that method. Two sensors a fixed distance apart > > > > > should require little attention and provide good results across many > > > > > devices once it is engineered. > > > > > > My job is to show why it is worthwhile to spend that dollar for > > > > > pedestrians who don’t read maps. Android has the tools to do that, > > > > > even in today’s SDK. > > > > > > On May 18, 7:48 am, James <[EMAIL PROTECTED]> wrote: > > > > > > > A MEMS chip can be a collection of sensors (temperature, > > > > > > accelerometer > > > > > > (x,y,z), atmospheric pressure, Hall effect sensor (compass), ...) > > > > > > all > > > > > > built into the same chip. In mass production the chip could be > > > > > > relatively inexpensive. > > > > > > >http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/20/35967/017046.... > > > > > > > However, an Android shortcut would be to use the GPS sensor and your > > > > > > relative direction of travel to produce a compass bearing over 100 > > > > > > feet of uniform travel. For each model of cell phone the antenna > > > > > > sensitivity changes as you rotate the cell phone about a point. > > > > > > This > > > > > > could potentially be tied in with relative position movement to > > > > > > estimate a compass bearing about a point. > > > > > > > But as I said, the lookup table would be different for each model of > > > > > > cell phone. > > > > > > > This type of engineering where you take two sensors with low > > > > > > resolution to combine their results to provide greater resolution is > > > > > > called "Sensor Fusion". > > > > > > > Basically a cell phone antenna signal does NOT have the same signal > > > > > > profile when you rotate left versus rotate right. This can be > > > > > > capitalized upon to determine the relative bearing of which the > > > > > > compass is facing. Coupled with the cell phone GPS the relative > > > > > > bearing can be referenced to the true bearing. A lookup table can > > > > > > provide a correction factor and thereby produce Magnetic Bearing; > > > > > > vis > > > > > > vi Compass. > > > > > > > James Dunn > > > > > > Table of Contents - Similar Insights related to technology > > > > > > applicationshttp://blog.360.yahoo.com/jamesbdunn?p=207 > > > > > > > On May 15, 9:23 pm, "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> wrote: > > > > > > > > I have no idea how much a cell phone with a compass costs. I > > > > > > > don't see > > > > > > > why it would be expensive if there were enough of a market to > > > > > > > micro > > > > > > > machine it like all those tiny mirrors. > Who knows these answers? > > > > > > > > Thanks, > > > > > > > Ed- Hide quoted text - > > > > > > > - Show quoted text -- Hide quoted text - > > > > > > - Show quoted text -- Hide quoted text - > > > > > - Show quoted text -- Hide quoted text - > > > - Show quoted text -- Hide quoted text - > > - Show quoted text - --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Android Discuss" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/android-discuss?hl=en -~----------~----~----~----~------~----~------~--~---
