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Dead reckoning or RF triangulation? Or something else?

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Resistanceisbutyl

Resistanceisbutyl

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Hello all. I am designing a system for research that requires the tracking, in real time, of objects (large rats) in a three-dimensional play field. I need fairly high accuracy, to within six inches at least, preferably more. My central system needs to know where each rat is at all times, so I will attach a small "man-pack" transmitter to each rat, for communication to a network of stationary transceivers.
My question is, what is the best method of tracking the rats within the field? I could be wrong, but I figure my only two choices are active triangulation, and dead reckoning. I have looked extensively, and have not found a suitable off-the-shelf solution. I figure I can bundle accelerometers together and average out the readings, to improve collective accuracy, and reduce noise. But I realize the reading will drift over time, and have to be re-zeroed during the exersize.
I figure the military has triangulation systems with enough accuracy to accomplish what I want, but for obvious reasons such a system may not be practical. I would appreciate any suggestions any of the members here have. Thanks
 
Thank you for the reply, I will look in to it. Unfortunately, one of the aspects of my project is the fact that the observation area is variable. I must make the nodes modular and mobile, so I can move them from area to area. I think I can limit the maximum distance from a man-pack to a node to no more than 25 feet.
 
What kind of sampling speed are you looking for? Based on the demo video on the link KJ6EAD supplied, that RFID solution didn't look like it had a very high sample rate (several seconds per scan is what it looked like, but I couldn't find any further detail so it's difficult to say for sure).

Have you thought about optical tracking - that is, set up multiple video cameras, perhaps at the upper corners pointing downward, tracking (3D triangulation) retroreflective dots on the rats? The only problem with this scheme is not being able to identify each individual rat. Perhaps active IR dots, sending out a pulse code which could be decoded as part of the video stream? Another method might be to have addressable active IR dots, tracked by the cameras, each lighted in-turn via an RF link. Occlusion of the dots (whether passive or active) could be an issue, but with enough cameras to provide overlap, and proper design of the testing area (ie - no tunnels or tubes allowed, for instance), most problems could be overcome.

Another possibility might be a magnetic system - the rats pack would house a small coil (consisting of three orthogonal coils) that could be pulsed via addressable RF means, like the active IR dots above, and pickup coils on the walls and ceiling would determine X/Y/Z position based on magnetic strength (at issue here would be the battery life of the man-packs, plus the noisiness inherent in the system that would need to be filtered out, plus the need to build a non-ferrous environment, among other problems).

If you needed heading or other orientation data, then an RF link back from the man-pack from an on-board IMU might work well with the above ideas. A great issue to overcome, no matter what system, would be battery life for the man-packs (but may lithium ion batteries would help there).

I don't think, though, that you're going to find much off-the-shelf hardware for this kind of tracking (with the exception of an all-optical system - those are sold, though mostly as a passive system - for motion and gesture capture systems - they aren't cheap, though). The RFID system will probably be the most ideal, depending on what the system is capable of in sample speed, and what kind of sample speed you need for your results.

If you come up with anything different, though - I would love to know about it; I've got an application in mind to develop that hinges on a similar need, and needs a very high sample rate (none of the above solutions would work for my need, unfortunately).
 
KJ6EAD said:
The RF Controls demo was slowed down so you could see how it works. You'd have to read the datasheet to see the specifications.
Click to expand...

I filled out their request form and downloaded it, and also read a number of other articles and papers on their site - I have yet to find anything about sample rate or accuracy; all I've been able to find have been the words "real-time" (which means nothing by itself), and in the datasheet, some blurb about "Location processor to SASL latency: ≤25ms"; I suppose this could mean - for a single SASL and one Location processor, that there could be 40 samples per second, and every additional SASL you add (up to 128) per Location processor reduces this accordingly (so if you were tracking 10 SASL, your sample rate would be 4 samples per second). If this is what it means, then it isn't too bad - but I don't think that's the "whole story" - there wasn't a lot of spec detail on this system (mostly marketing).


KJ6EAD said:
Ascension Technology has magnetic systems with a 7' range.
https://www.electro-tech-online.com/custompdfs/2011/08/TrakStarTransmitter-1.pdf
Click to expand...

AFAIK, Ascension doesn't have any wireless sensor solutions; all of their receiving sensors are wired. Though I really like their miniature sensors (I am wondering if I can get them for my old FOB kit - though I bet that even if I could, it would cost waaaaay more than I would be able to spend - LOL).
 
cr0sh said:
AFAIK, Ascension doesn't have any wireless sensor solutions; all of their receiving sensors are wired. Though I really like their miniature sensors (I am wondering if I can get them for my old FOB kit - though I bet that even if I could, it would cost waaaaay more than I would be able to spend - LOL).
Click to expand...

I thought that model was wireless. I guess not. That leaves optical or RF.

The RF Controls stuff would be fast enough for a reasonable number of rats unless they were moving very fast. The fact that their literature is mostly marketing instead of specification is worrisome but probably just means they tend to customize a lot or they're still looking for investment capital.
 
Acoustical location is possible in that space. Simply have small piezo speakers that chirp high frequency tones and multiple microphones, triangulate from the difference in time of arival. Would be very simple to implement, though tracking multiple targets might be a little harder, the transmitters on the rats could have receivers on them as well so that each rat collar could talk with the others to allow them to determine which transmitter gets to speak when. Seeing as how the space is so small you could use ultrasonic transceivers as well, the higher frequency the easier it is to filter on the electronics end.
 
Last edited:
KJ6EAD said:
I thought that model was wireless. I guess not. That leaves optical or RF.
Click to expand...

Unfortunately, it doesn't look like it; I was kind hoping it was, as I have an older flock-of-birds system and having no wires from the receivers to the interface box would be kinda sweet. It does look like they've managed to miniaturize the heck out of their receivers, though, to allow them to be used in ways that were impossible before, though. Maybe they are working toward wireless - I can see a possible few obstacles with the approach (mainly whether there'd be interference with the RF signal vs the tracking system, plus any latency issues that may cause drift or other mis-calibration over time).

KJ6EAD said:
The RF Controls stuff would be fast enough for a reasonable number of rats unless they were moving very fast. The fact that their literature is mostly marketing instead of specification is worrisome but probably just means they tend to customize a lot or they're still looking for investment capital.
Click to expand...

Assuming what I read was what it meant, then yeah - I agree; I personally think they don't mention much more than what I could find because they figure you've either seen it in action personally, and want a demonstration, or that you would call them and ask for a demonstration. Something tells me, with that kind of approach, that the system is anything but inexpensive. Ascension and Polhemus are the same way - I got my flock of birds as a "steal" via a seller on Ebay who had no clue what he was selling. I contacted Ascension about getting the maximum range transmitter cube, and just about dropped a brick at the price. They figure if you are interested, you know about what it going to cost.
 
Sceadwian said:
Acoustical location is possible in that space. Simply have small piezo speakers that chirp high frequency tones and multiple microphones, triangulate from the difference in time of arival. Would be very simple to implement, though tracking multiple targets might be a little harder, the transmitters on the rats could have receivers on them as well so that each rat collar could talk with the others to allow them to determine which transmitter gets to speak when. Seeing as how the space is so small you could use ultrasonic transceivers as well, the higher frequency the easier it is to filter on the electronics end.
Click to expand...

Ever play with interfacing the Nintendo PowerGlove (from Mattel) to a PC? Back in the mid-1990s, this was one of the "hacks" of the day to do (I had mine running first on my Amiga, then later a 486 - not too long back I dug it out and got it working with my then Debian box, using some drivers a guy wrote). One of the main problems with the system (actually, it had a lot of problems - it was a system well ahead of its time) was combating spurious reflected echos from hard surfaces in the vicinity of operation. The best solution was to mount it on a wall with some eggcrate or similar behind it (or in a pinch, a towel). Even with that, you had to have the receivers aimed right at the transmitter.

The problem with using high-frequency sound (or ultrasonics) is that it is highly directional (which is why it is used), and the transmitters and receivers have to be aimed at each other (or close to it) for it to work with any accuracy. What you'd want is an omni-directional high-frequency receiver (and I would put the receivers on the rats, because they are fairly passive devices - ultrasonic transmitters take a fair bit of current to ping the driver properly; the receivers can be lower powered), and multiple fairly directional transmitters - but I don't think I've ever heard of an omni-directional ultrasonic receiver (it seems like it would run counter to the way such a system works). If that does exist, and was small enough, then the system stands a chance of working...

Provided that any of the obstacles in the environment are transparent to the frequency of the system; any surfaces which would cause spurious echos or absorption of the pings will cause issues with tracking. This rules out anything too hard or too soft in the environment. Pretty much line-of-sight for there to be any accuracy.
 
Cr0sh, get your head out of your rear =) We're talking 25 FEET. Echo's are irrelevant unless the outside environment of the arena is more than 25 feet. The first signal received is the one that is direct line of site, ANY echo will take longer to reach the target, outside of possible retransmission issues of solid matter. This is not sonar 101, this is BASIC acoustical TOF triangulation. This is why you chirp instead of theorize on phase states with a continuous signal.

If the devices communicate and cooperate, this is a trivial matter of isolating the microphone from physical conduction and relying on the air to transmit the first recognized ping signal.

You're making this FAR more complex than it actually is.

Over 25 feet unless the transmitter is intentionally blocked and filtered out, it WILL be received.
 
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cr0sh said:
What kind of sampling speed are you looking for? Based on the demo video on the link KJ6EAD supplied, that RFID solution didn't look like it had a very high sample rate (several seconds per scan is what it looked like, but I couldn't find any further detail so it's difficult to say for sure).

Have you thought about optical tracking - that is, set up multiple video cameras, perhaps at the upper corners pointing downward, tracking (3D triangulation) retroreflective dots on the rats? The only problem with this scheme is not being able to identify each individual rat. Perhaps active IR dots, sending out a pulse code which could be decoded as part of the video stream? Another method might be to have addressable active IR dots, tracked by the cameras, each lighted in-turn via an RF link. Occlusion of the dots (whether passive or active) could be an issue, but with enough cameras to provide overlap, and proper design of the testing area (ie - no tunnels or tubes allowed, for instance), most problems could be overcome.

Another possibility might be a magnetic system - the rats pack would house a small coil (consisting of three orthogonal coils) that could be pulsed via addressable RF means, like the active IR dots above, and pickup coils on the walls and ceiling would determine X/Y/Z position based on magnetic strength (at issue here would be the battery life of the man-packs, plus the noisiness inherent in the system that would need to be filtered out, plus the need to build a non-ferrous environment, among other problems).

If you needed heading or other orientation data, then an RF link back from the man-pack from an on-board IMU might work well with the above ideas. A great issue to overcome, no matter what system, would be battery life for the man-packs (but may lithium ion batteries would help there).

I don't think, though, that you're going to find much off-the-shelf hardware for this kind of tracking (with the exception of an all-optical system - those are sold, though mostly as a passive system - for motion and gesture capture systems - they aren't cheap, though). The RFID system will probably be the most ideal, depending on what the system is capable of in sample speed, and what kind of sample speed you need for your results.

If you come up with anything different, though - I would love to know about it; I've got an application in mind to develop that hinges on a similar need, and needs a very high sample rate (none of the above solutions would work for my need, unfortunately).
Click to expand...

First of all, thank you all for your help with this.

As far as sample rate goes, I figure three samples per second being absolute minimum, the more the better. Preferably upwards of fifteen. I have considered optical/video tracking, but unfortunately some of the observation area will be outdoors, along with artificial light sources used on occasion. The idea of errant light causing problems puts me in a cold sweat, lol. In addition, each rat must be identified individually, and my sensors must be able to move (not during observation necessarily, but I will need to alter the area often enough that it won't be practical to re-key the relative position of each camera every time I will have to move one. I do, however, like the idea that the cameras are observation-only, and I wouldn't need to worry about the typical problems involved with RF circuits.

I do like the magnetic idea, but also unfortunately, the approach would suffer some of the same problems I would encounter with the camera based solution.

I do need orientation data, but I have located off-the-shelf (THANK GOODNESS) sensors with more than enough accuracy for the application. I plan to interface them to the control environment using dedicated data links, separate from the location system, whatever that ends up being. If this is a bad idea for some reason, I am more than open to alternative suggestions or ideas.

And finally, I would love to keep you posted. I am usually in the chat, instead of the forum, which is why my post count is low for the amount of time I've been a member. And, I would love to hear more about your idea, but I understand how things are with IP, and thus the need for secrecy in many cases. Even knowing the basic field of use for your application would interest me if that is possible to divulge.
 
cr0sh said:
I filled out their request form and downloaded it, and also read a number of other articles and papers on their site - I have yet to find anything about sample rate or accuracy; all I've been able to find have been the words "real-time" (which means nothing by itself), and in the datasheet, some blurb about "Location processor to SASL latency: ≤25ms"; I suppose this could mean - for a single SASL and one Location processor, that there could be 40 samples per second, and every additional SASL you add (up to 128) per Location processor reduces this accordingly (so if you were tracking 10 SASL, your sample rate would be 4 samples per second). If this is what it means, then it isn't too bad - but I don't think that's the "whole story" - there wasn't a lot of spec detail on this system (mostly marketing).
Click to expand...

I really need to fill out their form so I can paw through the info instead of bugging you all about their marketing specs :)
the system needs to be scalable, so I can add or remove sensors as the observation area is adjusted. I guess if a bunch of man-packs end up stuffed in an are that's in range of only a few sensors, the system will slow down. That's life I suppose, but hopefully the system will be amenable to me adding more sensor nodes to the bottle-neck area and resetting the system (of course, not during the observation) to reduce congestion. 128 tags will be sufficient, although I would like the system to be scalable to a much higher number, and of course if the sample rate decays as significantly as you theorized with the number of tags, the system won't support the number I need and maintain accuracy. Unless the number of sensors can be increased endlessly to handle a greater number of tags.
 
Last edited:
Sceadwian said:
Acoustical location is possible in that space. Simply have small piezo speakers that chirp high frequency tones and multiple microphones, triangulate from the difference in time of arival. Would be very simple to implement, though tracking multiple targets might be a little harder, the transmitters on the rats could have receivers on them as well so that each rat collar could talk with the others to allow them to determine which transmitter gets to speak when. Seeing as how the space is so small you could use ultrasonic transceivers as well, the higher frequency the easier it is to filter on the electronics end.
Click to expand...

I have considered briefly ultrasonic acoustic systems, but if I implement them, they will have to be secondary, as I cannot handle the potential problems associated.
 
alec_t said:
Are you anticipating the rats will breed?
Click to expand...

LOL, no. But I may have to alter the observation area/number of rats, and I want that to be very easy and simple. Plus, not all of the tagged objects will be rats, some will merely be inanimate, mobile objects in the observation area. If the system would be capable of supporting, say, 5000 tags and 500 stationary transceivers, I would be thrilled, so I wouldn't have to worry about later expansion. But I would definitely not use that many at first.

Mr RB said:
RFID tags and lots of RFID sensors around the environment?
Click to expand...

That's the idea I'm looking at, apparently (I didn't know at the time), several companies vend such systems, KJ6EAD was kind enough to tell me about one. I had been looking, but apparently entered the wrong keywords.
 
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