Smartphone as digital survey device?

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Smartphone as digital survey device?

Postby rlboyce » Mar 9, 2014 1:33 pm

I have been thinking of getting a DistoX2. The main problem with a DistoX2 is... it's not cheap at all. I might find myself spending $500 or more before it's all said and done.

Then I began to realize that I already have a device which contains an accelerometer, gyroscope and magnetic sensor... my Android smartphone! Wouldn't it be cool if I didn't have to spend money at all? Or maybe just spend a fraction of that $500 to bring my smartphone up to standards?

So, here are the two questions that I hope you guys are able to help me answer:

  • How accurate/precise can I expect readings from my smartphone to be?
  • Is there a way I can determine the accuracy/precision before investing time and effort into developing an app?
  • How hard would it be for a caver with no app development experience to make a compass/inclinometer app?
  • Does such an app already exist?
Some of the disadvantages of using a smartphone are:

  • Battery usage (smartphones are power hungry)
  • No distance measurement
  • Cost of cave-proofing (Otterbox case)
  • Need to mount a laser (in a way that didn't affect the sensors)
Some of the advantages of using a smartphone are:

  • Potentially cheaper than a DistoX2 (since I already own the smartphone)
  • You don't need a separate PDA to sketch with... just sketch with the smartphone! (assuming it was stylus compatible)
  • Plenty of storage space
  • Voice technology (no need to push buttons)
If we could get a nice survey app for smartphones to work, cavers (or even non-cavers) around the world could use it.
Happiness can be measured in mud/in².
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Re: Smartphone as digital survey device?

Postby caver.adam » Mar 9, 2014 4:04 pm

From what I have seen, the compass on most smartphones is within +/- 5 degrees. You might see some within +/- 3 degrees. Most cave surveyors stick to +/- 1 degree (backshot must be less than 2 degrees off from front shot).

Lots of apps exist such as Theodolite for iPhone.

Also, mounting a laser is difficult because you need your laser to be centered on the axis of the compass/clino.

It would definitely be cheaper than a DistoX2...but if it was easy and accurate to do on a smartphone Beat wouldn't have bothered with his device.
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Re: Smartphone as digital survey device?

Postby caver.adam » Mar 9, 2014 4:05 pm

Check out project Tango for what you are looking for: https://www.google.com/atap/projecttango/
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Re: Smartphone as digital survey device?

Postby rlboyce » Mar 9, 2014 5:41 pm

Thanks for the input Adam. You make some good points. I'm not sure I agree that it hasn't been done before because it is hard and inaccurate. : )

I think what I need to do is find some sort of datalogger for these internal sensors, then do a couple of test orientations. Once I have the data, it shouldn't be too hard to determine the precision values. I can then compare the data with Suunto readings to determine accuracy.
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Re: Smartphone as digital survey device?

Postby Radiolocation » Mar 9, 2014 9:47 pm

It will require calibrating all 3 axis of the smartphone's accelerometer and magnetometer in many directions and rotations, and aligning them with the laser that you have mounted, and you still don't have range. I recently put a DistoX2 together and did the 56 point calibration. I have used Disto A3s, which are great, but the X2 is smaller, waterproof, won't require frequent recal, and you simply hold the button down until the shot is completed, just like the trigger on a gun. This greatly reduces hand shake.
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Re: Smartphone as digital survey device?

Postby caver.adam » Mar 9, 2014 10:16 pm

Some work has been done. Looking at a teardown of the Galaxy S4 we see that it uses an ST LSM330DLC for acceleration and gyro and a AK8975C e-Compass. The AK8975C has a resolution of .3uT. It is hard to tell from their data sheet what sort of error is in their reading. From this I would expect you to be able to get +/- 2 degrees from this sensor in Kentucky. If you are much closer to the equator or to the poles you will get less accurate than this.

Your real problem is going to be calibration. You will have to remove the battery and replace it with a non-magnetic battery. You will have to remove any variable "soft iron" sources of magnetic fields near the sensor. And you will need to make sure you have a good hard iron calibration. Even with this you will have to test calibration as part of your design.

I've put together a compass based on the LSM303DLHC which has a .2uT resolution, but at best I am getting a +/- 1.5 degree accuracy. Although I have a couple more things to try before I pass judgement.

If you put together a report with good information on accuracy, repeatability, and calibration drift...people will be interested in seeing it.
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Re: Smartphone as digital survey device?

Postby gindling » Apr 18, 2014 12:16 pm

Here is a link to an article about the Google DIY Endo phone.
http://venturebeat.com/2014/04/10/googl ... ule-bible/

Its like building a phone with legos but each piece is it's own device like different cameras, battery sizes, flash, etc. It will be interesting to see how well it works and if any industrious and engineering cavers will make surveying blocks to turn it into a digital survey device.
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