Analytics on edge devices
So far the OSQL models in the tutorial were developed and run on an sa.engine stream server (SAS) running on some computer accessed from sa.studio. If you are running sa.studio Desktop the SAS will run on your PC. If you are running the sa.studio 'sandbox' it will run in a Docker container in some cloud. The computer where your SAS is running is called the server computer.
Do not mix up the abbreviation SAS with the contemporary concept SaaS. A SAS is simply an sa.engine server to which other sa.engine clients and servers are connected.
This tutorial will show how to develop and run models locally on edge devices. To do this you need to first install an edge client (EC) on your device. An EC is also an sa.engine system, but with more limited capabilities than a SAS.
Once installed and started the EC can be registered in a SAS so that sa.engine users and applications know about its existence. The communication protocol between ECs and SASes is internal to sa.engine so that users need not know any details.
The system supports a TCP based communication protocol out-of-the-box. However, sa.engine is agnostic to the communication infrastructure and several other communication protocols are available as plug-ins. Furthermore, plug-ins for new ones can be implemented.
An EC can send up internal messages north to its SAS for evaluation, thus acting as a client to the SAS. In particular it can send up a message to register itself. It can also send up a message indicating that it is ready to process local tasks from the server, in which case the state of the EC is said to be active. Edge clients can also be inactive, which means that they currently will not be able to execute messages from the server, but they still can execute CQs locally. They can also be busy when they cannot accept any new tasks, usually because other tasks use all their resources.
We will first show how to run the model named my_c_to_f in Saving
data and models in your SAS on
the server computer. Then we will do the same for an edge client
installed on an Android device.
Finally, we will develop a new model called detect-shake that uses
the accelerometer on the Android device.
Edge clients on PCs
As a first step, we ship the model my_c_to_f to an edge client
running on the server computer.
In sa.engine Desktop the function call start_edge('edge1') will
start and register a new edge analyzer peer named edge1 on your
server computer. However, this call is not allowed when you run the
'sandbox' in studio.streamanalyze.com. We have therefore already
started an edge named edge1 there.
Now we can deploy the model my_c_to_f on edge1 by evaluating:
models:deploy(["edge1"],"my_c_to_f");
To run this code block you must be logged in and your studio instance must be started.
The function returns the string "EDGE1" when the system has
successfully deployed the model my_c_to_f in the edge client named
edge1.
Now, if you click server > in sa.studio you get a pull-down menu to
choose which peer to send the CQs to. In this case the peer is either
the SAS (server) on your server computer or the new edge client
edge1. Choose edge1 to drill down to edge1.
The function this_peerid() returns the name of the peer:
//peer: edge1
this_peerid()
To run this code block you must be logged in and your studio instance must be started.
It should return "EDGE1" if you have successfully drilled down to
the edge client edge1 and "SERVER" is you are connected to your SAS.
Let's try running ctof() on edge1:
//peer: edge1
ctof(32)
To run this code block you must be logged in and your studio instance must be started.
You can also ship queries to edges from the stream server (or even
from other edges) by using the built-in function edge_cq(Charstring
edge, Charstring cq) -> Stream, which evaluates the CQ string cq on
edge.
For example, run this in the server:
edge_cq('edge1','ctof(72)')
To run this code block you must be logged in and your studio instance must be started.
Here the query ctof(72) is shipped to edge1 for
evaluation and the result stream is shipped back
to the stream server for real-time visualization by sa.studio.
Registering an Android edge client
This part of the tutorial needs an edge-device with audio
capabilities. The easiest way to get this is to download and run the
Android Edge Client app and
register it in your SAS under the name android1. You can
also install an edge client app on some other kind of device having
audio capabilities such as a laptop or a Raspberry pi. To learn how to
install on different devices take a look at Installation.
If you are running this tutorial in the 'sandbox' you should go back to Querying the microphone now and go through the steps there.
We are now ready to deploy the audio model on your Android device.
In sa.studio on your PC drill down to the android1 edge client and
evaluate:
//peer: android1
this_peerid()
To run this code block you must be logged in and your studio instance must be started.
The query will return the string "ANDROID1" if the device runs
the edge client app on your Android device.
You can now deploy the audio model on android1 by calling the
function models:deploy() in your SAS:
models:deploy(["android1"],"audio")
To run this code block you must be logged in and your studio instance must be started.
It will return the string "ANDROID1" when the model has been
successfully deployed on the device. The audio model is now
permanently installed in the local edge client database on your
Android device.
You can now run audio_band() on your Android device by calling:
//peer: android1
audio_band(70, 700)
To run this code block you must be logged in and your studio instance must be started.
Restart the edge client on your device and verify
that the function audio_band() works as before.
Developing the detect-shake model
In this section we will develop a model directly on your edge device. The following will be covered:
Finding out what signals an edge device has and what registered edge devices have a specific signal.
Running a CQ producing a stream of raw data from a signal on an edge device.
Using the raw signal stream in a model running on the device to detect whether it is shaking or not.
Device Signals
Before defining a model on an edge device to analyze signal readings, we first need to obtain information about what signals are available on your device. Then we can use this information to formulate CQs and define models analyzing signals on it.
Run the following query to get the available signals on you Android device:
//peer: android1
signals()
To run this code block you must be logged in and your studio instance must be started.
The query returns a set of the names of all signals on the device.
Here one of the signals is named "accelerometer". To ask what devices have an accelerometer you can issue this query to the SAS:
edges_with_signal("accelerometer")
To run this code block you must be logged in and your studio instance must be started.
It returns a vector of all registered edges having an accelerometer.
Analyzing the accelerometer stream
In order to get a stream of data from a signal on a device the
function signal_stream(Charstring sn) -> Stream of Vector is called. It
returns a stream of measurements for the signal named sn on the
device. For example, to retrieve the accelerometer readings on edge
android1 we can send it this CQ visualized as a line plot:
//peer: android1
signal_stream("accelerometer")
To run this code block you must be logged in and your studio instance must be started.
A stream of 3D gravitation vectors are returned. Test it by rotating the device.
Use the gyroscope instead of the accelerometer.
The gravitational acceleration can be calculated by taking the magnitude of each gravitation vector in the stream from the accelerometer:
//peer: android1
select Stream of sqrt(sum(g .^ 2))
from Vector of Number g
where g in signal_stream("accelerometer")
To run this code block you must be logged in and your studio instance must be started.
When the device is resting the query returns numbers close to the earth's gravitational acceleration (9.81). How close depends on the precision of the sensor.
The CQ above will be used in the detect-shake model. First we
define a helping function gravity_acceleration():
create function gravity_acceleration() -> Stream of Number
as select Stream of sqrt(sum(g .^ 2))
from Vector of Number g
where g in signal_stream("accelerometer")
To run this code block you must be logged in and your studio instance must be started.
One way to get a sense on how much a device is shaking is by
calculating a stream of running standard deviations over sliding
windows in gravity_acceleration().
Example:
//peer: android1
stdev(winagg(gravity_acceleration(),50,5))
To run this code block you must be logged in and your studio instance must be started.
The more the device is shaking, the larger standard deviation.
This stream of standard deviations will serve as the main part of the
detect-shake model. The following CQ returns the shake state 1
when the device shakes (standard deviation larger than 5) and 0
otherwise, visualized as a line plot:
//peer: android1
select Stream of shakes
from Number shakes, Number elem
where elem in stdev(winagg(gravity_acceleration(),50,5))
and shakes = case when elem > 5 then 1
else 0 end
To run this code block you must be logged in and your studio instance must be started.
To investigate how the shake state depends on parameter settings, we
define a function shake_state() taking the standard deviation
threshold, window size, and window slide as arguments:
//peer: android1
create function shake_state(Number threshold, Number size, Number stride)
-> Stream of Number
as select Stream of shakes
from Number shakes, Number elem
where elem in stdev(winagg(gravity_acceleration(),size,stride))
and shakes = case when elem > threshold then 1
else 0 end
To run this code block you must be logged in and your studio instance must be started.
Example:
//peer: android1
shake_state(5, 50, 5)
To run this code block you must be logged in and your studio instance must be started.
We only need to know when the shake state changes, which will drastically reduce the stream volume by only emitting values when it changes. For this we can use the system function:
changed(Stream s) -> Stream
It removes from stream s elements that are equal to their
predecessors.
Example:
//peer: android1
changed(shake_state(5, 50, 5))
To run this code block you must be logged in and your studio instance must be started.
Investigate how shake_state(threshold,size,stride)
behaves with varying threshold, size, and stride. What is the
effect of a smaller window? What is the effect of a larger stride?
After some experiments we define the final function
shakes(threshold) with fixed size and stride as:
//peer: android1
create function shakes(Number threshold) -> Stream of Number
as changed(shake_state(threshold, 50, 5));
To run this code block you must be logged in and your studio instance must be started.
We are now ready with the local shake detection model running on a single Android device!
Try it:
//peer: android1
shakes(5)
To run this code block you must be logged in and your studio instance must be started.
Create a model named detect-shake
and store in its master file the functions gravity_acceleration,
shake_state, and shakes.
In the next tutorial we show how to store and query data in the built-in object-oriented database system.