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Re: comments on basic framework draft

From: Andy Gryc <AGryc@qnx.com>
Date: Mon, 20 Jan 2014 16:12:10 +0000
To: "Gerken, Stephen" <sgerken@jaguarlandrover.com>, "public-autowebplatform@w3.org" <public-autowebplatform@w3.org>
CC: Grant Courville <GCourville@qnx.com>, Tina Jeffrey <tjeffrey@qnx.com>
Message-ID: <CF02B307.400D7%agryc@qnx.com>
Thanks so much Stephen, I'm very glad that you helped fill out the discussion we had on Tuesday.

I completely agree with your comments regarding bitfields and how they may not work for the purpose of extendability—I mentioned the same concern on the call. The concept of lists will be needed elsewhere too, so I think it's important that they are supported. For example, in the QNX piece that I added types & ranges too, the same need for lists came up in describing door configurations. I'll have to leave it up to Kevron, Justin and anyone else WebIDL-expert who wants to chime in (Paul? Aldric?) on precisely how we would implement it.

I'm not sure what the right representation of zone would be, but thank you so much for your use cases. They will greatly help us in figuring out a proper representation.

From: <Gerken>, Stephen <sgerken@jaguarlandrover.com<mailto:sgerken@jaguarlandrover.com>>
Date: Friday, 17 January, 2014 4:29 PM
To: "public-autowebplatform@w3.org<mailto:public-autowebplatform@w3.org>" <public-autowebplatform@w3.org<mailto:public-autowebplatform@w3.org>>
Subject: comments on basic framework draft
Resent-From: <public-autowebplatform@w3.org<mailto:public-autowebplatform@w3.org>>
Resent-Date: Saturday, 18 January, 2014 5:17 PM

Hi all,

Below please find comments on the basic framework draft as found at https://raw.github.com/tripzero/automotive-bg/master/vehicle_spec.html as of 17th January 2014.

The general appearance of the document is consistent with expectations for a W3C standard.  The document is well laid out and well organized.

The concept of "zone" as presented in the draft appears to be an attempt to capture the concept that multiple sensors on a vehicle will report data of the same data type, and that within a group of such sensors reporting on a common data type, it may be useful to distinguish individual sensors from one another on a basis of physical location.  While the underlying concept is sound and worthwhile, the particular implementation of "zone", as detailed in the draft, is incomplete.

As drafted, "zone" is a solely planar distinction, with bitfielded values for front/mid/rear, left/center/right.  For some vehicle equipment, this division may be sufficient; many passenger car models have four wheels, four seats, and four or five doors, which can be adequately described as a wheel in the front right zone, a seat in the rear left zone, or a door in the center rear zone (a hatchback).  However, even with these mundane examples, zones as currently described do not adequately disambiguate equipment.  Some full-size pickup trucks have dual rear wheels; for such models, "tire pressure on wheel in right rear zone" describes two pressure sensors, one for each of the dual right rear wheels.  We should not assume that no future vehicle with dual wheels will be a passenger car.

Additionally, other equipment types will not disambiguate easily in a planar zone concept.  For example, existing JLR models have up to 24 camera views.  Some cameras may be front-mounted but side-facing, while others may be front-mounted but rear-facing.  There may be camera clusters in which many cameras share a common mount point, for example in the rear right quadrant, and for which the cameras are distinguished from one another by view angle, view direction, spectrum of sensitivity, resolution, or other factors not contained in a planar zone concept.  Generally, equipment types for which a planar zone does not adequately locate a single sensor include:
 + microphones, which may have multiple vertical placements within a given planar zone;
 + microphones, again, in that two mics in close physical proximity may have different sensitivities;
 + audio speakers, which may have multiple vertical placements within a given planar zone;
 + audio speakers, again, for which woofers and tweeters may share a planar zone;
 + tire pressure, in the case of dual wheels mentioned above;
 + accelerometers, which in addition to physical location, also have axes of sensitivity;
 + cameras, which may have differences of view angle, view direction, spectrum, and resolution as discussed above;
 + airbags, for which a right front zone may have multiple airbags located in a body pillar and in the roof, collectively forming a side curtain, and also an additional airbag located in the front of the right front zone in the dash.

In light of the above examples of the diversity of sensors in modern vehicles, and bearing in mind the creativity of current and future automotive engineers, it would seem prudent to permits manufacturers to specify bases for disambiguation of equipment which are not restricted to a purely physical planar location, or even to a predetermined set of bases of which we are currently aware.

As a technical point on the specific implementation of Zone, the current implementation is as a bitfield.  This means Zone exists as a single field within the interface, which is masked against predefined constants in order to extract information from that field about which specific zones are on or off.  Effectively, the Zone field carries information as a fixed-length array of boolean values, where the array length is either 16 (for a short, as currently defined) or 32 (if altered to a long). With either 16 or 32 maximum possible masks, it is entirely possible that the number of actual useful bases of disambiguation would exceed the array length, leading to an awkward overlaying situation; if this data type is for microphones, 0x80 means speech spectrum, but if this data type is for speakers, 0x80 means tweeters.  While subtyping the zone masks based on the data type is a possible means of extending the zone space beyond 16 (or 32) values, this approach is awkward to document and difficult to code correctly, and should be avoided if possible.

It would be preferable for Zone to be an actual array, not a bitfield.  If Zone were an actual array, it could still be an array of ints, but since masks wouldn't be necessary, the number of meaningful values of those ints could be 2 ^^ 16 instead of 16.  So for example:
const short Front = 0x0001;
const short Middle = 0x0002;
const short Rear = 0x0003;
const short Left = 0x0004;
const short Center = 0x0005;
const short Right = 0x0006;
const short Xaxis = 0x0007;
const short Yaxis = 0x0008;
const short Zaxis = 0x0009;
const short MfgBase = 0x8000;
const short JLROuter = MfgBase + 0x0040;
const short JLRInner = MfgBase + 0x0041;
VehicleCommonDataType{ ... readonly attribute Zone[] zone; ... }...
such that a returned instance tpres of VehicleTirePressureDataType has tpres.zone[0] == Rear, tpres.zone[1] == Left, tpres.zone[2] == JLRInner.

Also, as a minor copyediting detail, the word "information" in the draft is variously misspelled as "inforomation" and "Infomration".

Generally however it's clear that a lot of effort and thought has gone into bringing the document to it's current draft state, and there is good material here which is worth building upon as the scope of the document is fleshed out.

Steve Gerken
Linux Developer
MSX, as broker for Jaguar Land Rover

One World Trade Center, 121 SW Salmon Street, 11th Floor, Portland, Oregon, 97204
Email: sgerken@jaguarlandrover.com<mailto:sgerken@jaguarlandrover.com>
Received on Monday, 20 January 2014 16:12:41 UTC

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