# Problems with DS-015

**URL:** <https://forum.opencyphal.org/t/problems-with-ds-015/1219>\
**Category:** General\
**Created:** [May 2, 2021, 10:28pm UTC](https://forum.opencyphal.org/t/problems-with-ds-015/1219 "2021-05-02T22:28:37Z")\
**Posts on this page:** 1\
**Showing post:** 11

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**Author:** ![tridge](https://forum.opencyphal.org/user_avatar/forum.opencyphal.org/tridge/32/119_2.png) [@tridge](https://forum.opencyphal.org/u/tridge)\
**Post date:** [May 3, 2021, 8:27pm UTC](https://forum.opencyphal.org/t/problems-with-ds-015/1219/11 "2021-05-03T20:27:57Z")

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> [@dagar](#):
>
> I propose we add services for handling these simple sensor types, and leave things like “air\_data\_computer” as aspirational examples

yes, we should have simple ones that just reflect the real data. I don’t think we should add the “air\_data\_computer” unless there is going to be real hardware that will really be used that needs it.

> [@](#):
>
> It would also be nice to make the covariances optional in these messages.

we should just stop using covariance matrices. It just encourages developers to make up meaningless numbers. We shouldn’t be wasting bandwidth on stuff that is just made up.  
A few guiding principles in message design:

- don’t add fields unless there is a real need for them
- don’t add fields that force the developer to make stuff up that they don’t really know

> [@dagar](#):
>
> For reference, here’s what an earlier version of DS-015 had for differential pressure.

closer, but should remove a bunch of fields.

- I don’t think the timestamp really has value on this message. Timestamps have enormous value on messages like GNSS position and velocity, but on differential pressure used for airspeed I don’t think it is useful. The time of arrival is fine.
- remove both filter\_delay and the filtered differential pressure. It would only make sense if we were greatly reducing the sample rate on the bus and I don’t think we are likely to be doing that.
- get rid of the variance, as the sensor is unlikely to really have a good measure of that
- only have one temperature

We should aim to get it down to a single CAN frame if possible.

> [@](#):
>
> The nice thing about UAVCANv1 is you don’t need the service to start or do something custom, you can directly publish a dynamic pressure ( `reg.drone.physics.thermodynamics.PressureTempVarTs` ) on your own subject

but that doesn’t tell you what this reading actually is. It just says it is a difference between two pressures and a temperature (plus a pointless timestamp and covariance). We need it to be broadcast in a form that says “this is from a pitot tube, if you want to get a pitot based airspeed you can use this”.

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