Time delta to compute proper velocity values?

API, R&D and Technology
1

The description here says that

Deltas reports changes of coordinates, force, and area between frames.

However, I do not see a way to scale this relative to the actual time interval between the frames (I don’t know how much time passed between frame scans).
To my understanding, time between scans can vary depending on factors such as scan resolution or just jitter due to non-rt access to the sensel (?).

A sensual place for such information would IMHO be SenselFrameData but I cannot find anything like this there.

Here’s what I try to get:

double deltaTime = /* time between two frame scans in seconds */;

float velocity_x = frame->contact[0].delta_x * deltaTime; // in mm/sec

Am I missing something obvious? Thanks for your patience!

2

Hi there,

Sorry for the delay on getting back to you on this. In short, we do have a timestamp that is sent over from the Morph (https://github.com/sensel/sensel-api/blob/1139c84b35837dce94f49ef926ca5e9d55693fd7/sensel-lib/src/sensel_device.h#L84) but we have not exposed it because it is not a reliable clock. As a result, we do not plan to expose the timestamp at this time.

Really appreciate your continued work!

3

Thanks for getting back to me on this issue.

I guess, I can use that time stamp, no matter if you “exposed” it?

A time stamp seems to be very crucial since I measured a reasonable amount of jitter between frame reads on my end of the API…

Maybe your dev-guys could tell me how jitter-y the actual frame reading is, and hence how much the delta-values are prone to time-related jitter?

cheers and thanks!