VL53L1X People Counting ROI center

[HMull.1]

I am implementing an “auto calibration�? of the ROI in my people counting algorithm based on the one provided by ST. The program defines the centers of the two zones used to detect entry/exit in an area. Currently I run a simple detection algorithm to measure repeatable accuracy of distance measurements. I tweak the ROI sizes until I find the best accuracy but I do not change the center coordinates. These values are constant and still the same as the values ST provided in their example.

I want to know if those values are indeed constant or should I adjust them as part of the calibration? I’m wondering if the ROI size is set to an uneven number..does that mean the zone will not be symmetrical about its center?

Thanks!

[John E KVAM]

If you choose an even ROI size, the center SPAD is the one either up, to the right or both of the ideal center location.

The hardware will figure it out.

With people counting the trick is to insure you can see a person in one zone without having them be in both zones.

Feel free to tweak whatever you need too, but a smaller zone will range less far than a larger zone.

• john

[HMull.1]

Thank you for your reply.

The "calibration" is more just a determination and optimization of how accurate the selected ROI returns.

These are the center coordinates:

int center[2] = {167,231}; // these are the spad center of the 2 8*16 zones

I just want to try and understand what these values mean in practice. Are they constant? Factory calibrated? How I see it is if I make the ROI too small and keep these values constant, I run the risk of creating a "dead zone" between the two ROIs. Is that correct? So if I want to create for instance two 4 x 4 ROIs but don't want a dead zone, I imagine I should adjust the center coordinates to bring these two ROIs closer to one another.

[John E KVAM]

Go to st.com and look for UM255. If you use the UltraLite driver on the VL53L1X, it will explain all.

the SPAD array is a 16x16 array with a numbering system that only makes sense to a hardware designer.

Those two numbers are just a location within the array.

• john