example of Metavision::Histo3dDecoder use?

[skal-hs]

Hi,

i'm trying to use the Histo3dDecoder with:

 std::unique_ptr<Metavision::Device> device = Metavision::DeviceDiscovery::open("");
 auto* decoder = device->get_facility<Metavision::Histo3dDecoder>();

but i get this compile error:

/usr/local/include/metavision/hal/device/device.h:32:23: error: static assertion failed due to requirement 'std::is_base_of<Metavision::I_RegistrableFacility<Metavision::Histo3dDecoder, void>, Metavision::Histo3dDecoder>::value': Unable to get facility of unregistrable facility type.
   32 |         static_assert(std::is_base_of<I_RegistrableFacility<FacilityType>, FacilityType>::value,
      |                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
camera_tuner.cpp:191:41: note: in instantiation of function template specialization 'Metavision::Device::get_facility<Metavision::Histo3dDecoder>' requested here
  191 |     auto* i_histogram_decoder = device->get_facility<Metavision::Histo3dDecoder>();

Is it expected? What code am i missing here?
Is there any example of EHCDecoder usage somewhere?

Thanks a lot!
skal/

[lbristiel-psee]

Hello @skal-hs

the proper way to instanciate the Histo3D events decoder is the following:

#include <metavision/sdk/base/events/raw_event_frame_histo.h>
#include <metavision/hal/facilities/i_event_frame_decoder.h>
auto* decoder = device->get_facility<Metavision::I_EventFrameDecoder<Metavision::RawEventFrameHisto>>();

The only example we have in the SDK that leverage this decoder at the moment is within the Stream module:
https://github.com/prophesee-ai/openeb/blob/main/sdk/modules/stream/cpp/src/camera_live.cpp#L247

Hope this helps,
Laurent for Prophesee Support

[skal-hs]

Hi Laurent,

thanks for the pointers.

I've tried to use it similarly to the test psee_raw_file_decoder_gtest.cpp
This test passes ok, and the same code transposed to my app works too.

But if i replace the test's code device = DeviceDiscovery::open_raw_file("./histo3d.raw", cfg); by the one actually opening the real camera: device = DeviceDiscovery::open(serial);, then it stops working.
The callback dealing with the histogram is not called.

-> Is the I_EventFrameDecoder<RawEventFrameHisto> facility really using the hardware EHC, or is just suitable for histo3d RAW files?
And if the latter, how can i access the real hardware EHC histograms?

thanks!
skal/

[lbristiel-psee]

Hi,

EHC is only available with the GenX320 sensor (https://www.prophesee.ai/event-based-sensor-genx320/). If you own a camera that does not contain this sensor (but rather an IMX636 for example), then no ECH is present and no Histo3D data will be produced.

If you do own a GenX320 based product, then you can ask access to Prophesee Knowledge Center (https://www.prophesee.ai/resources-access-request/) where will can access the GenX320 Datasheet and User Manual that explain how to configure EHC.

Best,
Laurent for Prophesee Support

[skal-hs]

Laurent,

yes, i have the GenX320 on EVK3. That's why i was a bit surprised: i was expecting to be able to test the feature with OpenEB before having to resort to using the hardware registers directly, as described in the document.

skal/