# FAQ¶

## General¶

### What kind of data do we get from a Prophesee sensor?¶

Contrast Detection (CD) events can be acquired from a Prophesee sensor. They represent a response of a pixel to a change of illumination and are of 2 types:

• CD ON events correspond to positive change : from dark to light

• CD OFF events correspond to negative change : from light to dark

For more information, check our pages on event-based concepts and events streaming and decoding.

### Can I record data from supported cameras? Which format is used for data recording?¶

You can record data with Metavision Player. By default, data are recorded to RAW format. However, Metavision Player allows you to export your recording in AVI format.

Alternatively, you can use the application Metavision Viewer to record RAW files. As you have an access to the source code of this application, you can see the Metavision SDK in use and even enhance it to fit your needs.

In addition, you can convert RAW files to the following formats:

### How do I know what is the event encoding format of a RAW file?¶

You can find the EVT format (EVT2 or EVT3) of your RAW file by one of those methods:

### How can I check the duration and the event rate of my RAW file?¶

You can use metavision_raw_info application:

metavision_raw_info -i YOUR_FILE.raw


### How can I read IMU data with Metavision?¶

Some of Prophesee products are able to record IMU (Inertial Measurement Unit) data along with the sensor native data stream. This IMU is not part of our sensors but is mounted on another board (Invensense MPU-9250) within some of our EKVs. Until version 2.0.0, IMU was supported in metavision, but this feature was not leveraged by any of our partner’s camera, so we decided that supporting it was note relevant for us and we removed it since version 2.1.0 of metavision.

If you want to use the IMU or if you have RAW files that contain IMU data that you want to decode, the easiest way is to use Metavision 2.0.0. Please contact us to have access to this release.

If you want to read IMU data with the latest version of Metavision, you will have to program your own events decoder. In that case, contact us so that we communicate the format of those events.

### How can I retrieve information on installed Prophesee software?¶

You can retrieve the information on the installed software and their versions with these applications:

### How can I retrieve information on plugged cameras?¶

You can retrieve the information on the plugged cameras with metavision_platform_info application.

metavision_platform_info


### What kind of extension USB cable should I use for my camera?¶

If the USB cables provided with the camera is too short for your use, you will have to use an extension cable, but you have to be careful as you will quickly reach the USB specs length limits for the support of USB 3.0 super speed. Hence, we recommend to use to use an active USB 3.0 extension cable with an external power supply. Here is an example of such a cable: StarTech.com Active USB 3.0 Extension Cable with AC Power Adapter

### To avoid flicker events, which non-flickering light source should I use?¶

The best non-flickering light source is any halogen lighting. If you want LED source, you must double check it is not flickering (lots of them are using PWM modulation for dimming, and produce flicker). We successfully used Dracast Camlux Pro Bi-Color.

### Can I use a Virtual Machine (VM) to work with my camera?¶

Prophesee cameras require USB 3.0, and due to limited support of USB 3.0 by Virtual Machines, your display and USB will not perform as expected, therefore we do not recommend using Virtual Machines.

## Troubleshooting¶

### How can I fix “Entry Point Not Found” when launching Metavision applications on Windows?¶

When running Metavision applications on Windows, you may hit the following error message: “Entry Point Not Found. The procedure entry point inflateValidate could not be located in the dynamic link library C:\Program Files\Prophesee\bin\libpng16.dll.”

This means Metavision’s version of libpng is incompatible with some other libraries of your installation. Most probably, there are multiple copies of zlib1.dll in your installation and the first one found by Windows is not ours.

First, check if multiple zlib1.dll can indeed be found in your installation. For this open an explorer and search for zlib1.dll. You should at least have one result in the folder C:\Program Files\Prophesee\third_party\bin

If you find multiple results, you need to reorder your Path environment variables and move Prophesee Paths first. Here is one way to do it:

• open the start menu

• search environment

• select edit environment variables of the system

• click environment variables

• in system variables, locate Path

• edit and reorder the environment variables to have Prophesee Paths at the top

### How can I fix the error ‘the code execution cannot proceed because msvcp140.dll / msvcp140_1.dll was not found’ on Windows?¶

During installation of Metavision Essentials on Windows, we check the presence of MS Visual C++, and we rely on the registry to know if the libs are there or not.

It seems that the uninstall of the previous MS Visual C++ Redistributable was not done properly (without any visible error), and you could end up with a registry value without the installed software. In this case, the installation of Metavision Essentials on Windows could miss MS Visual C++.

To fix the issue, please check if the MS Visual C++ Redistributable is installed. If not, then install it properly.

### Why do I get the warning ‘Please now unplug your camera’ when using EVK 2 on Windows?¶

This warning is shown at the end of the execution of an application that connects to an EVK 2 on Windows. This is the expected behaviour with the current version of our camera plugin. It does not mean that there was a problem during the program execution, but it asks you to unplug/replug your camera before launching another execution. We plan to enhance this behaviour in a future release to avoid this manual operation.

### How can I fix the error ‘Failed to load module “canberra-gtk-module”’ on Ubuntu?¶

Install the package required to display videos, as mentioned in the installation tutorial:

sudo apt -y install libcanberra-gtk-module


### How can I fix the error ‘error while loading shared libraries: libc10.so’ when launching metavision_detection_and_tracking_pipeline on Ubuntu?¶

This error is due to the fact that libtorch library is not found.

To run the application metavision_detection_and_tracking_pipeline, follow our guide.

Essentially, you need to:

• install libtorch in a LIBTORCH_DIR_PATH folder (see our section on additional dependencies to install for ML).

• reference this path when launching the sample. For example on Linux:

LD_LIBRARY_PATH=<LIBTORCH_DIR_PATH>:$LD_LIBRARY_PATH metavision_detection_and_tracking_pipeline -h  ### How can I fix the error ‘No plugin available for input stream. Could not identify source from header’ when reading RAW files?¶ This error message can occur when trying to read a RAW file, for example with Metavision Player: $ metavision_player -i /path/to/my_file.raw
[HAL][ERROR] While opening RAW file '/path/to/my_file.raw':

terminate called after throwing an instance of 'Metavision::HalException'
what():
------------------------------------------------
Metavision HAL exception
Error 101000: No plugin available for input stream. Could not identify source from header:
% Date 2021-02-03 11:53:21
% integrator_name Prophesee
(...)
------------------------------------------------


This problem can have multiple causes:

• the Camera Plugins are not installed. Prophesee Camera Plugins are installed automatically with Essentials, but if you are using OpenEB or Professional, then you need to install the plugins manually (follow the instruction for Linux or Windows).

• the Camera Plugins are not found. If you installed third party plugins or compiled plugins yourself, you need to specify the location of the plugin binaries using the MV_HAL_PLUGIN_PATH environment variable (follow the instruction for Linux or Windows).

• the RAW file is not recognized. the RAW file header contains ASCII information that is used to detect what plugin to use when opening the file with Metavision. If this header is missing some required metadata, opening the file will fail. For example, the error No plugin available could be caused by a missing or malformed plugin_name in the header. Hence, it’s good practice to check this header with a text editor when hitting this error, and fix it if needed. Note that the application metavision_raw_info prints some information about the RAW file (including the plugin_name) that could help fix the RAW file. Finally, if you have multiple RAW files to update, contact us so that we can provide you with a script.

### How can I change the logging level at runtime?¶

Metavision uses its own logging mechanism with four levels: TRACE, INFO, WARNING, ERROR. Any message that has a higher or equal level will be enabled to pass through, and any message that has a lower level will be ignored.

The default level (INFO) can be changed by setting the environment variable MV_LOG_LEVEL. This can help you troubleshoot problems. For example, to get a more detailed log, TRACE level can be used:

Linux

export MV_LOG_LEVEL=TRACE


Windows

set MV_LOG_LEVEL=TRACE