Re: [Elphel-support] 答复: 答复: sync stereo with lidar

[Oleg]

Hello,

Did you mean this question?

> We have Garmin GPS 18x 5Hz GPS receiver bought from you. How should we
> connect GPS to stereo camera? Shall we have a 103696 board? But I can not
> find how to connect it to 10393 camera on 103696 introduction page (-
> https://wiki.elphel.com/wiki/103696).


For 10393 you should have 10389 board (https://wiki.elphel.com/wiki/10389)

Garmin GPS 18x 5Hz GPS - is it serial? or usb?
If usb then use a eSATA+USB port or micro usb port
If serial then you need to have 103696 - 103696 is connected to J8 or J9
ports of 10389 with 10-contact flat cable.

Best regards,
Oleg Dzhimiev
Electronics Engineer
phone: +1 801 783  x124
Elphel, Inc.
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[Elphel-support] 答复: 答复: sync stereo with lidar

[Tao Zhang]

Hi Andrey and Oleg,
Would you please help answer questions in the last email?
Thank.

Tao Zhang
章   涛

发件人: Tao Zhang
发送时间: 2018年5月7日 16:12
收件人: 'Andrey Filippov' 
抄送: Elphel Support ; Elphel Sales | Olga 
Filippova ; Winston Zhang ; 
Qun Gu ; Pioneer Li 
主题: 答复: 答复: [Elphel-support] sync stereo with lidar

Hi Andrey,
We have Garmin GPS 18x 5Hz GPS receiver bought from you. How should we connect 
GPS to stereo camera? Shall we have a 103696 board? But I can not find how to 
connect it to 10393 camera on 103696 introduction page 
(-https://wiki.elphel.com/wiki/103696).

Tao Zhang
章   涛

发件人: Andrey Filippov >
发送时间: 2018年2月1日 13:49
收件人: Tao Zhang 
>
抄送: Elphel Support 
>; 
Elphel Sales | Olga Filippova >; 
Winston Zhang 
>; 
Qun Gu >; Pioneer Li 
>
主题: Re: 答复: [Elphel-support] sync stereo with lidar

Tao,

USB GPS does not have 1pps signal (only serial has), precise synchronization is 
not possible that way. GPS time is available in each frame Exif header data - 
recorded on internal SSD or sent over the network.

The high resolution time stamps (1 microsecond step) are also provided with 
each  image, but they use internal camera clock, not the GPS.

This is why for precise synchronization you need to use event logger- it 
records events and timestamps them using the same clock.

If you had serial GPS with https://wiki.elphel.com/wiki/103696 - you would 
still need to use event logger - with serial GPS there will be 1 PPS precise 
GPS events timestamped with camera internal clock, and the images timestamped 
wit the same clock - that provides absolute calibration for the camera internal 
clock.

Without serial GPS you may use pulses from the LIDAR (it is possible to provide 
LIDAR pulse number over the Ethernet in addition to the precise time over the 
sync cable)

Andrey

 On Wed, 31 Jan 2018 18:12:00 -0800 Tao 
Zhang> wrote 

Hi Andrey,
We prefer to use GPS to synchronize stereo with lidar.
Where do those images that contain timestamp store in internal disk? Can we get 
it from ethernet continuously?

Tao Zhang
章   涛

发件人: Andrey Filippov [mailto:and...@elphel.com]
发送时间: 2018年2月1日 1:52
收件人: Tao Zhang 
>
抄送: Elphel Support 
>; 
Elphel Sales | Olga Filippova >; 
Winston Zhang 
>; 
Qun Gu >; Pioneer Li 
>
主题: Re: [Elphel-support] sync stereo with lidar

Hi Tao,

There are several ways how to do that:
One method would be be to get camera sync pulses for each frame and use 
external electronics to match with the LIDAR.
Another is to provide pulses from the LIDAR to the camera and record them with 
in-camera FPGA logger (https://wiki.elphel.com/wiki/Event_logger), together 
with the camera frames. In this case the camera will record 2 types of events:
 -  image frames with the frame number, frame timestamp that will be recorded 
in each frame header as Exif.
 - external pulse
Each of the two types of events will have a logger timestamp (with microsecond 
resolution). Logger can also record GPS timestamps (for serial GPS only and 
103696 board -https://wiki.elphel.com/wiki/103696) and IMU 
(https://wiki.elphel.com/wiki/103695), in your case there are just 2 types 
listed above.

Both output (+5V pulses) and input (3.3V..5.0V) are available through the 2.5mm 
audio connector (marked "sync" 
https://wiki.elphel.com/images/0/0f/NC393-CS_marked_ports.jpeg ), here is the 
pinout and description: https://wiki.elphel.com/wiki/103891 .

Andrey

 On Wed, 31 Jan 2018 04:19:04 -0800 Tao 
Zhang> wrote 

Hi Andrey,
We are going to use stereo with lidar. We need to sync stereo frames with lidar 
point cloud. Do you have any suggestions on how to do that?
Thanks.

Tao Zhang
章   涛

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