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

2018-01-31 Thread Andrey Filippov 
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 
Zhangtao.zh...@blacksesame.com.cn 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 tao.zh...@blacksesame.com.cn
 抄送: Elphel Support support-list@support.elphel.com; Elphel Sales | 
Olga Filippova sa...@elphel.com; Winston Zhang 
winston.zh...@blacksesame.com.cn; Qun Gu 
qun...@blacksesame.com; Pioneer Li pioneer...@blacksesame.com.cn
 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 
Zhangtao.zh...@blacksesame.com.cn 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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[Elphel-support] 答复: sync stereo with lidar

2018-01-31 Thread Tao Zhang 
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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