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Copyright (c) 2009-2013 RoboPeak Team
Copyright (c) 2013-2019 Shanghai Slamtec Co., Ltd.
Figure 4-23 The Abstract Description for the Response Data Packet of Express
Scan Request
The above figure indicates the data response packet format of RPLIDAR in the
express scan mode. For convenience, after RPLIDAR receives the express scan
request and enter express scan mode, the first sent data response packet is denoted
as 𝑃
ο„΅
, the second 𝑃
ο„Ά
and the i
th
𝑃
ο‡œ
. Accordingly, πœ”
𝑖
indicates the actual angular physical
quantity corresponded with the start_angle_q6 field of 𝑃
𝑖
Since in express scan mode, the corresponding data of measurement sampling is
stored respectively and sequentially in the Cabin of each data response packet. In
every 𝑃
ο‡œ
response data, the data of the k
th
measurement sampling point is denoted
as 𝐢
ο‡ž
. It carries the distance value π·π‘–π‘ π‘‘π‘Žπ‘›π‘π‘’
ο‡ž
and the included angle compensation
π‘‘πœƒ
ο‡ž
corresponded with the current measurement sampling point.
The actual included angle πœƒ
ο‡ž
of any measurement sampling point 𝐢
ο‡ž
can be
calculated out via the following formula:
πœƒ
ο‡ž
= πœ”
ο‡œ
+
𝐴𝑛𝑔𝑙𝑒𝐷𝑖𝑓𝑓(πœ”
ο‡œ
,πœ”
ο‡œο„Ύο„΅
)
32
β‹… π‘˜ βˆ’ π‘‘πœƒ
ο‡ž
The function 𝐴𝑛𝑔𝑙𝑒𝐷𝑖𝑓𝑓(πœ”
ο‡œ
,πœ”
ο‡œο„Ύο„΅
) in the above formula is defined as below:
AngleDiff
(
πœ”
ο‡œ
,πœ”
ο‡œο„Ύο„΅
)
=

πœ”
ο‡œο„Ύο„΅
βˆ’ πœ”
ο‡œ
, πœ”
ο‡œ
≀ πœ”
ο‡œο„Ύο„΅
360 + πœ”
ο‡œο„Ύο„΅
βˆ’ πœ”
ο‡œ
, πœ”
ο‡œ
> πœ”
ο‡œο„Ύο„΅
Data Processing of the Express Scan Data (Ultra Capsuled Express Scans)
Measurements are grouped to 3 samples per set, and stored in 32bit ultra cabins.
Each ultra cabin consists of one sample and two predicts. The angle offset fields are
removed in this data format. The SDK calculates angle offsets by LIDARs’ optical
model and start_angle_q6 field of the response packet.
The data process and calculation is complicated. As a result, using SDK to deal with
ultra capsuled packets is strongly recommended. You may refer to the source code
of RPLIDAR public SDK in case you need to understand its algorithm and principles
or to parse ultra capsuled packets.