Retrieving Data Chunks - Basler acA2040-55 User Manual

Features

7.23.5 Retrieving Data Chunks

When Chunk Enable and Chunk Mode Active are enabled, the selected data chunks are appended
to each acquired image when the image is transferred to the host computer (see Section 7.23.3 on
page 339), creating a set of chunks. The set of chunks must be parsed to retrieve the chunk data
via a GenICam node map (see below).
The set of chunks includes chunk 1 with the image data ("image data payload") and related
supplementary data (chunk ID and length of the image data payload), followed by the selected data
chunks, each one consisting of the chunk payload and supplementary data.
The PayloadSize parameter value for the device (i.e. for the camera) indicates the calculated
maximum size ("maximum buffer size") that can be expected to occur for a set of chunks. The
calculated maximum size is derived from the current camera parameter settings (ROI size, pixel
format, selected data chunks, etc.).
Make sure all camera parameters are set as desired before reading the
PayloadSize parameter value.
The actual size of a set of chunks as received by the computer ("grab result") can be read form the
PayloadSize value for the grab result. The actual size will be equal to or smaller than the
calculated maximum size.
A set of chunks (chunks one through N) is illustrated in
CRC Checksum chunk was enabled.
Chunk
1
(Image data payload)
Length
Chunk 1
Fig. 117: Example of a Set of Chunks Related to One Image Acquisition
348
Chunk Chunk Chunk
1 1 2
(ID) (Payload)
(Length)
32 bit Length
32 bit
Actual payload size of the grab result
Figure 117. The example assumes that the
Chunk
Chunk Chunk
2
2
...
(ID) (Length)
CRC
Length
32 bit 32 bit
Chunk 2
AW00123409000
Chunk Chunk
N
N
N
(ID) (Length)
32 bit
32 bit
Chunk N
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