Binary Formats
In order to preserve some compactness in dump files and network transmissions, the binary formats need to retain their native compression. All binary formats are hex-encoded before output.
The point and patch binary formats start with a common header, which provides:
endianness flag, to allow portability between architectures
pcid number, to look up the schema information in the
pointcloud_formats
table
The patch binary formats have additional standard header information:
the compression number, which indicates how to interpret the data
the number of points in the patch
Point Binary
byte: endianness (1 = NDR, 0 = XDR)
uint32: pcid (key to POINTCLOUD_SCHEMAS)
uchar[]: pointdata (interpret relative to pcid)
Patch Binary
Uncompressed
byte: endianness (1 = NDR, 0 = XDR)
uint32: pcid (key to POINTCLOUD_SCHEMAS)
uint32: 0 = no compression
uint32: npoints
pointdata[]: interpret relative to pcid
Dimensional
byte: endianness (1 = NDR, 0 = XDR)
uint32: pcid (key to POINTCLOUD_SCHEMAS)
uint32: 2 = dimensional compression
uint32: npoints
dimensions[]: dimensionally compressed data for each dimension
Each compressed dimension starts with a byte, that gives the compression type, and then a uint32 that gives the size of the segment in bytes.
byte: dimensional compression type (0-3)
uint32: size of the compressed dimension in bytes
data[]: the compressed dimensional values
There are four possible compression types used in dimensional compression:
no compression = 0,
run-length compression = 1,
significant bits removal = 2,
deflate = 3
No dimension compress
For dimensional compression 0 (no compression) the values just appear in order. The length of words in this dimension must be determined from the schema document.
word[]:
Run-length compress dimension
For run-length compression, the data stream consists of a set of pairs: a byte value indicating the length of the run, and a data value indicating the value that is repeated.
byte: number of times the word repeats
word: value of the word being repeated
.... repeated for the number of runs
The length of words in this dimension must be determined from the schema document.
Significant bits removal on dimension
Significant bits removal starts with two words. The first word just gives the number of bits that are “significant”, that is the number of bits left after the common bits are removed from any given word. The second word is a bitmask of the common bits, with the final, variable bits zeroed out.
word1: number of variable bits in this dimension
word2: the bits that are shared by every word in this dimension
data[]: variable bits packed into a data buffer
Deflate dimension
Where simple compression schemes fail, general purpose compression is applied to the dimension using zlib. The data area is a raw zlib buffer suitable for passing directly to the inflate() function. The size of the input buffer is given in the common dimension header. The size of the output buffer can be derived from the patch metadata by multiplying the dimension word size by the number of points in the patch.
LAZ
byte: endianness (1 = NDR, 0 = XDR)
uint32: pcid (key to POINTCLOUD_SCHEMAS)
uint32: 2 = LAZ compression
uint32: npoints
uint32: LAZ data size
data[]: LAZ data
Use laz-perf library to read the LAZ data buffer out into a LAZ buffer.