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1、 American Society for Photogrammetry unsigned short wKeyRevision; unsigned short wMinorRevision; unsigned short wNumberOfKeys; struct sKeyEntry unsigned short wKeyID; unsigned short wTIFFTagLocation; unsigned short wCount; unsigned short wValue_Offset; pKey1; ; Where: wKeyDirectoryVersion = 1; / Alw
2、ays wKeyRevision = 1; / Always wMinorRevision = 0; / Always wNumberOfKeys / Number of sets of 4 unsigned shorts to follow Table 23: GeoKey Four Unsigned Shorts Name Definition wKeyID Defined key ID for each piece of GeoTIFF data. IDs contained in the GeoTIFF specification. wTIFFTagLocation Indicates
3、 where the data for this key is located: 0 means data is in the wValue_Offset field as an unsigned short. 34736 means the data is located at index wValue_Offset of the GeoDoubleParamsTag record. 34737 means the data is located at index wValue_Offset of the GeoAsciiParamsTag record. wCount Number of
4、characters in string for values of GeoAsciiParamsTag , otherwise is 1 wValue_Offset Contents vary depending on value for wTIFFTagLocation above GeoDoubleParamsTag Record: (optional) User ID: LASF_Projection Record ID: 34736 This record is simply an array of doubles that contain values referenced by
5、tag sets in the GeoKeyDirectoryTag record. GeoAsciiParamsTag Record: (optional) User ID: LASF_Projection Record ID: 34737 American Society for Photogrammetry char Description15; ; TEXT AREA DESCRIPTION: (optional) User ID: LASF_Spec Record ID: 3 This VLR/EVLR is used for providing a textual descript
6、ion of the content of the LAS file. It is a null terminated, free-form ASCII string. EXTRA BYTES: (optional) User ID: LASF_Spec Record ID: 4 Record Length after Header: n records x 192 bytes The Extra Bytes VLR provides a mechanism whereby additional information can be added to the end of a standard
7、 Point Record. This VLR has been added to LAS 1.4 to formalize a process that has been used in prior versions of LAS. It is envisioned that software that is not cognizant of the meaning of the extra bytes will simply copy these bytes when manipulating files. This record is only needed for LAS files
8、where points contain user-defined “extra bytes”. This happens when the point record size is set to a larger value than required by the point type. For example, when a LAS file that contains point type 1 has a point record size of 32 instead of 28 there are 4 “extra bytes”. The Extra Bytes VLR contai
9、ns a simple description of the type and the meaning of these “extra bytes” so they can be accessed in a consistent manner across applications. The 4 “extra bytes” could, for example, be of data_type 9 - a floating point value - that specifies an “echo width“ for each return. In this case there would
10、 be one EXTRA_BYTES struct in the payload of this VLR. An example with two EXTRA_BYTES struct in the payload are 14 “extra bytes“ that have data type 29 - a floating point vector of length 3 - followed by data type 3 - an unsigned short - that specify the “laser pulse direction“ and a “normalized re
11、flectivity“. The “extra bytes“ are made accessible via a unique name. The “name“ field distinguishes the additional point attributes that a LIDAR software may add to the points in a LAS file so they can be accessed later in a consistent manner by another software. Descriptive names such as “normaliz
12、ed reflectivity“, “echo width“, or “shading normal“ are encouraged. The use of generic names such as “variable1“ or “temp1“ is discouraged. American Society for Photogrammetry / 2 bytes unsigned char data_type; / 1 byte unsigned char options; / 1 byte char name32; / 32 bytes unsigned char unused4; /
13、 4 bytes anytype no_data3; / 24 = 3*8 bytes anytype min3; / 24 = 3*8 bytes anytype max3; / 24 = 3*8 bytes double scale3; / 24 = 3*8 bytes double offset3; / 24 = 3*8 bytes char description32; / 32 bytes ; / total of 192 bytes The “reserved” field and the “unused“ field must be set to zero. Any unused
14、 “no_data“, “min“, “max“, “scale“, or “offset“ fields must be set to zero. Any unused characters in the “name“ or “description“ fields must be set to zero. Table 24: Values for “data_type” Field Value Meaning Size 0 undocumented extra bytes specified by value in “options” field 1 unsigned char 1 byt
15、e 2 Char 1 byte 3 unsigned short 2 bytes 4 Short 2 bytes 5 unsigned long 4 bytes 6 Long 4 bytes 7 unsigned long long 8 bytes 8 long long 8 bytes 9 Float 4 bytes 10 Double 8 bytes 11 unsigned char2 2 byte 12 char2 2 byte 13 unsigned short2 4 bytes 14 short2 4 bytes 15 unsigned long2 8 bytes 16 long2
16、8 bytes 17 unsigned long long216 bytes 18 long long2 16 bytes 19 float2 8 bytes 20 double2 16 bytes 21 unsigned char3 3 byte American Society for Photogrammetry 2) table of new point classifications (PDRF 6-10); and 3) table of new attributes to be stored using Extra Bytes VLRs (must contain fields for units, data type, name, no data, scale, and description). LAS Domain Profile Descriptions reviewed a
