LFile::ReadGeoKey

#include "ltwrappr.h"

virtual L_INT LFile::ReadGeoKey(uTag, puType, puCount, pData, pLoadOptions)

L_UINT16 uTag;

/* GeoKey to identify the data in the GeoTIFF file */

L_UINT L_FAR *puType;

/* pointer to a variable */

L_UINT L_FAR *puCount;

/* pointer to a variable */

L_VOID L_FAR *pData;

/* pointer to the buffer for the data */

pLOADFILEOPTION pLoadOptions;

/* pointer to optional extended load options */

Gets the specified GeoKey data from a TIFF file. This function is provided to support GeoKeys that you define.

Parameter

Description

uTag

GeoKey ID that you set by calling LFile::SetGeoKey function. Values of the GeoKey ID range between 0 and 65535. Possible ranges are:

 

Range

Meaning

 

0..1023

Do not use; reserved for future use.

 

1024..2047

GeoTIFF configuration keys.

 

2048..3071

Geographic/Geocentric CS Parameter Keys.

 

3072..4095

Projected CS Parameter Keys.

 

4096..5119

Vertical CS Parameter keys.

 

5120..32767

Reserved.

 

32768..65535

Private use – use to store your own data.

puType

Pointer to a variable to be updated with the GeoKey type. This indicates whether the data pointed to by pData is SHORT, DOUBLE or ASCII. Possible values are:

 

Value

Meaning

 

TAG_ASCII

[2] The data pointed to by pData is an array of ASCII bytes.

 

TAG_SHORT

[3] The data pointed to by pData is an array of SHORT values (2 bytes each).

 

TAG_DOUBLE

[12] The data pointed to by pData is an array of floating points in DOUBLE format (8 bytes each).

puCount

Pointer to the variable to be updated with the number of items required for the pData buffer. Note that this is not the required number of bytes. The required number of bytes will be (*puCount) * number of bytes per value (1 for ASCII, 2 for SHORT, 8 for DOUBLE).

If pData passed as NOT NULL, this variable will be updated with the count of data items.

pData

Pointer to the buffer to be updated with the data. You can pass NULL if you want to use this function's return value to determine the required buffer size.

pLoadOptions

Pointer to optional extended load options. Pass NULL to use the default load options.

Returns

SUCCESS

The function was successful.

< 1

An error occurred. Refer to Return Codes.

Comments

Obtains the GeoKey data from a particular file.

It is often convenient to call this function twice, as follows:

1.

Call the function the first time, passing NULL to the pData parameter, and using the return value to determine the required size of the buffer.

2.

Allocate the buffer.

3.

Call the function the second time, passing a pointer to your buffer in the pData parameter.

The most efficient way of reading the GeoKeys in a file is to enumerate them with LFile::EnumGeoKeys and then read each GeoKey with LFile::ReadGeoKey.

For more information about GeoKeys, refer to Implementing GeoKeys (GeoTIFF tags).

Required DLLs and Libraries

LTFIL

LFTIF

For a listing of the exact DLLs and Libraries needed, based on the toolkit version, refer to Files To Be Included With Your Application.

See Also

Functions:

LFile::SetGeoKey, LFile::GetGeoKey, LFile::WriteGeoKey, LFile::WriteMetaData, LFile::EnumGeoKeys, LFile::SaveFile, LFile::SaveBitmap

Topics:

Implementing GeoKeys (GeoTIFF tags)

 

Implementing TIFF Comments and Tags

 

Raster Image Functions: Working with GeoKeys

Example

For an example, refer to LFile::WriteGeoKey function.