Package org.apache.sis.internal.referencing.provider

Class NADCON.Loader

java.lang.Object

org.apache.sis.internal.referencing.provider.DatumShiftGridLoader

org.apache.sis.internal.referencing.provider.NADCON.Loader

Enclosing class:

NADCON

private static final class NADCON.Loader
extends DatumShiftGridLoader

Loaders of NADCON data. Instances of this class exist only at loading time. This class can read both binary and ASCII grid files.

Binary format

NADCON binary files ("*.las" and "*.los") are organized into records with the first record containing the header information, followed by the shift data. The length of each record (including header) depends on the number of columns.

Records are ordered from South to North. Each record (except the header) is an entire row of grid points, with values ordered from West to East. Each value is a float encoded in little endian byte order. Each record ends with a 4 byte separator.

Record data use a different convention than the record header. The header uses degrees of angle with positive values East. But the offset values after the header are in seconds of angle with positive values West. The DatumShiftGrid returned by this loader uses the header convention, which also matches the order in which offset values appear in each row.

Since:

0.7

Version:

0.7

Field Summary

Fields

Modifier and Type	Field	Description
private final StringBuilder	ascii	Temporary buffer for ASCII characters, or null if the file is a binary file.
private static final int	DESCRIPTION_LENGTH	The length of the description in the header, in bytes.
(package private) DatumShiftGridFile.Float<javax.measure.quantity.Angle,javax.measure.quantity.Angle>	grid	The grid created by readGrid(FloatBuffer, Loader, Path).
private static final String	NADCON	The first bytes that we expect to find the header (both binary and ASCII files).
private final int	nx	Number of longitude (nx) and latitude (ny) values.
private final int	ny	Number of longitude (nx) and latitude (ny) values.
private final int	nz	Number of longitude (nx) and latitude (ny) values.
private final float	x0	Longitude and latitude of of the first value in the first record, in degrees.
private final float	y0	Longitude and latitude of of the first value in the first record, in degrees.
private final float	Δx	The difference between longitude (Δx) and latitude (Δy) cells, in degrees.
private final float	Δy	The difference between longitude (Δx) and latitude (Δy) cells, in degrees.

Fields inherited from class org.apache.sis.internal.referencing.provider.DatumShiftGridLoader

buffer, DEGREES_TO_SECONDS, file, SECOND_PRECISION

Constructor Summary

Constructors

Constructor	Description
Loader(ReadableByteChannel channel, ByteBuffer buffer, Path file)	Creates a new reader for the given channel.

Method Summary

Modifier and Type	Method	Description
private void	fillBuffer(FloatBuffer fb)	Invoked when the given FloatBuffer buffer is empty.
private static boolean	isASCII(ByteBuffer buffer)	Returns true if all remaining characters in the buffer are US-ASCII characters for real numbers, except the characters on the first line which may be any printable US-ASCII characters.
private String	nextWord()	Returns the next word from an ASCII file.
(package private) final void	readGrid(FloatBuffer fb, NADCON.Loader latitudeShifts, Path longitudeShifts)	Loads latitude or longitude shifts data.
private void	syncView(FloatBuffer fb)	Sets the position and limit of the given FloatBuffer to the same position and limit than the underlying ByteBuffer, converted to units of float data type.
private org.opengis.util.FactoryException	unexpectedFormat()	Returns the exception to thrown in the file does not seems to be a NADCON format.

Methods inherited from class org.apache.sis.internal.referencing.provider.DatumShiftGridLoader

canNotLoad, ensureBufferContains, log, skip, startLoading

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

DESCRIPTION_LENGTH

private static final int DESCRIPTION_LENGTH

The length of the description in the header, in bytes.

• 56 bytes of NADCON's identification: "NADCON EXTRACTED REGION".
• 8 bytes of "PGM" (unknown meaning).

See Also:

• Constant Field Values

NADCON

private static final String NADCON

The first bytes that we expect to find the header (both binary and ASCII files). We use that as the format signature.

See Also:

• Constant Field Values

x0

private final float x0

Longitude and latitude of of the first value in the first record, in degrees.

y0

private final float y0

Longitude and latitude of of the first value in the first record, in degrees.

Δx

private final float Δx

The difference between longitude (Δx) and latitude (Δy) cells, in degrees.

Δy

private final float Δy

The difference between longitude (Δx) and latitude (Δy) cells, in degrees.

nx

private final int nx

Number of longitude (nx) and latitude (ny) values.

ny

private final int ny

Number of longitude (nx) and latitude (ny) values.

nz

private final int nz

Number of longitude (nx) and latitude (ny) values.

ascii

private final StringBuilder ascii

Temporary buffer for ASCII characters, or null if the file is a binary file.

grid

DatumShiftGridFile.Float<javax.measure.quantity.Angle,javax.measure.quantity.Angle> grid

The grid created by readGrid(FloatBuffer, Loader, Path).

Constructor Details

Loader

Loader(ReadableByteChannel channel,
 ByteBuffer buffer,
 Path file)
throws IOException,
org.opengis.util.FactoryException

Creates a new reader for the given channel. The file can be binary or ASCII. This constructor parses the header immediately, but does not read any grid.

Parameters:

channel - where to read data from.

buffer - the buffer to use. That buffer must use little endian byte order and have a capacity divisible by the size of the float type.

file - path to the longitude or latitude difference file. Used for parameter declaration and error reporting.

Throws:

IOException

org.opengis.util.FactoryException

Method Details

isASCII

private static boolean isASCII(ByteBuffer buffer)

Returns true if all remaining characters in the buffer are US-ASCII characters for real numbers, except the characters on the first line which may be any printable US-ASCII characters. If the content is assumed ASCII, then the buffer position is set to the first EOL character.

Returns:

true if the file seems to be an ASCII one.

nextWord

private String nextWord()
                 throws IOException

Returns the next word from an ASCII file. This method is invoked only for parsing ASCII files, in which case the ascii string builder is non-null.

Throws:

IOException

unexpectedFormat

private org.opengis.util.FactoryException unexpectedFormat()

Returns the exception to thrown in the file does not seems to be a NADCON format.

readGrid

final void readGrid(FloatBuffer fb,
 NADCON.Loader latitudeShifts,
 Path longitudeShifts)
             throws IOException,
org.opengis.util.FactoryException,
org.opengis.referencing.operation.NoninvertibleTransformException

Loads latitude or longitude shifts data. This method should be invoked twice:

1. On an instance created for the latitude shifts file with a latitude argument set to null.
2. On an instance created for the longitude shifts file with a latitude argument set to the instance created in the previous step.

The result is stored in the grid field.

Parameters:

fb - a FloatBuffer view over the full DatumShiftGridLoader.buffer range.

latitudeShifts - the previously loaded latitude shifts, or null if not yet loaded.

longitudeShifts - the file for the longitude grid.

Throws:

IOException

org.opengis.util.FactoryException

org.opengis.referencing.operation.NoninvertibleTransformException

fillBuffer

private void fillBuffer(FloatBuffer fb)
                 throws IOException

Invoked when the given FloatBuffer buffer is empty. This method requests one float from the channel, but the channel will usually give us as many data as the buffer can contain.

Throws:

IOException

syncView

private void syncView(FloatBuffer fb)

Sets the position and limit of the given FloatBuffer to the same position and limit than the underlying ByteBuffer, converted to units of float data type.