NTV2 Reader

Tihs module provides functionality to read and utilize NTV2 grid files for coordinate transformations. It has been adapted from Jaimie Dodd’s ntv2reader.py

Classes

class geodepy.ntv2reader.NTv2Grid(num_orec, num_srec, num_file, gs_type, version, system_f, system_t, major_f, minor_f, major_t, minor_t, file_path)

NTv2 Grid Parameters

Parameters:

• num_orec – Number of header identifiers

• num_srec – Number of sub-header idents

• num_file – Number of subgrids in file

• gs_type – grid shift type

• version – grid file version

• system_f – reference system

• system_t – reference system

• major_f – semi major of from system

• minor_f – semi minor of from system

• major_t – semi major of to system

• minor_t – semi minor of to system

• file_path – full path to ntv2 gsb file

class geodepy.ntv2reader.SubGrid(sub_name, parent, created, updated, s_lat, n_lat, e_long, w_long, lat_inc, long_inc, gs_count)

Sub Grid Parameters

Parameters:

• sub_name – subgrid name

• parent – parent name

• created – date created

• updated – date modified

• s_lat – south latitude extents

• n_lat – north latitude extents

• e_long – east longitude extents

• w_long – west longitude extents

• lat_inc – latitude increment

• long_inc – longitude increment

• gs_count – total nodes in subgrid

ntv2_bicubic(lat, lon, num_cols, row, col, f, start_byte)

Function to perform bicubic interpolation of the four ntv2 fields at a point of interest.

Parameters:

• lat – latitude of the point of interest (arc-seconds)

• lon – longitude of the point of interest (negative arc-seconds)

• num_cols – number of columns in grid

• row – row number of point to the bottom right of the point of interest

• col – column number of point to the bottom right of the point of interest

• f – variable for open file NTv2 being read as binary

• start_byte – start index of subgrid

Returns:

Four field tuple of interpolation results at point of interest.

ntv2_bilinear(lat, lon, num_cols, row, col, f, start_byte)

Function to perform bicubic interpolation of the four ntv2 fields at a point of interest.

Parameters:

• lat – latitude of the point of interest (arc-seconds)

• lon – longitude of the point of interest (negative arc-seconds)

• num_cols – number of columns in grid

• row – row number of point to the bottom right of the point of interest

• col – column number of point to the bottom right of the point of interest

• f – variable for open file NTv2 being read as binary

• start_byte – start index of subgrid

Returns:

Four field tuple of interpolation results at point of interest.

Functions

geodepy.ntv2reader.read_ntv2_file(ntv2_gsb_file)

Function to read an ntv2 gsb file and create grid & subgrid objects

Parameters:

ntv2_gsb_file – full path to ntv2 file

Returns:

Ntv2 grid object

geodepy.ntv2reader.interpolate_ntv2(grid_object, lat, lon, method='bicubic')

Function to interpolate Ntv2Grid objects

Parameters:

• grid_object – Ntv2Grid object

• lat – latitude (decimal degrees)

• lon – longitude (decimal degrees)

• method – interpolation strategy, bicubic or bilinear

Returns:

Tuple of four ntv2 fields

geodepy.ntv2reader.read_node(f)

Function to read in values of nodes

Parameters:

f – variable for open file NTv2 being read as binary

Returns:

Tuple containing the four ntv2 fields at the grid node.

geodepy.ntv2reader.bilinear_interpolation(n1, n2, n3, n4, x, y)

Bilinear interpolation of value for point of interest (P).

Parameters:

• n1 – value at node 1

• n2 – value at node 2

• n3 – value at node 3

• n4 – value at node 4

• x – interpolation scale factor for x axis

• y – interpolation scale factor for y axis

Returns:

Value at node P

geodepy.ntv2reader.bicubic_interpolation(n1, n2, n3, n4, n5, n6, n7, n8, n9, n10, n11, n12, n13, n14, n15, n16, x, y)

Bicubic interpolation of value for point of interest (P).

Parameters:

• n1 – value at node 1

• n2 – value at node 2

• n3 – value at node 3

• n4 – value at node 4

• n5 – value at node 5

• n6 – value at node 6

• n7 – value at node 7

• n8 – value at node 8

• n9 – value at node 9

• n10 – value at node 10

• n11 – value at node 11

• n12 – value at node 12

• n13 – value at node 13

• n14 – value at node 14

• n15 – value at node 16

• n16 – value at node 17

• x – interpolation scale factor for x axis

• y – interpolation scale factor for y axis

Returns:

Value at node P