Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.atnf.csiro.au/computing/software/gipsy/tsk/regrid.dc1 Дата изменения: Mon Nov 30 19:20:53 1998 Дата индексирования: Fri Jan 16 01:13:23 2009 Кодировка:

Program: REGRID

Purpose: Create an output map with different grid along one axis.

Category: COORDINATES, MANIPULATION, UTILITY

File: regrid.c

Author: M.G.R. Vogelaar

Keywords:

INSET= Give NAME of set:

There is no need to specify subsets. The 'regrid axis'
is entered with AXNAME=


AXNAME= Enter name of axis to regrid: [Abort]

After INSET= a list is displayed with the names of
all axes in INSET=. One of these axes can be selected
to become the 'regrid axis'. For this axis you will
be prompted to enter a new grid spacing. Abbreviation
of axis names is allowed.


CDELT= Enter new grid spac. for ... axis in ...: [header]

The new grid spacing sets the regridding. It can be a
number greater than or less than the original value.
Its sign will be converted to the sign of the
original grid spacing. In the prompt the axis name
and the corresponding units are listed. The default
spacing is read from the header. The units are also
read from the header, but if these units are DEGREE,
then they are converted to seconds of arc.


BOX= Give BOX in .... [entire subset]

Resize the INPUT by entering a box. The default is
the entire set as selected by INSET= and the box
values cannot exceed the limits of INSET=
Note that the output set will show axis limits as in
BOX= except for the 'regrid axis' which will get
new values because of the regridding.


OUTSET= Give output set:

This will be the name of the regridded INSET=
It has sizes as defined by BOX= The size of the
regridded axis is also defined by CDELT=


IPOL= Enter interpolation method: [1=linear]

See also 'description'.
A list with interpolation methods will be presented.
After selecting a method, the program starts to regrid.


WIDTH= Enter width of regridding function: [1.0]

Only asked if IPOL=2.
Give the position of the first zero of the sinc
in old gridunits.




Description: Regrid data in INSET= in one direction. The direction
is one of the axis names in a set. Before the prompt
AXNAME= you get a list with all set axes. The regrid
direction is selected by entering one of the axis names.
If you want to regrid more than one axis, please repeat
the process onto intermediate results (sets).
The sign of the grid spacing cannot be altered. If you
want to change this sign then use a program like AXSWAP
to do this. The new limits of the 'regrid axis' LO and
HI are:

LOnew = LOold * ABS(CDELTold/CDELTnew)
HInew = HIold * ABS(CDELTold/CDELTnew)



INTERPOLATIONS:
==============


1) Linear interpolation

Standard linear interpolation between two pixels in the
input image.


2) Sinc interpolation

Interpolation method is SINC.
This gives a weight to an old pixel dependent on
its distance to the new pixel position and on
the ratio of old and new gridspacings.
The default regridding function is the following:

sin pi*x pi 2
R(x) = -------- exp ( 4*ln(--) * x )
pi*x 4

with a = signed distance from the central pixel
in x or y. This regridding function has the
following properties:
R(0) = 1; R(+/-0.5) = 0.5; R(+/-1) = 0


3) Spline interpolation

Standard 1-dim. cubic spline interpolation.

4) Average

Replace output by average of a number of input pixels.
This number of input pixels is set by the ratio of
input pixels to output pixels. The averaging will only
work if this ratio is integer and greater than 1.



BLANKS:
======

All interpolation methods take care of blank image data.
1) If the LINEAR interpolation is used, all input values
that are blank, set the corresponding output values
to blank.
2) If the SINC method is used, then the weight of an
'input' blank is set to 0. If the sum of the weights
is 0 then a blank is returned for the output.
3) The SPLINE method interpolates over blanks.



Notes: .......

Example: .......

Updates: Dec 07, 1995: VOG, Document created.
Nov 30, 1998: VOG, Average option inserted.