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Program: GETVAL

Purpose: Get image values at given positions in a set

Category: UTILITY

File: getval.c

Author: M.G.R. Vogelaar

Keywords:

INSET= Give set (,subset):

Maximum number of subsets is 1.
The set/subset can have any dimension.


OUTFILE= Name of output file: [GETVAL_output.txt]

ASCII file on disk which contains the positions in
POSITION= and the corresponding image values. The
image values are formatted according the string
entered in FORMAT=


APPEND= Ok to append? [Y]/N

ASCII file on disk exists. Is it ok to append?


FORMAT= Give format for output: [fffffffff.fffff]

Print numbers on screen or save numbers in file in user
given output format.
See description for possible formats


POSITION= Enter position in (......): [STOP]

Positions are entered as grids or physical coordinates
(or mixed) according to the GIPSY rules for coordinate
input. Each position consists of n numbers where n is the
dimension of INSET=
You can abort the loop by pressing [enter].
If you want to read coordinates from file then this file
must have extension '.rcl' and you can use it in the
following way: POSITION= (where myfile.rcl is the file on disk).
Examples:

POSITION= 10 -24
Pixel position RA=10, DEC=-24

POSITION= * 10 12 8 -24
RA = 10 hours, 12 minutes, 8 seconds,
DEC = pixel -24

POSITION= * 10 12 8 * -67 8 9.6
RA = 10 hours, 12 minutes, 8 seconds,
DEC = -67 degrees, 8 minutes, 9.6 seconds, in a 2-dimensional
area and in the epoch as found in the descriptor of the set.

POSITION= *2000.0 3 14 38.02 *2000.0 41 13 54.84
Input of RA 3 h 14 m 38.02 s, DEC 41 d 13 m 54.84 s in
epoch 2000.0

You can also use the prefixes 'G' and 'E':

G Galactic longitude or latitude in degrees
E Ecliptic longitude or latitude in degrees



Description: Program GETVAL gets image values from INSET= at user
given positions in POSITION=
The position keyword is asked in a loop. Coordinates
within the frame of the set and with an image value
that is not blank, are plotted on screen and saved to disk
in file OUTFILE= together with the image value. The
image value is formatted according to the string in FORMAT=
Example output from RA, DEC positions in a set:

RA DEC IMAGEVALUE
===================================
0.000000 0.000000 9854.73340
1.000000 1.000000 10071.29688
3.000000 3.000000 7277.25098
3.000000 3.000000 7277.25098
-2.000000 -2.000000 7707.51221

Note: The header is not part of the output.
Note: Positions that correspond to a blank image value
are not saved to file. However a message appears
in the GIPSY LOG file.


The program is written for people who want to know image
values in a set on certain positions without using
interpolation (as for instance in program TRACE).
GETVAL is different from PRINT because is works on
arbitrary positions and not on boxes and its output
is directed to an ASCII file on disk. Also GETVAL
differs from GDS2TEXT because the latter works on a
box only.


FORMATS
=======


The specification in FORMAT= is called a 'format image'.
A 'format image' is used to print numbers in a user given
format consisting of characters representing the
wanted output format. The syntax is:

flag(s) Zero or more flags, in any order, which modify the
meaning of the conversion specification. The flag
characters and their meanings are:

- The result of the conversion is left-
justified within the field.

+ The result of a signed conversion always
begins with a sign, "+" or "-".

string Characters, some with special meaning.
If the string (f.i. FFFFF.FF or gggg.gg or wwwww)
contains no dot, the number of characters specify
a minimum field width. For an output field, if the
converted value has fewer characters than the field
width, it is padded on the left (or right, if the
left-adjustment flag, - has been given) to the field
width.
If the string contains a dot, the total number of
characters including the dot is the minimum field width
and the number of characters after the dot is the
precision.

The characters are used to determine the conversion
type. If the string contains an:

'e' or 'E'
The floating-point-number argument is
printed in the style [-]drddde+dd,
where there is one digit before the
radix character, and the number of
digits after it is equal to the
precision. The E conversion character
produces a number with E introducing
the exponent instead of e. The
exponent always contains at least two
digits. However, if the value to be
printed requires an exponent greater
than two digits, additional exponent
digits are printed as necessary.

'g' or 'G'

The floating-point-number argument is
printed in style f or e (or int style E
n the case of a G conversion
character), with the precision
specifying the number of significant
digits. The style used depends on the
value converted; style e is used only
if the exponent resulting from the
conversion is less than -4 or greater
than or equal to the precision.

others
Strings without 'e', 'E', 'g' and 'G'
indicate a floating point conversion.
The floating point number argument is
printed in decimal notation in the
style [-]dddrddd, where the number of
digits after the radix character, r, is
equal to the precision specification.

If the result of a conversion is longer than the
field width, an asterisk is returned. If the
input number is a blank, a 'b' is returned.



Examples: Format string: +eeeeee.eeee
Number: 43345.5436
Result: +4.3346e+04
Remark: exponential format
signed conversion
field width: 12
precision: 4

Format string: gggg.ggggg
Number: 34.43
Result: 34.430
Remark: Field width is 10
Number of significant digits is 5

Format string: +ffff.ff
Number: 23.456
Result: +23.46
Remark: signed conversion

Format string: -ffff
Number: 345.87
Result: 346
Remark: left justified

Format string: -+ffff.fff
Number: 34.43
Result: +34.430
Remark: left justified
signed conversion

Format string: eee.eeee
Number: 234.43
Result: *
Remark: Field width too small
for conversion

Format string: ffff.ff
Number: blank
Result: b
Remark: input was a blank




Notes:

Example: See above.

Updates: Apr 23, 1998: VOG, Document created.