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Old 08-21-2017, 11:45 AM   #1
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CLI Program to do math transformation on a set of x,y coordinates

Hi all
I'm looking for a cli program that does traslations, rotations, stretches, ecc, given a list of 2D coordinates

E.g., given a file with the list of coords ( a square, in this case )

Ii need something that does
PROGRAM -i inputfile --traslate +4x,-2y --rotate 40deg ... and so on

"R" is a bit overkill


Old 08-21-2017, 02:03 PM   #2
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expr is a built-in utility that lets you evaluate mathematical, logical, and scientific expressions, and nearly anything else. Its most commonly used in shell scripts though. The expr manpage isn't particularly helpful, so you'll need to search the internet to get help with it..

Last edited by justmy2cents; 08-22-2017 at 01:05 PM.
Old 08-21-2017, 02:27 PM   #3
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Belated welcome to LQ!

Please place your code snippets inside [CODE]...[/CODE] tags for better readability. You may type those yourself or click the "#" button in the edit controls.

From the description you are doing simple coordinate transformations. The operations reduce to specifying the transformation function, the relationship between original and new coordinates, and should be mostly language agnostic.

An obvious candidate would be GNU bc. Simply write the mathematical transformation function(s) in bc's syntax, then pass it your original coordinates.

If you could work better with matrix notation or need a more complete solution, GNU Octave would be my tool of choice.

If you are up to some simple programming beyond the math itself, just choose a language you are familiar with and get started. The transformations you describe should not need anything beyond the built-in math capabilities of most programming languages. If you do need more complex functions, check available libs.

One caution with shell scripts though (thinking specifically about Bash), it supports only integer math operations natively. So if you need floating point precision you will need to invoke an external program, usually bc for me.

And yet another caution using expr as it has been already mentioned. From O'Reilly, Classic Shell Scripting:

# Classic Shell Scripting - Oreilly, Section 7.6.3
# The expr command is one of the few Unix commands that is poorly designed and hard to use.
# Although standardized by POSIX, its use in new programs is strongly discouraged, since
# there are other programs and facilities that do a better job. In shell scripting, the major
# use of expr is for shell arithmetic, so that is what we focus on here. Read the expr(1)
# manpage if you're curious about the rest of what it can do.
# expr's syntax is picky: operands and operators must each be separate command-line arguments;
# thus liberal use of whitespace is highly recommended. Many of expr's operators are also
# shell metacharacters, so careful quoting is also required.
Use the shell built-ins instead!
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Old 08-22-2017, 04:19 AM   #4
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I was actually looking for an already cooked pork chop but actually bc and some bash glue is enough to manage few thousands of records

Old 08-22-2017, 05:28 PM   #5
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I'd also suggest python with numpy.
You could then combine this with argparse to make it a cli tool if needed.

import numpy as np

def transform(array, x=0, y=0):
    '''In place transformation of x, y coordinates'''
    array[:, 0] += x
    array[:, 1] += y 

my_array = np.loadtxt('coord', delimiter=',', dtype='intc')
array([[3, 2],
       [5, 2],
       [5, 5],
       [3, 5]], dtype=int32)
transform(my_array, x=-10)
array([[-7,  2],
       [-5,  2],
       [-5,  5],
       [-7,  5]], dtype=int32)
Old 08-22-2017, 06:02 PM   #6
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You can do math in bash, but it doesn't do floating point. Although shift the decimal a few places and that doesn't matter much.

$ echo $(( $(( 10 * 6 )) / 3 ))

You could use bc to do more complex math with floating point natively. Mostly I fake shift the decimal and do bash math.

Like a couple $1.65 items with a quantity of 6 after an 8.5% tax.

$ FAKETAX=$(( 1000 + 85 )); FAKEQUANTITY=6; FAKEVALUE=$((100 + 65)); \
  FAKEFLOAT=$( echo $(( $(( $FAKETAX * $(( $FAKEQUANTITY * $FAKEVALUE )) )) / 1000 )) ); \
  echo -n $(( $FAKEFLOAT / 100 )); echo -n "."; echo ${FAKEFLOAT:$FAKEOFFSET:2}
A bit of a hacky way to do math, but if you don't feel like mixing your poisons, an option.
Old 08-22-2017, 06:48 PM   #7
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Rotation need sin() and cos() functions.



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