Which regular expression to use to convert this string to an array?

Question

From a geospatial column in mysql I'm getting the following string-value which I want to convert into an array. Ultimate goal is to convert it to geoJSON.

POLYGON((4.885838 52.388063,4.891061 52.388381,4.890973 52.382909))

This string has 3 coordinate pairs with the x and y coordinate separated by a space and the pairs separated with a comma. The exact number is not known and variable. Also the POLYGON can differ to three different settings.

With my little knowledge of reg. expressions I came up with this:

$pat = '/^(POLYGON|LINESTRING|POINT)(\(\() (.....) (\)\))$/';
preg_match($pat, $str, $matches);

With the part of the coordinates with the double brackets as an uncertain part.

Could anyone help me with this?

edit Ultimately the resulting array should look like this:

$array['type'] = POLYGON | LINESTRING ....
$array['coordinates'] = array of all the coordinates.

Added an example result array. Thank you for looking into it! — stUrb
– stUrb, Commented May 14, 2012 at 8:43

Li-aung Yip · Accepted Answer · 2012-05-14 09:05:15Z

2

You're best off tackling this in stages. Only the first stage needs to use regex:

Find the entire string of coordinates as one glob, for example:

"4.885838 52.388063,4.891061 52.388381,4.890973 52.382909"
Split that string up into coordinate pairs separated by comma. In Python, we would use str.split(','). I believe your PHP equivalent is called explode().

[ "4.885838 52.388063" , "4.891061 52.388381" , "4.890973 52.382909" ]
Split each coordinate pair into two numbers separated by space: str.split(' ').

[ ["4.885838","52.388063"] , ["4.891061","52.388381"] , ["4.890973","52.382909"] ]
Convert to floats. In python we use float(): your local equivalent might be called str2float() or similar.

[ [4.885838,52.388063] , [4.891061,52.388381] , [4.890973,52.382909] ]

To find the string of numbers for step 1, try the regex

([-]?\d+.\d+ [-]?\d+.\d+)((,[-]?\d+.\d+ [-]?\d+.\d+)+)?

which finds at least one pair of coordinates in x y format, with coordinate pairs separated by commas. You can see the regular expression in action on regexr.

edited May 14, 2012 at 9:05

answered May 14, 2012 at 8:44

Li-aung Yip

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1 Comment

stUrb Over a year ago

Thank you for your answer. I used the method you described but the function of emil Vikström.

Emil Vikström · Accepted Answer · 2012-05-14 08:42:12Z

0

I think it's easier and more maintainable to just use explode and array_map on the coordinate string:

$coordString = $matches[3];
$coordinates = array_map(function($e) { return explode(' ', $e); },
                         explode(',', $coordString));

answered May 14, 2012 at 8:42

Emil Vikström

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Milko · Accepted Answer · 2020-04-07 13:37:05Z

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I have stumbled into the same problem, however in my case I found patterns such as POLYGON ((-1.23 2.34, 3.45 4.56), (3.21 4.32, 5.43 6.54)) and the above regular expression did not work for me to perform step 1. After some head scratching I came with the following pattern: /(((([-]?\d+\.\d+) ([-]?\d+\.\d+))[, ]?)+[, ]?)+/. You would then iterate over the matches splitting on the commas and finally split on the spaces. I am not a regex guru, so maybe someone has a better solution.

answered Apr 7, 2020 at 13:37

Milko

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