Obtain double precision values from inconsitent strings for using ST_GeomFromText (PostGIS)

问题

I have a PostgreSQL table with a column containing strings in the following format:

    '3.985 58.934, 4.56 61.2323, 5.4 63.234355, 3.25982 59.309' 
    '3.985 58.934, 4.56 61.2323, 5.4 63.234355, 3.25982 59.309, 4.5632 58.32423'
    'and so on...'

As you can see the column contains coordinates in different lengths as strings in one line. I would like to use the PostGIS function:

    ST_GeomFromText('LINESTRING(3.985 58.934, 4.56 61.2323, 5.4 63.234355, 3.25982 
    59.309)', 4326)

The following questions now appears:

The PostGIS functions requires double precision values in the right format as shown above. How can I generate double precision values from strings when I don't know how long the strings will be and how many characters each coordinate has?

Thanks for your help in advance!

Jann

回答1:

According to the docs, ST_GeomFromText requires (text, integer), not (double precision).

All you need to do is CONCAT() and it should work.

Solution

ST_GeomFromText(CONCAT('LINESTRING(', "YourTable"."YourString", ')'), 4326);

For your testing

SELECT
    ST_GeomFromText('LINESTRING(3.985 58.934, 4.56 61.2323, 5.4 63.234355, 3.25982 59.309)', 4326),
    CONCAT('LINESTRING(', "T1"."C1", ')'),
    ST_GeomFromText(CONCAT('LINESTRING(', "T1"."C1", ')'), 4326)
FROM
    (
        SELECT '3.985 58.934, 4.56 61.2323, 5.4 63.234355, 3.25982 59.309, 4.5632 58.32423' AS "C1"
    ) AS "T1";

Just for fun

I decided to convert your string into the originally requested DOUBLE PRECISION and then back into a string... the end result is the same as above, but it does it with a lot more work. Nevertheless, it is what you asked for.

SELECT
    ST_GeomFromText(CONCAT('LINESTRING(', (SELECT STRING_AGG(ARRAY_TO_STRING("Line"."Points", ' '), ',') FROM REGEXP_MATCHES(ARRAY_TO_STRING(REGEXP_SPLIT_TO_ARRAY("T1"."C1", E', | ')::DOUBLE PRECISION[], ' '), '(\d*\.\d*) (\d*\.\d*)', 'g') AS "Line"("Points")), ')'), 4326)
FROM
    (
        SELECT '3.985 58.934, 4.56 61.2323, 5.4 63.234355, 3.25982 59.309, 4.5632 58.32423'::TEXT AS "C1"
    ) AS "T1";

来源：https://stackoverflow.com/questions/19220875/obtain-double-precision-values-from-inconsitent-strings-for-using-st-geomfromtex

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sql

postgresql

PostGIS