Transforming wkt to wkt

Question

I am looking for a way to transform WKT-strings from EPSG:31467 to EPSG:25832 using a ntv2-grid (and without using a gui).

Example:

POLYGON((3413732.42 5318051.77,3413747.65 5318049.04,3413750.05 5318062.33,3413734.96 5318065.13,3413732.42 5318051.77))

For shapefiles I use ogr2ogr but have no clue how to transform WKT strings.

Answer 1

You cannot Directly transform WKT Strings with orgr2ogr.

But you can read and write WKT Geometries as part of the CSV format, see http://www.gdal.org/drv_csv.html and https://trac.osgeo.org/gdal/ticket/3145.

So you could write a wrapper function to create and write temporary CSV files from your WKT and parse the result.

---

Bash:

function wkt_transform {
    test $# -eq 3 || { >&2 echo -e "Usage:\n    wkt_transform WKT_STRING S_SRS T_SRS"; return 1; }
    tmpcsv=$(mktemp -u).csv
    echo -e "id,WKT\n1,\"${1}\"" > $tmpcsv
    ogr2ogr -f CSV -s_srs $2 -t_srs $3 /vsistdout/ $tmpcsv \
        -oo GEOM_POSSIBLE_NAMES=WKT -oo KEEP_GEOM_COLUMNS=false -lco GEOMETRY=AS_WKT \
        | grep --color=never -Po '(?<=^")[^"]*'
    rm $tmpcsv
}

Usage:

wkt_transform WKT_STRING S_SRS T_SRS

Example:

wkt_transform "POLYGON ((413690.7172644 5316365.30576906,413705.941127458 5316362.57674411,413708.340269542 5316375.86138841,413693.256350828 5316378.66038415,413690.7172644 5316365.30576906))" EPSG:31467 EPSG:25832

Result:

POLYGON ((-2575200.84161077 5311948.51145795,-2575186.10407411 5311945.92874797,-2575183.55059298 5311959.14935342,-2575198.15104713 5311961.80277235,-2575200.84161077 5311948.51145795))

---

Python alternative:

import sys, re
from osgeo import ogr
from osgeo import osr

wkt = sys.argv[1]
s_srs = int(re.sub("[^0-9]", "", sys.argv[2]))
t_srs = int(re.sub("[^0-9]", "", sys.argv[3]))

source = osr.SpatialReference()
source.ImportFromEPSG(s_srs)

target = osr.SpatialReference()
target.ImportFromEPSG(t_srs)

transform = osr.CoordinateTransformation(source, target)

geom = ogr.CreateGeometryFromWkt(wkt)
geom.Transform(transform)

print geom.ExportToWkt()

Example:

transform.py "POLYGON ((413690.7172644 5316365.30576906,413705.941127458 5316362.57674411,413708.340269542 5316375.86138841,413693.256350828 5316378.66038415,413690.7172644 5316365.30576906))" 31467 25832