WKT writer precision

[jaakkor2]

Using the Julia interface to GEOS, a non-consistent behavior of WKTWriter with rounding precision was observed. Original issue JuliaGeo/LibGEOS.jl#86. Used versions are LibGEOS v0.6.6 and GEOS_jll v3.9.0+0.

using LibGEOS
p = readgeom("POINT (654321.12345 0.1)");
writer = LibGEOS.WKTWriter(LibGEOS._context, trim=false, roundingprecision=3);
writegeom(p, writer)

gives

"POINT (654321.123 0.100)"

whereas

writer = LibGEOS.WKTWriter(LibGEOS._context, trim=true, roundingprecision=3);
writegeom(p, writer)

gives

"POINT (6.54e+05 0.1)"

Relevant libgeos code here

geos/src/io/WKTWriter.cpp

Lines 358 to 369 in 5b722cf

	WKTWriter::writeNumber(double d)
	{
	std::stringstream ss;
	if(! trim) {
	ss << std::fixed;
	}
	ss << std::setprecision(decimalPlaces >= 0 ? decimalPlaces : 0) << d;
	return ss.str();
	}

Judging from http://www.cplusplus.com/reference/iomanip/setprecision/ , if std::fixed is not in the stream, std::setprecision sets the significant digits.

[jaakkor2]

Same as above, now using pygeos

>>> import pygeos
>>> p = pygeos.Geometry("POINT (654321.12345 0.1)")
>>> pygeos.io.to_wkt(p, trim=False, rounding_precision=3)
'POINT (654321.123 0.100)'
>>> pygeos.io.to_wkt(p, trim=True, rounding_precision=3)
'POINT (6.54e+05 0.1)'                    

geos               conda-forge/win-64::geos-3.8.1-he025d50_0
pygeos             conda-forge/win-64::pygeos-0.8-py38h9764186_1

[pramsey]

Output in "trim" mode should be closer to "expectations" in master, as of 2376cd6