Converting dxf to shp and keep elevation information QGIS

Question

I want to create a QGIS plugin that convert dxf files to shp. I didn't use DXF2SHP plugin in QGIS because I have some specific needs. I'm using gdal_ogr library.

dxfdat="*.dxf"
shpLinestring="*.shp"

opt1="-skipfailure  --config DXF_MERGE_BLOCK_GEOMETRIES FALSE --config DXF_INLINE_BLOCKS TRUE -gcp  z  -nlt LINESTRING "
sql1= "-sql \"SELECT *,ogr_style from entities where OGR_GEOMETRY LIKE '%LINESTRING%'\" "
processing.runalg('gdalogr:convertformat',dxfdat , 0,opt1 + sql1, shpLinestring)

I can make the convertion but is it possible to keep the elevation attribute from dxf file ?

Answer 1

The DXF is real 3D (Z-value not attribute)? Then test the following:

-dim val:(starting with GDAL 1.10) Force the coordinate dimension to val (valid values are XY, XYZ, XYM, and XYZM - for backwards compatibility 2 is an alias for XY and 3 is an alias for XYZ). This affects both the layer geometry type, and feature geometries. Starting with GDAL 1.11, the value can be set to "layer_dim" to instruct feature geometries to be promoted to the coordinate dimension declared by the layer. Support for M was added in GDAL 2.1

processing.runalg('gdalogr:convertformat',dxfdat , 0,sql1 + opt1 + ' -dim XYZ', shpLinestring)

A polyline usually has different z-values. As an attribute, you can only put one Z value for the entire line. If that's enough for you, create a new field in the field calculator:

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Another way with SQLite-Synax: Write the z-Value from the first point of LineString to Attribut

import processing
dxfdat="d:/tar/3d.dxf"
shpLinestring="d:/tar/1.shp"

opt1="-skipfailure  --config DXF_MERGE_BLOCK_GEOMETRIES FALSE --config DXF_INLINE_BLOCKS TRUE -dim XYZ  -nlt LINESTRING "
sql1= "-dialect sqlite -sql \"SELECT *,ST_Z(ST_StartPoint (geometry)) as elevation, ogr_style from entities where GeometryType(geometry) LIKE '%LINESTRING%'\" "
processing.runalg('gdalogr:convertformat',dxfdat , 0,opt1 + sql1, shpLinestring)