DXF Content¶

General preconditions:

import sys
import ezdxf

try:
    doc = ezdxf.readfile("your_dxf_file.dxf")
except IOError:
    print(f'Not a DXF file or a generic I/O error.')
    sys.exit(1)
except ezdxf.DXFStructureError:
    print(f'Invalid or corrupted DXF file.')
    sys.exit(2)
msp = doc.modelspace()

Get/Set Entity Color¶

The entity color is stored as ACI (AutoCAD Color Index):

aci = entity.dxf.color

Default value is 256 which means BYLAYER:

layer = doc.layers.get(entity.dxf.layer)
aci = layer.get_color()

The special get_color() method is required, because the color attribute Layer.dxf.color is misused as layer on/off flag, a negative color value means the layer is off.

ACI value 0 means BYBLOCK, which means the color from the block reference (INSERT entity).

Set color as ACI value as int in range [0, 256]:

entity.dxf.color = 1

The ACI value 7 has a special meaning, it is white on dark backgrounds and white on light backgrounds.

Get/Set Entity RGB Color¶

RGB true color values are supported since DXF R13 (AC1012), the 24-bit RGB value is stored as integer in the DXF attribute true_color:

# 24 bit binary value: 0bRRRRRRRRGGGGGGGGBBBBBBBB or hex value: 0xRRGGBB
# set true color value to red
entity.dxf.true_color = 0xFF0000

Use the helper functions from the ezdxf.colors module for RGB integer value handling:

from ezdxf import colors

entity.dxf.true_color = colors.rgb2int((0xFF, 0, 0))
r, g, b = colors.int2rgb(entity.dxf.true_color)

The RGB values of the AutoCAD default colors are not officially documented, but an accurate translation table is included in ezdxf:

# Warning: ACI value 256 (BYLAYER) raises an IndexError!
rgb24 = colors.DXF_DEFAULT_COLORS[aci]
print(f"RGB Hex Value: #{rgb24:06X}")
r, g, b = colors.int2rgb(rgb24)
print(f"RGB Channel Values: R={r:02X} G={g:02X} b={b:02X}")

If color and true_color values are set, BricsCAD and AutoCAD use the true_color value as display color for the entity.

Get/Set True Color as RGB-Tuple¶

Get/Set the true color value as (r, g, b)-tuple by the rgb property of the DXFGraphic entity:

# set true color value to red
entity.rgb = (0xFF, 0, 0)

# get true color values
r, g, b = entity.rgb

Get/Set Block Reference Attributes¶

Block references (Insert) can have attached attributes (Attrib), these are simple text annotations with an associated tag appended to the block reference.

Iterate over all appended attributes:

# get all INSERT entities with entity.dxf.name == "Part12"
blockrefs = msp.query('INSERT[name=="Part12"]')
if len(blockrefs):
    entity = blockrefs[0]  # process first entity found
    for attrib in entity.attribs:
        if attrib.dxf.tag == "diameter":  # identify attribute by tag
            attrib.dxf.text = "17mm"  # change attribute content

Get attribute by tag:

diameter = entity.get_attrib('diameter')
if diameter is not None:
    diameter.dxf.text = "17mm"

Adding XDATA to Entities¶

Adding XDATA as list of tuples (group code, value) by set_xdata(), overwrites data if already present:

doc.appids.new('YOUR_APPID')  # IMPORTANT: create an APP ID entry

circle = msp.add_circle((10, 10), 100)
circle.set_xdata(
    'YOUR_APPID',
    [
        (1000, 'your_web_link.org'),
        (1002, '{'),
        (1000, 'some text'),
        (1002, '{'),
        (1071, 1),
        (1002, '}'),
        (1002, '}')
    ])

For group code meaning see DXF reference section DXF Group Codes in Numerical Order Reference, valid group codes are in the range 1000 - 1071.

Method get_xdata() returns the extended data for an entity as Tags object.

Get Overridden DIMSTYLE Values from DIMENSION¶

In general the Dimension styling and config attributes are stored in the Dimstyle entity, but every attribute can be overridden for each DIMENSION entity individually, get overwritten values by the DimstyleOverride object as shown in the following example:

for dimension in msp.query('DIMENSION'):
    dimstyle_override = dimension.override()  # requires v0.12
    dimtol = dimstyle_override['dimtol']
    if dimtol:
        print(f'{str(dimension)} has tolerance values:')
        dimtp = dimstyle_override['dimtp']
        dimtm = dimstyle_override['dimtm']
        print(f'Upper tolerance: {dimtp}')
        print(f'Lower tolerance: {dimtm}')

The DimstyleOverride object returns the value of the underlying DIMSTYLE objects if the value in DIMENSION was not overwritten, or None if the value was neither defined in DIMSTYLE nor in DIMENSION.

Override DIMSTYLE Values for DIMENSION¶

Same as above, the DimstyleOverride object supports also overriding DIMSTYLE values. But just overriding this values have no effect on the graphical representation of the DIMENSION entity, because CAD applications just show the associated anonymous block which contains the graphical representation on the DIMENSION entity as simple DXF entities. Call the render method of the DimstyleOverride object to recreate this graphical representation by ezdxf, but ezdxf does not support all DIMENSION types and DIMVARS yet, and results will differ from AutoCAD or BricsCAD renderings.

dimstyle_override = dimension.override()
dimstyle_override.set_tolerance(0.1)

# delete associated geometry block
del doc.blocks[dimension.dxf.geometry]

# recreate geometry block
dimstyle_override.render()

How to Change the HATCH Pattern Origin Point¶

This code sets the origin of the first pattern line to the given origin and the origins of all remaining pattern lines relative to the first pattern line origin.

from ezdxf.entities import Hatch, Pattern
from ezdxf.math import Vec2

def shift_pattern_origin(hatch: Hatch, offset: Vec2):
    if isinstance(hatch.pattern, Pattern):
        for pattern_line in hatch.pattern.lines:
            pattern_line.base_point += offset

def reset_pattern_origin_of_first_pattern_line(hatch: Hatch, origin: Vec2):
    if isinstance(hatch.pattern, Pattern) and len(hatch.pattern.lines):
        first_pattern_line = hatch.pattern.lines[0]
        offset = origin - first_pattern_line.base_point
        shift_pattern_origin(hatch, offset)

How to Get the Length of a Spline or Polyline¶

There exist no analytical function to calculate the length of a B-spline, you have to approximate the curve and calculate the length of the polyline. The construction tool ezdxf.math.ConstructionPolyline is may be useful for that.

import ezdxf
from ezdxf.math import ConstructionPolyline

doc = ezdxf.new()
msp = doc.modelspace()
fit_points = [(0, 0, 0), (750, 500, 0), (1750, 500, 0), (2250, 1250, 0)]

spline = msp.add_spline(fit_points)
# Adjust the max. sagitta distance to your needs or run the calculation in a loop
# reducing the distance until the difference to the previous run is smaller
# than your expected precision:
polyline = ConstructionPolyline(spline.flattening(distance=0.1))
print(f"approximated length = {polyline.length:.2f}")

How to Resolve DXF Properties¶

Graphical properties of DXF entities (color, lineweight, …) are sometimes hard to resolve because of the complex possibilities to inherit properties from layers or blocks, or overriding them by ctb files.

The drawing add-on provides the RenderContext class that can be used to resolve properties of entities in the context of their use:

import ezdxf
from ezdxf.addons.drawing.properties import RenderContext

doc = ezdxf.new()
doc.layers.add("LINE", color=ezdxf.colors.RED)
msp = doc.modelspace()
line = msp.add_line((0, 0), (1, 0), dxfattribs={"layer": "LINE"})

ctx = RenderContext(doc)
ctx.set_current_layout(msp)
print(f"resolved RGB value: {ctx.resolve_color(line)}")

Output:

resolved RGB value: #ff0000

This works in most simple cases, resolving properties of objects in viewports or nested blocks requires additional information that is beyond the scope of a simple guide.