diff --git a/src/fvr/cad.py b/src/fvr/cad.py
new file mode 100644
index 0000000..757376c
--- /dev/null
+++ b/src/fvr/cad.py
@@ -0,0 +1,287 @@
+import ezdxf
+import ezdxf.addons.drawing
+import ezdxf.addons.drawing.svg
+import ezdxf.addons.drawing.properties
+
+# dxfattribs={'color': 1}
+# color
+# 0: white
+# 1: red
+# 2: yellow
+# 3: green
+# 4: cyan
+# 5: blue
+# 6: magenta
+# 7: white (as 0 - on dark background, black on light background)
+# 8: gray
+# 9: light-gray
+#
+# 10 - 19 shades of red (10 red same as 1)
+# ...
+# 240 - 249 shades of red (slightly blue shift)
+# 250 - 255 shades of gray
+# see https://ezdxf.mozman.at/docs/concepts/aci.html#aci
+
+class doc:
+  """
+  contour scale and dimension scale
+
+  to create a line in dimension scale = (x, y)/sc*sd
+  """
+
+  # scale
+  _sd = 1/1  # scale dimension
+  _sc = 1/1  # scale countour
+
+  def __init__(self, setup=True, scale=1, sc=1, sd=1):
+    """
+    Args:
+      scale: scale line and font size of contour and dimensions
+      sc: scale contour
+      sd: scale dimension position
+    """
+    self.doc = ezdxf.new(dxfversion='AC1032', setup=setup)
+    self.msp = self.doc.modelspace()
+    layercon = self.doc.layers.add("con")
+    layercon.color = 0
+    layercon.dxf.lineweight = 75
+    layerdim = self.doc.layers.add("dim")
+    layerdim.color = 6
+    layerdim.dxf.lineweight = 35
+    # dimstyle = self.doc.dimstyles.add("dim")
+    # dimstyle.set_text_align(valign='center', vshift=1)
+    # dimstyle.set_dimline_format(color=6)
+    # dimstyle.set_extline_format(color=6)
+    self.sc = self._sc*sc*scale
+    self.sd = self._sd*sd*scale
+    #self.sd = self._sd*sd*scale/sc
+    #self.sd = sc/(self._sd*sd)*scale
+    self.dims = []
+    self._dimstyle()
+
+  def _dimstyle(self):
+    self.dimstyle = {
+      'dimtxsty': 'Standard',
+      # text
+      'dimtxt': 0.35,  # 0.35mm line weight
+      'dimclrt': 6,    # text color ## set via layer
+      # arrow
+      'dimtsz': 0,     # set tick size to 0 to enable arrow usage
+      'dimasz': 0.35,  # arrow size in drawing units
+      'dimblk': ezdxf.ARROWS.closed_filled,  # arrows
+      # dimension line
+      'dimclrd': 6,    # color ## set via layer
+      'dimlwd': 35,    # 0.35mm line weight
+      # extension line
+      'dimclre': 6,    # color ## set via layer
+      'dimlwe': 35,    # 0.35mm line weight
+      'dimexe': 0.15,  # length above dimension line
+      'dimex0': 0.10,  # offset from measurement point
+      'dimlfac': 1/self.sc,  # scale factor for dimension measurements.
+      #'dimlfac': 100*self._sdc*self.sd,
+    }
+
+  def line(
+      self, p1, p2, color=None, lineweight=None, linetype='CONTINUOUS',
+      layer=None, dxfattribs=None, shift=(0, 0)):
+    """
+    Args:
+      p1: (x, y)
+      p2: (x, y)
+      color: defaults to 0
+      lineweight: defaults to 75, corresponds to a 0.75 mm linewidth (conversion 1/100).
+      linetype: 'DASHED2'
+      leyer: e.g. 'con' for contour, 'dim' dimension
+    """
+    _dxfattribs={'layer': 'con', 'linetype': linetype}
+    if layer is not None: _dxfattribs.update({'layer': layer})
+    if color is not None: _dxfattribs.update({'color': color})
+    if lineweight is not None: _dxfattribs.update({'lineweight': lineweight})
+    if dxfattribs is not None:
+      _dxfattribs = dxfattribs
+    p1 = ((p1[0]+shift[0])*self.sc, (p1[1]+shift[1])*self.sc)
+    p2 = ((p2[0]+shift[0])*self.sc, (p2[1]+shift[1])*self.sc)
+    self.msp.add_line(p1, p2, dxfattribs=_dxfattribs)
+
+  def polyline(
+      self, pts, close=False, color=None, lineweight=None, linetype='CONTINUOUS',
+      layer=None, dxfattribs=None, shift=(0, 0)):
+    """
+    Args:
+      pts: [(x1, y1), (x2, y2), ...]
+    """
+    _dxfattribs={'layer': 'con', 'linetype': linetype}
+    if layer is not None: _dxfattribs.update({'layer': layer})
+    if color is not None: _dxfattribs.update({'color': color})
+    if lineweight is not None: _dxfattribs.update({'lineweight': lineweight})
+    if dxfattribs is not None:
+      _dxfattribs = dxfattribs
+    pts = [((x+shift[0])*self.sc, (y+shift[1])*self.sc) for x, y in pts]
+    self.msp.add_lwpolyline(pts, close=close, dxfattribs=_dxfattribs)
+
+  def circle(
+      self, pt, radius, color=None, lineweight=None, linetype='CONTINUOUS',
+      layer=None, dxfattribs=None):
+    """
+    Args:
+      pt: (x, y)
+      radius:
+    """
+    _dxfattribs={'layer': 'con', 'linetype': linetype}
+    if layer is not None: _dxfattribs.update({'layer': layer})
+    if color is not None: _dxfattribs.update({'color': color})
+    if lineweight is not None: _dxfattribs.update({'lineweight': lineweight})
+    if dxfattribs is not None:
+      _dxfattribs = dxfattribs
+    pt = [i*self.sc for i in pt]
+    radius *= self.sc
+    self.msp.add_circle(pt, radius=radius, dxfattribs=_dxfattribs)
+
+  def linear_dim(self, base, p1, p2, text, dim_shift=None):
+    """
+    Args:
+      base: (x, y) location of the dimension line in contour scale.
+        Use dim_shift to be able to scale contour only and not the dimension.
+      p1: (x, y) 1st measurement point
+      p2: (x, y) 2nd measurement point
+      dim_shift: shift (dx, dy), in dimension scale not contour scale
+    """
+    _dxfattribs={'layer': 'dim'}
+    base = [i*self.sc for i in base]
+    p1, p2 = [i*self.sc for i in p1], [i*self.sc for i in p2]
+    if dim_shift is not None:
+      dim_shift = [i*self.sd for i in dim_shift]
+      base = ((base[0]+dim_shift[0]), (base[1]+dim_shift[1]))
+    dim = self.msp.add_linear_dim(base=base, p1=p1, p2=p2, text=text,
+      # dimstyle="EZDXF",  # default dimension style
+      # dimstyle="dim",
+      override=self.dimstyle,
+      dxfattribs=_dxfattribs,
+    )
+    self.dims.append(dim)
+    # dim.render() below when fetching the rendering
+
+  def aligned_dim(
+      self, p1, p2, distance, text, text_rotation=None, text_shifth=0,
+      text_shiftv=0, arrow1=None, arrow2=None):
+    """
+    Args:
+      p1: (x, y) 1st measurement point
+      p2: (x, y) 2nd measurement point
+      distance: NOTE! in dimension scale not contour scale
+      text:
+      text_rotation: global rotation in in degree
+      text_shifth: shift parallel to the dimension line
+      text_shiftv: shift perpendicular to the dimension line
+      arrow1: 'DOTSMALL'
+      arrow2: 'DOTSMALL'
+    """
+    _dxfattribs = {'layer': 'dim'}
+    if text_rotation is not None: _dxfattribs.update({'text_rotation': text_rotation})
+    p1, p2 = [i*self.sc for i in p1], [i*self.sc for i in p2]
+    # distance  # not distance, this is in dimension scale
+    distance *= self.sd
+    text_shifth *= self.sd
+    text_shiftv *= self.sd
+    dim = self.msp.add_aligned_dim(
+      p1=p1, p2=p2, distance=distance, text=text, override=self.dimstyle,
+      dxfattribs=_dxfattribs)
+    dim.shift_text(dh=text_shifth, dv=text_shiftv)
+    if arrow1 is not None:
+      dim.set_arrows(blk1=arrow1)
+    if arrow2 is not None:
+      dim.set_arrows(blk2=arrow2)
+    self.dims.append(dim)
+    # dim.render() below when fetching the rendering
+
+  def leader(
+      self, pts=(0, 0), layer=None):
+    """
+    Args:
+      pts: [(x1, y1), (x2, y2), ...]
+      distance: NOTE! in dimension scale not contour scale
+      text:
+      text_rotation: global rotation in in degree
+      text_shifth: shift parallel to the dimension line
+      text_shiftv: shift perpendicular to the dimension line
+      arrow1: 'DOTSMALL'
+      arrow2: 'DOTSMALL'
+    """
+    _dxfattribs = {'layer': 'dim'}
+    pts = [((x)*self.sc, (y)*self.sc) for x, y in pts]
+    dim = self.msp.add_leader(
+      vertices=pts, override=self.dimstyle,
+      dxfattribs=_dxfattribs)
+
+  def text(
+      self, text, pt=(0, 0), height=0.35, rotation=0, layer=None):
+    """
+    Args:
+      p1: (x, y) 1st measurement point
+      p2: (x, y) 2nd measurement point
+      distance: NOTE! in dimension scale not contour scale
+      text:
+      text_rotation: global rotation in in degree
+      text_shifth: shift parallel to the dimension line
+      text_shiftv: shift perpendicular to the dimension line
+      arrow1: 'DOTSMALL'
+      arrow2: 'DOTSMALL'
+    """
+    _dxfattribs = {'layer': ''}
+    if layer is not None: _dxfattribs.update({'layer': layer})
+    pt = [i*self.sc for i in pt]
+    dim = self.msp.add_text(
+      text=text, height=height, rotation=rotation, dxfattribs=_dxfattribs)
+    # set position and alignment
+    dim.set_placement(
+      pt,
+      # align=ezdxf.enums.TextEntityAlignment.MIDDLE_CENTER,
+      # align=ezdxf.enums.TextEntityAlignment.MIDDLE_LEFT,
+      align=ezdxf.enums.TextEntityAlignment.LEFT,
+    )
+
+  def render_dims(self):
+    # Necessary second step to create the BLOCK entity with the dimension geometry.
+    # Additional processing of the DIMENSION entity could happen between adding
+    # the entity and the rendering call.
+    [dim.render() for dim in self.dims]
+
+  def save_dxf(self, filename="output.dxf"):
+    self.render_dims()
+    self.doc.saveas(filename)
+
+  def export_svg_string(self, background="#21283000"):
+    self.render_dims()
+    doc = self.doc
+    msp = self.msp
+    context = ezdxf.addons.drawing.RenderContext(doc)
+    backend = ezdxf.addons.drawing.svg.SVGBackend()
+    layoutprops = ezdxf.addons.drawing.properties.LayoutProperties.from_layout(msp)
+    layoutprops.set_colors(background)  # set background, transparent "#21283000", default "#212830"
+    frontend = ezdxf.addons.drawing.Frontend(context, backend)
+    frontend.draw_layout(msp, layout_properties=layoutprops)
+    # page size
+    # page = ezdxf.addons.drawing.layout.Page(
+    #   210, 297, units=ezdxf.addons.drawing.layout.Units.mm,
+    #   margins=ezdxf.addons.drawing.layout.Margins.all(20))
+    # svg_string = backend.get_string(page)
+    # autodetect page size
+    page = ezdxf.addons.drawing.layout.Page(
+      0, 0, units=ezdxf.addons.drawing.layout.Units.mm,
+      margins=ezdxf.addons.drawing.layout.Margins.all(2))
+    svg_string = backend.get_string(
+      page, settings=ezdxf.addons.drawing.layout.Settings(scale=20/1, fit_page=False))
+    return svg_string
+
+  def export_svg(self, filename="output.svg"):
+    doc = self.doc
+    svg_string = export_svg_string(doc)
+    with open(filename, "wt", encoding="utf8") as fh:
+      fh.write(svg_string)
+
+if __name__ == '__main__':
+  dd = doc()
+  # detects the bounding box for any Iterable[DXFEntity]
+  bounding_box = ezdxf.bbox.extents(dd.modelspace())
+  print(bounding_box)
+  print('\n'.join([f"{i}" for i in dir(dd.doc)]))