In STEP, FDT are also known as GD&T for Geometrical Dimensioning And Tolerancing.
Notice : in STEP files, semantic description and graphic display of FDT are described separately.
FDT can be read as Symbols (Graphics) or as Semantics+Graphics.
Settings : after call to Dtk_API::StartAPI,
- use call form of API : StepReader::SetModeReadFDT (inMode) ,

Where inMode is an integer value, it can have one of these values :

0 : no reading of FDT and Views
1 : read views, and FDT as graphic only
2 or 3 (2 : default from V2019.2) : read views, and FDT as graphic + semantic
(from V2023.2) for case of dual graphics of FDT (a "frozen" one and a placeholder) :
2 to prefer the "frozen" graphics
3 to prefer the placeholder

FDT as graphic + semantic : because of the organization of FDT in STEP, they are read in a specific way.

In STEP,

generally, graphic and semantic parts of a FDT are completely separated, then globally associated
a graphic FDT has NO text (there is a possibility of texts but it is now deprecated) and NO leader line, just a set of polylines or triangles
a FDT can be written as semantic+graphic, or graphic only
a capability of "semantics with embedded graphics" (known as "placeholder") comes in AP242 Edition 2 but its use will remain optional
in the same move, a FDT can be written with 2 graphics : one frozen (curves, tessellation) and one placeholder

When reading FDT in semantic mode ( inMode=2 ), the Dtk_Info of the Dtk_Fdt (and of the Dtk_Node) has an attribute "Dtk_SemanticFdt" (an integer)

If the FDT is graphic only (no semantics at all), a Dtk_Node of type FDT is created, "Dtk_SemanticFdt" = -1
If the FDT is semantic+graphic , with frozen graphics (as curves or tessellation) : 2 Dtk_Nodes of type FDT are created as follows :
– the Dtk_Node for the FDT brings the SEMANTIC FDT, also the Node Connectors to the affected geometries, but not to be displayed : "Dtk_SemanticFdt" = 1 , the FDT is set Blanked (BlankedStatus=1)
– it has a subnode, another Dtk_Node of type FDT, which brings the GRAPHIC FDT (no semantics, no geometrical link), ready to be displayed : "Dtk_SemanticFdt" = 0 , the FDT is visible (BlankedStatus=0)
If the FDT is semantic+placeholder graphics (= minimal graphics) : the graphic part is recomputed when reading :
– one Dtk_Node of type FDT is created, ready to be displayed :"Dtk_SemanticFdt" = 2, no subnode, the FDT is visible
It can occur that a semantic FDT has no graphics at all : same as above but "Dtk_SemanticFdt" = 3 to distinguish this case
In case of dual graphics (a FDT is written with both a frozen graphics and a placeholder) : one graphics is selected; before V2023.2 the frozen graphics, from V2023.2 choice is made according to stepr_SetModeReadFdt (value 2 or 3)

General Information on FDT

STEP Entities	DATAKIT Class	Remarks
product (id=FDT standard) + document_product_equivalence + product_definition_context_association ..	(Dtk_Component:)Dtk_Info: Dtk_PMIGlobalStandard	Fdt Standard : ISO / ASME
measure_representation_item used in a semantic FDT	(Dtk_Text) length/angle value with unit
value_format_type_qualifier	Dtk_Text:Dtk_Info: DtkPrecision	nb of significant digits

Graphic and Textual Data of FDT

FDT as Symbols

STEP Entities	DATAKIT Class	Remarks
draughting_model with no camera_model	set of Dtk_Node	graphic part of the annotations attached to the model See also Views
callout or sub-type, alone	Dtk_Fdt with 2dEntity as Dtk_Symbol	(in graphic read mode, semantics is ignored even if present)
callout or sub-type, associated to a semantic FDT	Dtk_Fdt : graphical part (recorded in the 2dEntity)	(semantic read mode only)
annotation_occurrence or sub-type alone	Dtk_Fdt with 2dEntity as Dtk_Symbol	(case of graphics described by polylines)
each annotation_occurrence or sub-type	a graphic item of the Dtk_Fdt	Items are : texts, leaders, other geometries
annotation_occurrence_relationship / _associativity	Dtk_Fdt with 2dEntity as Dtk_Symbol	(used for graphics as polylines with no semantics)
each annotation_placeholder_occurrence	graphic part of Dtk_Fdt (not separated)	The graphics is rebuilt from minimal informations of the placeholder (position, text size, attachment points)

Geometrical Links of FDT

STEP Entities	DATAKIT Class	Remarks
shape_aspect and sub-types	a Geometrical Link of the Dtk_Fdt or a Dtk_NodeConnector (only within a Part)	to designate a 3D item : face, edge, etc
composite_shape_aspect	several Geometrical Links of the Dtk_Fdt or Dtk_NodeConectors	cumulates several shape_aspect
component_path_shape_aspect + multi_level_reference_designator	Dtk_NodeConnector with Path	AP242 - only within a same file <! shape_aspect_associativity or shape_aspect_relationship : semantic only >
shape_definition_representation on shape_aspect, or geometric_item_specific_usage		designates the 3D item(s)
draughting_model_item_association		associates a FDT - to a geometry via a shape_aspect, - or to a component as a whole via a product_definition_shape Also used in STEP to associate the semantic and graphic parts of a FDT

Leader Curve of FDT

STEP Entities	DATAKIT Class	Remarks
annotation_symbol_occurrence / terminator_symbol	attaches a Terminator to the Leader Curve	designates the geometry with an annotation_curve_occurrence
annotation_symbol_occurrence not a terminator_symbol	not supported	(for a symbol without a leader curve)
annotation_curve_occurrence and leader_curve	The geometry of the Leader Curve	(see below for geometries of FDT)
defined_symbol	Definition of the terminator symbol	(designates type, size, style)
pre_defined_terminator_symbol	type of the symbol
symbol_target	size of the symbol
symbol_style , symbol_colour	style of the symbol (color)

Other Geometries of FDT

STEP Entities	DATAKIT Class	Remarks
annotation_curve_occurrence or annotation_occurrence (basic type)	the geometries of the FDT	lists geometrical items, see hereafter
tessellated_annotation_curve_occurrence , tessellated_geometric_set , tessellated_curve_set and content	the geometries of the FDT (wireframe)	AP242 - converted to polylines (Dtk_Polyline)
triangulated_surface_set and sub-types	the geometries of the FDT (filled faces)	AP242 - set of Dtk_Polyline with Dtk_Info: PolygonCurve=1
point_style , pre_defined_marker	style of a point (color, marker)	common to the whole annotation
curve_style , draughting_pre_defined_curve_font	style of a curve (color, thickness, font)	common to the whole annotation
geometric_curve_set	as its list of items	if several geometrical items in an annotation
geometric_set	as its list of items	variant used for filled polylines
line or polyline or circle or trimmed_curve	converted to Polyline in the Dtk_Fdt	individual geometrical item
face_surface with* polyloop*	converted to outline Polylines in the Dtk_Fdt	for a filled polyline

Texts of FDT

STEP Entities	DATAKIT Class	Remarks
annotation_text_occurrence	Dtk_CompositeText, parameters common to all its texts	designates one or several texts together
text_style_with_box_characteristics	Definition of characters	(height, width, slant, rotate angle)
text_style_for_defined_font	Style of the texts (color)
composite_text	case of several Dtk_Text
text_literal	a Dtk_Text, general case
text_literal_with_delineation	a Dtk_Text, with a frame
text_literal_with_extent + planar_extent	a Dtk_Text with specific size for outer box	can be combined with delineation

Semantic Data of FDT

FDT Standard

STEP Entities	DATAKIT Class	Remarks
product + application_context "geometrical dimensioning and tolerancing rpresentation" document_product_equivalence with name="equivalence"	FDT Standard in product.name, see below	defines the FDT Standard
product.name = "ISO 1101"	FDT Standard : ISO
product.name starting by "ASME Y14"	FDT Standard : ASME

Datum Elements

STEP Entities	DATAKIT Class	Remarks
datum + datum_feature	Dtk_Fdt + Dtk_Symbol typed TypeDatum (Simple Datum)
placed_datum_target_feature , datum_target	Dtk_Fdt + Dtk_DatumTarget

Geometrical Tolerances

STEP Entities	DATAKIT Class	Remarks
geometric_tolerance_relationship	a Dtk_GeometricalTolerance with several Dtk_ToleranceSpecification's
geometric_tolerance with various sub-types	a Dtk_GeometricalTolerance with a Dtk_ToleranceSpecification	type and other data : see below
angularity_tolerance	type Angularity
roundness_tolerance	type Circularity
circular_runout_tolerance	type CircularRunout
coaxiality_tolerance	type CircularRunout
concentricity_tolerance	type Concentricity
cylindricity_tolerance	type Cylindricity
flatness_tolerance	type Flatness
line_profile_tolerance	type LineProfile
surface_profile_tolerance	type SurfaceProfile
parallelism_tolerance	type Parallelism
perpendicularity_tolerance	type Perpendicularity
position_tolerance	type Position
straightness_tolerance	type Straightness
symmetry_tolerance	type Symmetry
total_runout_tolerance	type TotalRunout
+ combined sub-type modified_geometric_tolerance + Material Modifier	in the Dtk_ToleranceSpecification : Material Modifier	AP203/AP214 - can be Ⓛ Ⓜ Ⓡ
+ combined sub-type* geometric_tolerance_with_modifiers + list of Modifier(s)*	in the Dtk_ToleranceSpecification : Modifiers (in the value of the text)	AP242
tolerance_zone + tolerance_zone_form	in the Dtk_ToleranceSpecification : value prefixed by diameter or spherical diameter info
projected_zone_definition	in the Dtk_ToleranceSpecification : modifier for projection ( Ⓟ ) + value
+ combined sub-type* unequally_disposed_geometric_tolerance*	in the Dtk_ToleranceSpecification : - if FDT Standard is ISO : UZ[..] with value - if FDT Standard is ASME : Ⓤ with value
+ combined sub-type* geometric_tolerance_with_defined_unit*	in the Dtk_ToleranceSpecification : defined unit	(after the value, notation "/val1[Xval2]")
+ combined sub-type* geometric_tolerance_with_maximum_tolerance*	in the Dtk_ToleranceSpecification : "MAX val" (end of the value text)	AP242
datum_reference (if no material modifier) or referenced_modified_datum (if material modifier)	a Reference Block to one Datum	AP203/AP214
common_datum + datum_reference or referenced_modified_datum	a Reference Block to several Datums	AP203/AP214
(geometric_tolerance_with_datum_reference +) datum_system	list of a Reference Blocks	AP242
datum_reference_compartment	a Reference Block to a Datum	AP242
datum_reference_compartment + common_datum_list	a Reference Block to several Datums	AP242

Dimensions

STEP Entities	DATAKIT Class	Remarks
dimensional_size , angular_size	Dtk_Dimension	on one set of 3d items
dimensional_location , angular_location	Dtk_Dimension	between 2 sets of 3D items
field "name" of the dimension	its DimensionType
for each value : length_measure_with_unit , plane_angle_measure_with_unit	details below
one value in the dimension, named "nominal value" (alone or with a tolerance)	in the Dtk_Dimension : nominal value
one value + modifier "theoretical"	in the Dtk_Dimension : nominal value in a rectangular frame
one value + modifier "auxiliary"	in the Dtk_Dimension : nominal value between parentheses
plus_minus_tolerance + tolerance_value	in the Dtk_Dimension : tolerance as plus value and minus value
plus_minus_tolerance + limits_and_fits	in the Dtk_Dimension : tolerance as tabulated (standardized text)
one value , named "lower limit" AND one value , named "upper limit"	in the Dtk_Dimension : lower value and upper value
one value + type_qualifier "minimum"	in the Dtk_Dimension : lower value only (MINI)
one value + type_qualifier "maximum"	in the Dtk_Dimension : upper value only (MAXI)
modifier : descriptive_representation_item listed in the</> shape_dimension_representation	in the Dtk_Dimension : additional prefix or suffix
name of the shape_dimension_representation	in the Dtk_Dimension : additional suffix	independency gives Ⓘ envelope gives Ⓔ

Notes as Editable Text

STEP Entities

DATAKIT Class

Remarks

property_definition_representation with property_definition, name = "semantic text"

Dtk_Symbol

Texts themselves are in descriptive_representation_item

Associated Data

Construction Geometries

STEP Entities

DATAKIT Class

Remarks

constructive_geometry_representation + axis2_placement_3d

Dtk_AxisSystem

constructive_geometry_representation with a geometry

a Dtk_Body : in a Dtk_Node type Body subtype NODE_FDT

infinite plane : gives a Dtk_Face based on a Dtk_Plane, with no loop

constructive_geometry_representation_relationship

link to the Component

Views and Captures

STEP Entities	DATAKIT Class	Remarks
draughting_model with camera_model(s)	Per camera_model : one Dtk_ModelDisplay	lists the annotations in the view
camera_model_d3	Dtk_ModelDisplay
camera_model_d3_multi_clipping + plane	Dtk_ModelDisplay + clipping plane	Section View (limitation :one plane)
view_volume , planar_box	parameters of the Dtk_ModelDisplay	(position, axes, scale)
model_geometric_view , field name	prior to define the name of the Dtk_ModelDisplay	from AP242E3
default_model_geometric_view	status "Active" of the Dtk_ModelDisplay	from AP242E3
context_dependent_over_riding_styled_item + invisibility listed in the draughting_model	in the Dtk_Node : NodeConnector "forceHidden" with instance path
context_dependent_over_riding_styled_item + styled_item(color) listed in the draughting_model	in the root Dtk_Component : Dtk_Override/Dtk_OverrideSet with Dtk_Info (color) and NodeConnector (instance path)	if Override mode is active

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