> For the complete documentation index, see [llms.txt](https://docs.openbrim.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.openbrim.org/developers/llm-guides/ai-cadd-drawing-guide.md).
# CADD Drawing Guide
## Overview
**CADD (Computer-Aided Design and Drafting)** in ParamML is used to create 2D technical drawings for cross-sections, elevations, and detail views. CADD drawings are parametric visualizations that automatically update when input parameters change.
**Key Concepts:**
* CADD drawings are defined using XML object types with `T="CADD"` as the container
* All shapes, lines, circles, and annotations are parametric
* Coordinates are defined using inline `X`, `Y` attributes
* Use `Guard` or `GuardX` for conditional rendering
* Use `T="Repeat"` for arrays of objects (e.g., reinforcement bars)
**CADD Object Types:**
1. [`T="CADD"`](#tcadd---drawing-container) - Drawing Container
2. [`T="CADDShape"`](#tcaddshape---2d-polygon) - 2D Polygon/Polyline
3. [`T="CADDCircle"`](#tcaddcircle---circle) - Circle/Reinforcement Bar
4. [`T="CADDDimensionLine"`](#tcadddimensionline---dimension-annotation) - Dimension Annotation
5. [`T="CADDLine"`](#tcaddline---open-polyline) - Open Polyline
6. [`T="CADDText"`](#tcaddtext---text-label) - Text Labels
***
## `T="CADD"` - Drawing Container
The main container for a CADD drawing. Contains all shapes, dimension lines, text, and other drawing elements.
**Attributes:**
* `N` (String): Name of the drawing
**Example:**
```xml
```
***
## `T="CADDShape"` - 2D Polygon
Draws closed polygons (filled shapes) using a series of points. Points are connected in order and automatically closed.
**Attributes:**
* `N` (String): Name of the shape
* `Color` (String, optional): Line/fill color (e.g., "black", "red", "rgb(255,0,0)")
* `Thickness` (Number, optional): Line thickness in pixels (default: 1)
* `LineStyle` (Array, optional): Dash pattern `[dashLength, gapLength]` (e.g., `[6,3]`, `[10,30]`)
* `Guard` or `GuardX` (Expression, optional): Conditional rendering
* `X`, `Y` (Number, optional): Shape offset from origin
**Children:** Multiple `T="Point"` objects defining the polygon vertices
**Example:**
```xml
```
**Notes:**
* Points are automatically closed (last point connects to first)
* Use `LineStyle="[dashLength,gapLength]"` for dashed/dotted lines
* Common patterns: `[6,3]` = short dash, `[10,30]` = long dash with gap
***
## `T="CADDCircle"` - Circle
Draws circles, typically used for reinforcement bars in concrete sections or other circular features.
**Attributes:**
* `N` (String, optional): Name of the circle
* `X`, `Y` (Number): Center coordinates
* `Radius` (Number or Parameter): Circle radius
* `Color` (String, optional): Fill/stroke color
* `Thickness` (Number, optional): Line thickness in pixels
* `LineStyle` (Array, optional): Dash pattern `[dashLength, gapLength]`
* `Segments` (Number, optional): Number of segments for smoothness (default: 36)
* `RZ` (Number, optional): Rotation angle in degrees (usually 0)
* `Guard` (Expression, optional): Conditional rendering
**Example:**
```xml
```
**Notes:**
* `Radius` can be defined as an attribute or as a child `` parameter
* Use `Segments="36"` for smooth circles (higher = smoother but slower)
* `RZ="0"` is standard for circles (rotation doesn't affect appearance)
***
## `T="CADDDimensionLine"` - Dimension Annotation
Draws dimension lines with arrows showing measurements. Requires exactly 3 points.
**Structure:**
* **Point 1:** Start of dimension (measured element's start)
* **Point 2:** End of dimension (measured element's end)
* **Point 3:** Identical to Point 2 + offset (determines dimension line placement)
**Dimension Direction Rules:**
* **Horizontal dimensions:** Points 1 and 2 have same Y, different X (left to right)
* **Vertical dimensions:** Points 1 and 2 have same X, different Y (bottom to top)
* **Offset:** Third point adds offset in perpendicular direction
**Attributes:**
* `N` (String): Name of the dimension
* `Guard` or `GuardX` (Expression, optional): Conditional rendering
**Children:** Exactly 3 `T="Point"` objects
**Example:**
```xml
```
**Notes:**
* Works best for horizontal and vertical dimensions
* Third point determines where dimension line appears relative to measured element
* For no offset, make third point identical to second point
***
## `T="CADDLine"` - Open Polyline
Draws open polylines (lines that don't close back to start point).
**Attributes:**
* `N` (String): Name of the line
* `Color` (String, optional): Line color
* `Thickness` (Number, optional): Line thickness in pixels
* `LineStyle` (Array, optional): Dash pattern
**Children:** Multiple `T="Point"` objects defining the line path
**Example:**
```xml
```
**Notes:**
* Unlike `CADDShape`, the line does NOT automatically close
* Use for reference lines, construction lines, or open paths
***
## `T="CADDText"` - Text Label
Adds text annotations to drawings. Text can include parameter values using `|paramName|` syntax.
**Attributes:**
* `N` (String): Name of the text object
* `X`, `Y` (Number): Text position
* `RZ` (Number, optional): Rotation angle in degrees
**Children Parameters:**
* `Color` (String, T="Text"): Text color
* `Thickness` (Number): Line thickness for text rendering
* `Size` (Number): Text size multiplier
* `Text` (String, T="Text"): The text content (can include `|paramName|` for values)
* `TextAlign` (Number): Alignment (0=left, 1=center, 2=right)
* `IsClosed` (String, T="Text"): Set to "T" for proper rendering
**Children Objects:** 3 `T="Point"` objects defining text box bounds
**Example:**
```xml
```
**Notes:**
* Use `|parameterName|` to embed parameter values in text
* Functions like `round()` can be used: `|round(value,2)|`
* `T="Text"` attribute is required for `Color`, `Text`, and `IsClosed` parameters
***
## CADD Drawing Best Practices
### 1. Conditional Rendering with Guards
Use `Guard` or `GuardX` attributes for conditional visibility of drawing elements.
**Example:**
```xml
```
**Notes:**
* Use `GuardX` or `Guard` for boolean conditions
* Multiple elements can have complementary guards
* Guards are evaluated dynamically when parameters change
***
### 2. Using Repeat for Arrays
Use `T="Repeat"` to create arrays of objects, such as reinforcement bars in concrete sections.
**Pattern:**
1. Calculate number of elements
2. Create Repeat loop
3. Use loop index `i` to position each element
**Example:**
```xml
```
**For Symmetric Arrays (Left and Right):**
```xml
```
**Notes:**
* `S` = Start index (usually 0)
* `E` = End index (inclusive)
* `I` = Increment (usually 1)
* `CTRL="i"` defines loop variable name
* `i="0"` sets initial value
***
## Common Coordinate System
**Typical convention for cross-sections:**
* **Y=0** at reference line (often top of section or top flange)
* **Negative Y** goes downward
* **X=0** at section centerline
* **Negative X** to the left, **Positive X** to the right
**Example:**
```xml
```
**Best Practice:** Document your coordinate system clearly in comments at the start of each CADD drawing.
***
## Summary
**CADD drawings in ParamML:**
* Use `T="CADD"` as container for all drawing elements
* Build shapes with `T="CADDShape"` (closed polygons) and `T="CADDCircle"` (circles)
* Add dimensions with `T="CADDDimensionLine"` (3 points: start, end, offset)
* Add open paths with `T="CADDLine"` (polylines)
* Add labels with `T="CADDText"` (supports parameter values with `|param|`)
* Use `Guard` for conditional rendering based on parameters
* Use `T="Repeat"` for arrays of objects (reinforcement bars, bolt patterns, etc.)
* Define coordinates consistently and document your coordinate system
* All CADD objects update automatically when parameters change
***
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