# API conventions

## Namespaces

| Namespace | Area |
| --- | --- |
| [`SCH`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/sch.md) | Schematic and schematic library documents, design objects, the schematic server. |
| [`PCB`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/pcb.md) | PCB and PCB library documents, design objects, the PCB server. |
| [`EDP`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/edp.md) | Projects, documents and the workspace (the project manager). |
| [`DXP`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/dxp.md) | The client application, servers, commands, views and notifications. |

## Entry points

Each editor is reached through a static property of `GlobalVars` in `Altium.SDK.dll` ([`SCH.GlobalVars`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/sch/GlobalVars.md), [`PCB.GlobalVars`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/pcb/GlobalVars.md), [`DXP.GlobalVars`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/dxp/GlobalVars.md)):

| Entry point | Type | Use |
| --- | --- | --- |
| `SCH.GlobalVars.SchServer` | [`ISch_ServerInterface`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/sch/ISch_ServerInterface.md) | Schematic documents, object creation, schematic preferences. |
| `PCB.GlobalVars.PCBServer` | [`IPCB_ServerInterface`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/pcb/IPCB_ServerInterface.md) | PCB documents and objects. |
| `DXP.GlobalVars.Client` | [`IClient`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/dxp/IClient.md) | The application: documents, views, commands. |

An entry point is `null` when its server is not loaded, so check before use.

## Interfaces and properties

The API is a set of interfaces; objects are never created with `new` but obtained from the servers, documents and
iterators. Interfaces form hierarchies: [`ISch_Component`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/sch/ISch_Component.md) is an
[`ISch_ParametrizedGroup`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/sch/ISch_ParametrizedGroup.md), which is an
[`ISch_GraphicalObject`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/sch/ISch_GraphicalObject.md), and so on. Each reference page lists the members
an interface inherits.

An object's state is read and written through accessor methods: `GetState_<Name>()` reads and
`SetState_<Name>(value)` writes. The reference shows each pair as one **property** page:

```csharp
TRotationBy90 orientation = component.GetState_Orientation();
component.SetState_Orientation(TRotationBy90.eRotate90);
```

A property with only a `GetState_` accessor is read-only. Some interfaces use other prefixes (`Get_`/`Set_`,
`GetProperty_`/`SetProperty_`, or plain `Get`/`Set` pairs such as `GetModified`/`SetModified`); they are grouped the
same way. Indexed properties take the index as the first argument (`GetState_AliasAt(index)`).

## Typed helper methods

Many methods are provided as extension methods of a static helper class next to the interface, such as
`ISch_ComponentHelper` for `ISch_Component`. The helpers return and accept the specific interface and enumeration
types, for example [`ISch_Designator`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/sch/ISch_Designator.md) from `GetState_SchDesignator()` and
[`TRotationBy90`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/sch/TRotationBy90.md) for `SetState_Orientation`. With `using SCH;` they are called
like interface methods:

```csharp
using SCH;

ISch_Designator designator = component.GetState_SchDesignator();
```

They can also be called as static methods: `ISch_ComponentHelper.GetState_SchDesignator(component)`. The reference
documents the typed form and notes on each page when a method comes from a helper class.

## Enumerations and object sets

Enumeration values carry their type's prefix convention, such as `eWire` and `eSchComponent` in
[`TObjectId`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/sch/TObjectId.md). Filters that take a set of values use the `*Set` classes, such as
`SCH.TObjectSet`:

```csharp
var objectSet = new SCH.TObjectSet();
objectSet.Add(SCH.TObjectId.eWire);
```

## Coordinates

Coordinates are integers in internal units. `EDP.Utils` converts between internal units and mils or millimetres
(`MilsToCoord`, `CoordToMils`, `MMsToCoord`, `CoordToMMs`); see [`EDP.Utils`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/edp/Utils.md).