Coordinate System

Documentation Index

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• EMR coordinate system (digitizer / handwriting coordinates): a hardware-defined coordinate space from the EMR (Electro-Magnetic Resonance) handwriting system. It describes the absolute position of the pen tip on the sensing surface (2D and extended dimensions).
• Pixel coordinate system (screen coordinates): used to describe pixel positions in UI rendering.

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EMR Coordinate System (Digitizer / Handwriting)

• The unit is not pixels, but the digitizer’s hardware coordinate unit (you can think of it as a finer grid).
• It is typically higher precision: one screen pixel may correspond to multiple EMR units.
• Axes and origin may differ from screen coordinates (varies by device and orientation), so conversion is required.

• Strongly tied to handwriting data: stroke sampling points, outline points, angle points, etc. are usually more stable in EMR coordinates and better suited for storage and computation.
• Not equivalent to UI pixels: you cannot use EMR values as px for layout directly.

• Geometry computation for strokes/elements: move, scale, etc.
• Working with native cached point data accessors (large point sets are better represented in EMR coordinates).

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Pixel Coordinate System (Screen)

• The unit is pixels (px).
• Conventionally, top-left is the origin: x increases to the right, y increases downward.
• width/height represent the pixel dimensions of the screen/page (e.g., A5X often uses 1404×1872, Manta often uses 1920×2560).

• Strongly tied to UI rendering: layout, scaling, rotation, and page composition can change where the “same logical point” ends up in pixel space.
• Suitable for UI interactions: tap/drag positions, view layout rectangles, screenshot pixels, etc.

• Drawing/positioning UI elements in React Native (e.g., popups, buttons, selection boxes)
• Interactions based on touch/tap position
• Working with API-returned page sizes (pixels), e.g. PluginFileAPI.getPageSize(...)

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Why Two Coordinate Systems?

• The EMR pen is sampled by digitizer hardware and produces high-precision handwriting coordinates. It does not depend on UI rendering and does not change with screen scaling/layout.
• Screen rendering is driven by the display system (Android/rendering engine) and uses pixel coordinates. It is affected by resolution, rotation, page composition, scaling, and other display strategies.

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Comparison

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Conversion in the SDK

import { PluginFileAPI, PointUtils } from 'sn-plugin-lib';

/**
 * Convert a pixel-coordinate point to an EMR-coordinate point.
 */
export async function pixelToEmr(notePath: string, page: number, pixelPoint: { x: number; y: number }) {
  const res = await PluginFileAPI.getPageSize(notePath, page);
  if (!res?.success || !res.result) {
    throw new Error('Failed to get page pixel size');
  }

  return PointUtils.androidPoint2Emr(pixelPoint, res.result);
}

/**
 * Convert an EMR-coordinate point to a pixel-coordinate point.
 */
export async function emrToPixel(notePath: string, page: number, emrPoint: { x: number; y: number }) {
  const res = await PluginFileAPI.getPageSize(notePath, page);
  if (!res?.success || !res.result) {
    throw new Error('Failed to get page pixel size');
  }

  return PointUtils.emrPoint2Android(emrPoint, res.result);
}

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Mapping Range and Notes