Orthogonal Measure QGIS Plugin v0.1

Author: Darko Nedic · Contact: office@geo-biz.com · License: GNU GPL v2+ · Min. QGIS: 3.0

Overview

Orthogonal Measure is a QGIS plugin that lets you define a local orthogonal coordinate system directly on the map canvas and then construct points by entering X and Y offsets in metres. It is designed for surveyors, civil engineers, and GIS professionals who need to quickly stake out or digitize points relative to a custom baseline — without leaving QGIS.

The plugin works correctly in any CRS (projected or geographic) because all offset calculations use ellipsoidal ground distances.

How It Works

1. Coordinate System Definition

Point 1 — Origin (0, 0): Click anywhere on the map to place the origin of your local system.
Point 2 — Y-axis direction: Click a second point. The direction from Point 1 to Point 2 defines the positive Y-axis.
X-axis is automatically computed as perpendicular to the Y-axis, rotated 90° clockwise.

Both axes are visualized on the map canvas:

Axis	Colour	Positive direction	Negative direction
Y	Blue	Solid dashed line	Faint dotted line
X	Green	Solid dashed line	Faint dotted line

2. Constructing Points

Once the axes are defined, the dockable panel (right side by default) becomes active:

Enter the Y offset (metres along the Y-axis from origin).
Enter the X offset (metres along the X-axis from origin).
Click Construct Point (or press Enter).

The plugin places a red × marker at the computed map position and draws:

A blue dashed line from the origin along the Y-axis to the projection point.
A green dashed line from the projection point perpendicular to the constructed point.
A small white □ at the right-angle corner.
A compact label showing the offset values.

You can construct as many points as you need. Each point is added to the results table in the panel.

3. Exporting Points

Click Export to Layer to create a temporary memory layer named “Orthogonal Measure Points” containing all constructed points:

Field	Type	Description
`id`	Integer	Sequential point number
`x_offset`	Double	X offset in metres
`y_offset`	Double	Y offset in metres
`map_e`	Double	Easting in map CRS
`map_n`	Double	Northing in map CRS

The layer uses the current project CRS and can be saved to any spatial format (Shapefile, GeoPackage, etc.) using standard QGIS tools.

User Interface

Toolbar & Menu

Toolbar icon: Click the Orthogonal Measure icon, or go to Plugins → Orthogonal Measure.
The map tool activates, and the dockable panel opens.

Dockable Panel

The panel can be:

Docked to the left, right, top, or bottom of the QGIS window.
Tabbed alongside Layers, Browser, or any other panel.
Floated as an independent window.

Section	Description
Status	Instructions and status messages; shows origin and Y-axis coords once defined.
Enter offset (m)	Y and X spinboxes (range ±999 999 m, 3 decimal places, 0.1 m step).
Constructed Points	Table listing all constructed points with offsets and map coordinates.
Buttons	Reset — clear everything. Export to Layer — export points.

Keyboard Shortcuts

Key	Action
`Enter`	Construct point (when a spinbox is focused)
`Escape`	Reset the tool (clear axes and all points on the canvas)

Snapping

When the map tool is active, vertex + segment snapping is automatically enabled on all layers with a 20 px tolerance. This lets you precisely snap the origin or Y-axis point to existing features. The previous snapping configuration is restored when the tool is deactivated.

Visual Feedback

All visual elements are drawn directly on the map canvas and automatically reposition when you pan or zoom.

Element	Appearance
Origin marker	Red double-triangle, 12 px
Y-axis point marker	Blue triangle, 10 px
Y-axis (positive)	Blue dashed, 2 px
Y-axis (negative)	Blue dotted, 1 px, faded
X-axis (positive)	Green dashed, 2 px
X-axis (negative)	Green dotted, 1 px, faded
Constructed point	Red ×, 12 px
Y projection line	Blue dashed, origin → projection
X projection line	Green dashed, projection → point
Right-angle indicator	White □, 6 px at the corner
Offset label	Compact text, white background, thin border

Typical Workflow

 1.  Open your project in QGIS (any CRS).
 2.  Click the Orthogonal Measure toolbar icon.
 3.  Click on a known point on the map → origin is set (red marker).
 4.  Click a second point that defines the Y-direction (blue marker).
     → Axes appear on the canvas; the panel becomes active.
 5.  Enter Y = 10.000, X = 0.000 → click Construct Point.
     → A point is placed 10 m along the Y-axis.
 6.  Enter Y = 5.000, X = -3.500 → click Construct Point.
     → A point is placed 5 m along Y and 3.5 m to the left of Y.
 7.  Repeat for all needed points.
 8.  Click Export to Layer → memory layer is added to the project.
 9.  Right-click the layer → Export → Save As… to save permanently.
10.  Close the panel or press Reset to start a new measurement.

Technical Details

CRS handling: Offsets are in ground metres. The plugin uses QgsDistanceArea with the project ellipsoid to convert between map-CRS units and ground distances, so it works accurately in EPSG:3857, UTM zones, state planes, and even geographic CRS.
Axis vectors: Internally computed as unit vectors scaled so that 1.0 = 1 ground metre. The X-axis is the Y-axis rotated 90° clockwise: (a, b) → (b, -a).
Canvas items: All markers, rubber bands, and labels are QgsMapCanvasItem objects that reposition on pan/zoom. Labels use a fixed pixel size for consistent readability.
Memory layer export: Uses the QGIS memory provider ("memory"). The layer inherits the project CRS.

Installation

From ZIP

Download the plugin ZIP archive.
In QGIS, go to Plugins → Manage and Install Plugins → Install from ZIP.
Select the ZIP file and click Install.

Manual

Copy the orthogonal_measure folder to your QGIS plugins directory:
- Windows: %APPDATA%\QGIS\QGIS3\profiles\default\python\plugins\
- Linux: ~/.local/share/QGIS/QGIS3/profiles/default/python/plugins/
- macOS: ~/Library/Application Support/QGIS/QGIS3/profiles/default/python/plugins/
Restart QGIS (or reload plugins).
Enable Orthogonal Measure in Plugins → Manage and Install Plugins.

File Structure

orthogonal_measure/
├── __init__.py                        # Plugin entry point (classFactory)
├── orthogonal_measure.py              # Main plugin class (OrthogonalMeasure)
├── ortho_map_tool.py                  # Map tool + canvas items
├── orthogonal_measure_dialog.py       # Dockable panel (QDockWidget)
├── orthogonal_measure_dialog_base.ui  # Qt Designer UI form
├── resources.py                       # Compiled Qt resources (icon)
├── resources.qrc                      # Qt resource definition
├── metadata.txt                       # QGIS plugin metadata
├── icon.png                           # Plugin icon
├── README.md                          # Markdown documentation
├── README.html                        # This file
└── i18n/                              # Translations

Known Limitations

The export creates a temporary memory layer — it must be saved manually to persist.
The plugin does not support entering offsets in units other than metres.
Axis lines have a fixed visual length (1.5× the distance between origin and Y-axis point).