๐งญ Plotter Widget - User Guide
The Plotter Widget is a PyQt5-based graphical interface integrated into QGIS that enables users to plot calculated points like cut points, offset points, and extended points along a selected line feature. ๐ฏ This tool is especially valuable for precision mapping and SVAMITVA survey workflows requiring accurate line-based geometry operations.
๐ง Key Featuresโ
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๐ Unit Conversion
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Meters
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Metric Links (1 = 0.2 meters)
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Gunterโs Links (1 = 0.201168 meters)
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๐ Base Point Selection
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Start Point
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End Point
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๐ Point Types
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Cut Point: At a given length along the line.
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Offset Point: Perpendicular to the line at a given distance.
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Extended Point: When the length exceeds the original line.
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๐๏ธ Memory Layer Integration
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Outputs are saved as a new memory layer.
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Works with both single-part and multi-part lines.
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๐จ Categorized Symbology
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Green: Start Point
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Red: End Point
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Orange: Cut Point
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Blue: Offset Point
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Purple: Extended Point
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๐ก๏ธ Robust Error Handling
- Clear messages guide users to correct inputs.
๐ How to Use the Plotter Widgetโ
๐ช Step 1: Launch the Widgetโ
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Open QGIS.
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From the plugin menu or the custom GUI, open Plotter Widget.
๐ Step 2: Select a Line Featureโ
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Activate a line layer from the Layers panel.
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Select exactly one line feature.
โน๏ธ Supports both single and multi-part geometries.
๐ ๏ธ Step 3: Configure Inputsโ
๐ฃ a. Unitsโ
Choose from:
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Meters
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Metric Links
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Gunterโs Links
๐งญ b. Choose Base Pointโ
Select whether to start from the:
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Start Point
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End Point
โ๏ธ c. Cut Lengthโ
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Enter the distance for the cut point.
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Negative value โ Extends the line backward.
โ๏ธ d. Offset Lengthโ
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Enter perpendicular offset distance.
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Positive โ Right of line.
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Negative โ Left of line.
๐งฉ Step 4: Plot Pointsโ
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Click Plot โถ๏ธ
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The tool generates:
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โ Cut Point
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๐ต Offset Point
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๐ฃ Extended Point (if applicable)
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They are added to a new memory layer: "Plotted Points".
๐บ๏ธ Step 5: Visualize Resultsโ
๐๏ธ Symbology Keyโ
Color | Point Type |
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๐ข Green | Start Point |
๐ด Red | End Point |
๐ Orange | Cut Point |
๐ต Blue | Offset Point |
๐ฃ Purple | Extended Point |
You can rerun the widget with new values as needed.
โ ๏ธ Error Messages & Troubleshootingโ
โ Error Message | ๐ก Cause | โ Solution |
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"Please select a layer." | No layer selected | Select a line layer in QGIS. |
"Selected layer is not a line layer." | Wrong geometry type | Use a valid line geometry layer. |
"Select exactly one line feature." | 0 or multiple features selected | Select one valid line feature. |
"Feature has no geometry." | Geometry is missing | Choose a feature with valid lines. |
"Cut point calculation failed." | Input error or geometry problem | Check values and retry. |
๐ Best Practicesโ
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โ๏ธ Always validate your selected feature before plotting.
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๐ Use correct units based on your CRS and survey standards.
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๐งฉ Understand the behavior with multi-part lines.
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๐พ Save the memory layer if needed for further analysis.
๐ Example Use Caseโ
๐บ๏ธ Scenario: You want to place a cut point 50m from the start of a road, then offset it 10m right for boundary marking.
Input | Value |
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Units | Meters |
Base Point | Start |
Cut Length | 50 |
Offset Length | 10 |
๐งฎ Result:
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A cut point at 50m
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An offset point 10m to the right
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Layer: "Plotted Points"
๐ง Advanced Tipsโ
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โ Use negative cut lengths to extend backwards.
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๐งผ The layer is always reset to prevent duplicates.
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๐ Reuse for multiple segments โ each run updates the points cleanly.
๐ The Plotter Widget empowers SVAMITVA workflows and survey operations with high precision and ease. Whether you're mapping cadastral plots or engineering offsets, this tool ensures spatial accuracy every step of the way. ๐บ๏ธ๐