Advanced Profile Tool — User Guide

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1. Overview

The Advanced Profile Tool generates cross-sections and long sections along a selected alignment, samples elevations from one or more DEM rasters, plots the resulting profiles, compares surfaces (cut/fill), and computes earthworks volumes. Results can be exported to GeoPackage, CSV, DXF and image/PDF formats. Three algorithms are also registered in the Processing Toolbox under Advanced Profile Tool → Profiles for scripted and batch use.

2. Workflow

The dialog follows the run sequence from left to right:

1. Alignment — choose the line layer and feature(s) that define the route.
2. Section Layout — set interval, widths, tangent method, labelling and chainage limits.
3. DEM Surfaces — add the rasters to sample, with per-surface band, interpolation, vertical offset and style.
4. Generate — build the section lines and sample all enabled surfaces.
5. Viewer — step through the profiles, adjust vertical exaggeration, inspect elevations.
6. Comparison / Volumes — difference two surfaces, review cut/fill areas per section and volumes between sections.
7. Outputs — export layers, tables, plots and drawings.

3. Tab reference

3.1 Alignment

• Select the alignment layer and either the selected features or a single picked feature.
• The layer must be in (or be assigned) a projected CRS; distances are computed in the layer's linear units. Geographic (degree) CRSs are rejected — see Troubleshooting.
• Multipart lines are joined end-to-end where parts touch within a small tolerance; parts that cannot be joined are treated as separate alignments. A reject option is available where multipart input indicates a data problem.
• The direction of increasing chainage follows the digitised direction; a reverse option flips it. A start chainage offset sets the displayed chainage at the alignment start (for example 1+000 rather than 0+000).

3.2 Section Layout

• Interval mode: sections at a regular chainage interval (default 20 m), by count, or from an explicit chainage list. Alignment endpoints can be included or excluded, and vertex chainages added.
• Widths: left and right widths (default 25 m each) measured perpendicular to the alignment.
• Tangent method: local uses the segment direction at the chainage; averaged and smoothed blend directions over a distance to reduce fanning and crossing of sections at sharp bends.
• Labelling: label format (default {prefix}{number} {chainage}), prefix, numbering, and the major-section frequency (every 5th by default). Major sections draw with a heavier style.

3.3 DEM Surfaces

• Add any number of raster surfaces; each has its own band, interpolation method, vertical offset (datum adjustment), colour and line style, and can be toggled on or off.
• One surface is nominated the reference for comparisons and volumes.
• The sampling interval defaults to half the finest DEM pixel size; it can be set manually.

3.4 Generate

• Runs the section generation and DEM sampling as a background task with progress and cancellation.
• Warnings (intersecting sections, NoData gaps, clamped chainage limits) are listed on completion and logged to the AdvancedProfileTool message log.

3.5 Viewer

• Steps through sections (and the long section) with all enabled surfaces plotted against offset.
• Vertical exaggeration defaults to 10× and is adjustable; elevations, grid and cursor read-out honour the configured decimal places.

3.6 Comparison / Volumes

• Difference is computed as comparison − reference: fill where the comparison surface is above the reference, cut where below.
• Cut and fill areas per section are integrated by the trapezoidal rule with exact zero-crossing splits; NoData spans are excluded and reported as gap length.
• Volumes between consecutive sections use the average end area method (V = (A₁ + A₂)/2 × L), with a prismoidal option for higher accuracy where areas change rapidly between sections.

3.7 Outputs

• Section lines, profile points and result tables to a GeoPackage (default advanced_profile_outputs.gpkg), optionally in timestamped runs and per-run subfolders.
• Profile and comparison tables to CSV.
• Section plots to PNG/PDF at the configured page size (A3 landscape by default).
• Profiles to DXF (layers prefixed APT_) for CAD.

4. Chainage formats

Chainage entry fields accept any of the above forms, including negative chainages ahead of the datum.

5. Offset convention

Offsets are signed distances perpendicular to the alignment: negative to the left, positive to the right, when looking in the direction of increasing chainage. Section lines are written left end → centre → right end, so the geometric start of each section line is its left end. A display option shows unsigned offsets with L/R suffixes instead.

6. DEM interpolation and NoData

NoData handling: by default NoData samples remain as gaps in the profile (nothing is invented) and a warning reports the count. Optionally, gaps shorter than a maximum length (default 5 m) can be bridged by linear interpolation across the gap; longer gaps always remain open. Gap lengths are excluded from comparison areas and reported separately.

7. Volume method

Cross-section areas are converted to volumes between consecutive valid sections by the average end area method:

V = (A₁ + A₂) / 2 × L

where L is the chainage difference between the sections. Cut and fill are accumulated separately, with cumulative and net (mass-haul) totals reported. The prismoidal option applies the prismoidal correction where section shape changes significantly, which reduces the systematic overestimate of the average end area method on tapering earthworks. Sections invalidated by excessive NoData are skipped and the affected intervals flagged.

8. Export formats

9. Troubleshooting

"Calculation CRS is geographic (degree units)"

The alignment (or chosen calculation CRS) is in latitude/longitude, so distances would be computed in degrees. Reproject the alignment to a projected CRS (for example the local MGA/UTM zone) or select a projected calculation CRS. The plugin can suggest the UTM zone covering the layer extent.

Gaps in profiles (NoData)

Gaps indicate NoData cells or samples outside the DEM extent. Check raster coverage against the section extents and the declared NoData value. Enable gap interpolation only where short voids are acceptable to bridge; note that bridged spans are estimates, not measurements.

Intersecting section lines

On tight bends, adjacent perpendicular sections can cross within the section width, double-counting terrain in volume results. The generator reports intersecting pairs. Remedies: use the averaged or smoothed tangent method, reduce section widths, or increase the interval through the bend. Review flagged sections before relying on volumes.

No sections generated

Confirm the alignment feature is selected, the chainage window lies within the alignment length, and the interval is smaller than the alignment length. Warnings on the Generate tab identify rejected or clamped inputs.

10. Licence

Advanced Profile Tool — Copyright © 2026 Nikhil Jacob.

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the Licence, or (at your option) any later version. It is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for details.

Results depend on input data quality. Verify sampled surfaces, datums and volumes against survey control before using them for design or contractual quantities.