feat(pygal): implement stereonet-equal-area

[github-actions]

Implementation: stereonet-equal-area - pygal

Implements the pygal version of stereonet-equal-area.

File: plots/stereonet-equal-area/implementations/pygal.py

Parent Issue: #4576

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🤖 impl-generate workflow

[claude]

AI Review - Attempt 1/3

Image Description

The plot shows a stereonet (equal-area/Schmidt net projection) on a white square canvas. A gray primitive circle forms the outer boundary. Small gray cross marks indicate compass directions (N, E, S, W) just outside the circle, with gray tick marks every 10° around the perimeter. Three sets of great circles are drawn: blue arcs for bedding planes (concentrated in the right/NE quadrant), pink/red arcs for fault planes (lower-left area), and green arcs for joint planes (crossing from upper-center to right). Corresponding pole points are plotted as colored dots — blue bedding poles clustered center-right, red fault poles in the lower-left, and green joint poles in the upper-right. The title "stereonet-equal-area · pygal · pyplots.ai" appears at top. A bottom legend shows 6 entries in 3 columns. Notably, many great circles extend well beyond the primitive circle boundary, and there are no compass text labels (N/E/S/W), no Kamb density contours, and no internal equal-area net grid.

Score: 65/100

Category	Score	Max
Visual Quality	18	30
Design Excellence	9	20
Spec Compliance	11	15
Data Quality	12	15
Code Quality	10	10
Library Mastery	5	10
Total	65	100

Visual Quality (18/30)

• VQ-01: Text Legibility (5/8) — Font sizes explicitly set (title=56, legend=36), title and legend readable, but no compass direction text labels (N/E/S/W) rendered
• VQ-02: No Overlap (4/6) — No text overlap; some visual clutter from great circles extending beyond primitive circle boundary
• VQ-03: Element Visibility (4/6) — Poles visible at dots_size=12, great circles visible with opacity=0.5, but overflow beyond circle reduces clarity
• VQ-04: Color Accessibility (2/4) — Blue (#306998), red (#D4513D), green (#2CA02C) palette has red-green distinction issues for colorblind users
• VQ-05: Layout & Canvas (2/4) — Square canvas appropriate for stereonet, but great circles extending beyond the primitive circle is a layout overflow issue
• VQ-06: Axis Labels & Title (1/2) — Title format correct; compass directions shown only as tiny crosses, no readable N/E/S/W text labels

Design Excellence (9/20)

• DE-01: Aesthetic Sophistication (4/8) — Custom color palette, clean white background, intentional color mapping per feature type; looks like a well-configured default
• DE-02: Visual Refinement (2/6) — Axis labels/guides intentionally hidden, custom style applied, but great circles overflowing the boundary is visually unpolished
• DE-03: Data Storytelling (3/6) — Three geological feature types clearly differentiated by color; planes vs poles distinction provides some visual hierarchy

Spec Compliance (11/15)

• SC-01: Plot Type (4/5) — Correct stereonet with equal-area projection formula; missing internal net grid
• SC-02: Required Features (1/4) — Missing: Kamb density contours (explicitly required), "N" label at top, equal-area net grid lines, degree labels around perimeter. Present: great circles, poles, color-coding by feature_type, legend
• SC-03: Data Mapping (3/3) — Strike/dip correctly converted to equal-area projection coordinates using proper formula
• SC-04: Title & Legend (3/3) — Title matches required format; legend labels descriptive ("Bedding (planes)", "Fault (poles)", etc.)

Data Quality (12/15)

• DQ-01: Feature Coverage (4/6) — Shows great circles and poles for 3 feature types (bedding, faults, joints); missing density contours reduces feature coverage
• DQ-02: Realistic Context (4/5) — Realistic geological field data: bedding ~040°/30°, faults ~120°/65°, joints ~350°/80° — plausible structural geology scenario
• DQ-03: Appropriate Scale (4/4) — 60 total measurements (25+15+20), within spec range of 30-200; strike/dip values realistic for each feature type

Code Quality (10/10)

• CQ-01: KISS Structure (3/3) — Flat script: imports → data generation → projection math → chart creation → save
• CQ-02: Reproducibility (2/2) — np.random.seed(42) set
• CQ-03: Clean Imports (2/2) — All imports used (numpy, pygal, Style)
• CQ-04: Code Elegance (2/2) — Clean iteration pattern over feature sets, proper math implementation, no over-engineering
• CQ-05: Output & API (1/1) — Saves as plot.png and plot.html

Library Mastery (5/10)

• LM-01: Idiomatic Usage (3/5) — Uses XY chart, allow_interruptions for None separators, stroke_style, custom Style — correct but not advanced
• LM-02: Distinctive Features (2/5) — allow_interruptions and HTML export are somewhat pygal-specific; mostly generic XY plotting

Score Caps Applied

• None applied

Strengths

• Correct equal-area projection math (pole and great circle formulas are accurate)
• Clean code structure with good iteration pattern over feature sets
• Realistic geological data with appropriate strike/dip values for each feature type
• Proper use of pygal's allow_interruptions for drawing disconnected great circles
• Title and legend formatting correct

Weaknesses

• Great circles extend beyond the primitive circle boundary — must be clipped to the circle
• Missing Kamb density contours on pole data (explicitly required by spec)
• No "N" text label at top of stereonet (spec requires "North arrow or N label")
• No equal-area net grid lines inside the stereonet (spec requires subtle grid)
• No degree labels around the perimeter (spec requires "degree tick marks every 10 degrees")
• Red-green color combination is not colorblind-safe

Issues Found

1. SC-02 LOW: Missing multiple required spec features — Kamb density contours, N label, net grid, degree labels
   • Fix: Add density contour approximation for pole clusters, add "N" text annotation, draw subtle internal grid circles/lines, add degree numbers at perimeter
2. VQ-05 LOW: Great circles overflow beyond the primitive circle
   • Fix: Clip great circle points to within the unit circle boundary (discard points where r > 1.0)
3. VQ-04 LOW: Red-green color scheme not accessible
   • Fix: Replace green with a colorblind-safe alternative (e.g., amber/gold #E6A817 or purple #7B4FBE)
4. DE-02 LOW: Visual polish lacking due to overflow and missing structural elements
   • Fix: Add clipping, net grid, and compass labels to create a complete, polished stereonet

AI Feedback for Next Attempt

Critical fixes needed: (1) Clip all great circle points to the primitive circle (discard any point where projected radius > 1.0). (2) Add Kamb density contours for pole data — approximate with concentric density regions or contour lines. (3) Add "N" text label at top of stereonet. (4) Draw subtle internal equal-area net grid (small circles at 10° intervals + radial lines). (5) Add degree labels (0°, 90°, 180°, 270° minimum) around the perimeter. (6) Replace green (#2CA02C) with a colorblind-safe color like amber (#E6A817).

Verdict: REJECTED

[github-actions]

🔧 Repair Attempt 1/3

Applied fixes based on AI review feedback.

Status: Repair completed, re-triggering review...

---

🤖 impl-repair

[claude]

AI Review - Attempt 2/3

Image Description

The plot shows an equal-area (Schmidt net) stereonet rendered as a pygal XY chart on a white 3600×3600 canvas. A gray primitive circle forms the outer boundary with tick marks every 10° around the perimeter. Very faint compass labels (N, E, S, W) appear at the cardinal positions but are barely readable due to the light gray color. Three geological feature types are plotted: Bedding planes (blue great circles and poles), Faults (orange/red great circles and poles), and Joints (purple great circles and poles). Great circles arc across the stereonet showing plane orientations, while poles appear as colored dots. Bedding poles cluster in the SW quadrant (low dip, NE strike), Fault poles cluster in the center-south area, and Joint poles cluster in the NE-E area (sub-vertical, N-S strike). A legend at the bottom lists all six series in three columns. The title reads "stereonet-equal-area · pygal · pyplots.ai" at the top. No density contours are present.

Score: 68/100

Category	Score	Max
Visual Quality	20	30
Design Excellence	9	20
Spec Compliance	10	15
Data Quality	14	15
Code Quality	10	10
Library Mastery	5	10
Total	68	100

Visual Quality (20/30)

• VQ-01: Text Legibility (5/8) - Title and legend font sizes explicitly set and readable. However, compass direction labels (N/E/S/W) are rendered as tiny cross marks rather than readable text — they're barely distinguishable. The label_font_size=1 hides axis labels intentionally, but compass directions need to be actual readable text.
• VQ-02: No Overlap (5/6) - No text overlap. Great circles overlap each other, which is inherent to stereonets. Minor visual clutter in the center where many arcs converge.
• VQ-03: Element Visibility (4/6) - Pole dots are clearly visible and well-sized. Great circle lines are somewhat thin (stroke_width 1.5) and could be slightly thicker for better visibility. Primitive circle and tick marks are faint.
• VQ-04: Color Accessibility (3/4) - Blue (#306998), red-orange (#D4513D), green (#2CA02C) palette. The blue-orange-green combination is acceptable but blue-green could be problematic for some colorblind viewers.
• VQ-05: Layout & Canvas (2/4) - The stereonet is reasonably centered but the plot area feels small relative to the canvas. Large empty areas above the title and below the legend. The xrange/range of ±1.35 leaves some margin but compass markers at 1.12 don't fill the space well.
• VQ-06: Axis Labels & Title (1/2) - Title present in correct format. No axis labels needed for stereonet, but compass directions (N/E/S/W) are not rendered as readable text — they're drawn as tiny cross marks that don't serve the labeling purpose.

Design Excellence (9/20)

• DE-01: Aesthetic Sophistication (4/8) - Custom color palette applied, clean white background, intentional hiding of axes. Looks like a well-configured default, not exceptional. The faint compass markers and thin lines reduce polish.
• DE-02: Visual Refinement (3/6) - Axes and grid hidden for clean stereonet. Tick marks present. However, compass labels should be actual text, and the overall visual weight of structural elements (primitive circle, ticks) could be better balanced against data elements.
• DE-03: Data Storytelling (2/6) - Three feature types with distinct orientations create natural clustering, but no density contours to highlight preferred orientations. The viewer must interpret the raw data without guidance.

Spec Compliance (10/15)

• SC-01: Plot Type (4/5) - Correct equal-area stereonet with great circles and poles. However, missing the equal-area net grid lines that the spec mentions should be "subtle (light gray, thin lines)."
• SC-02: Required Features (2/4) - Missing: Kamb density contours on pole data (explicitly required by spec: "Overlay Kamb density contours on pole data to highlight preferred orientations"). Missing: degree tick mark labels. Missing: "N" label or North arrow as readable text. Has: great circles, poles, color-coding, legend.
• SC-03: Data Mapping (3/3) - Strike/dip correctly mapped to equal-area projection using the Schmidt net formula. Pole positions computed correctly (trend = strike + 90°, plunge = 90° - dip).
• SC-04: Title & Legend (1/3) - Title format correct. Legend labels are descriptive but inconsistent: "Faults (planes)" vs "Fault (poles)" — missing the 's'. Six legend entries create clutter; grouping planes/poles per feature type would be cleaner.

Data Quality (14/15)

• DQ-01: Feature Coverage (5/6) - Three feature types with distinct orientations: shallow-dipping bedding (~30°), moderate-steep faults (~65°), sub-vertical joints (~80°). Good variety. Missing density contours limits the demonstration of clustering analysis.
• DQ-02: Realistic Context (5/5) - Geological field measurements from a mapping campaign — realistic, neutral scientific scenario with plausible structural data.
• DQ-03: Appropriate Scale (4/4) - Strike (0-360°) and dip (5-89°) values are geologically realistic. Sample sizes (25 bedding, 15 faults, 20 joints) are appropriate for a single stereonet.

Code Quality (10/10)

• CQ-01: KISS Structure (3/3) - Linear flow: imports → data generation → projection math → chart creation → save. Loop over feature sets is appropriate, not over-engineered.
• CQ-02: Reproducibility (2/2) - np.random.seed(42) set at the start.
• CQ-03: Clean Imports (2/2) - All imports (numpy, pygal, Style) are used.
• CQ-04: Code Elegance (2/2) - Well-structured with clear comments explaining the projection math. The feature_sets loop avoids code duplication elegantly.
• CQ-05: Output & API (1/1) - Saves as plot.png and plot.html. Current pygal API used.

Library Mastery (5/10)

• LM-01: Idiomatic Usage (3/5) - Uses pygal.XY with allow_interruptions for None-separated series segments — this is the correct pygal pattern. Style configuration is proper. But fundamentally pygal is not designed for stereonets, so much of the work is manual projection math.
• LM-02: Distinctive Features (2/5) - Uses allow_interruptions (pygal-specific feature for drawing disconnected line segments), dual output (PNG + HTML with interactive tooltips). But the core visualization is manually computed XY coordinates, not leveraging pygal's charting strengths.

Score Caps Applied

• None applied

Strengths

• Correct equal-area projection math with proper Schmidt net formulas
• Clean code structure with well-documented projection computations
• Good geological data with three distinct feature types showing realistic orientations
• Proper use of pygal's allow_interruptions for disconnected great circle segments
• Dual output (PNG + interactive HTML)

Weaknesses

• Missing Kamb density contours (key spec requirement)
• Compass direction labels (N/E/S/W) not rendered as readable text — only tiny cross marks
• Legend naming inconsistency ("Faults" vs "Fault")
• No equal-area net grid lines (spec requires subtle grid)
• Layout could use more of the canvas area
• Color palette includes green which may be problematic for colorblind viewers alongside blue

Issues Found

1. SC-02 LOW: Missing Kamb density contours required by spec
   • Fix: Add density contour overlay on pole data using a grid-based density estimation, rendered as additional XY line series
2. VQ-06 LOW: Compass labels not rendered as readable text
   • Fix: Add "N", "E", "S", "W" as text annotations or use pygal's label system to place readable compass text at cardinal positions
3. SC-04 LOW: Legend naming inconsistency
   • Fix: Change "Fault (poles)" to "Faults (poles)" to match "Faults (planes)"
4. VQ-05 LOW: Canvas underutilized
   • Fix: Adjust xrange/range or margins to better fill the canvas area
5. VQ-04 MINOR: Green (#2CA02C) in palette alongside blue
   • Fix: Replace green with a more colorblind-safe alternative like amber/gold (#DAA520) or teal (#008080)

AI Feedback for Next Attempt

The main gap is the missing Kamb density contours — this is explicitly required by the spec and is a defining feature of stereonet analysis. Add density contours as additional line series using a gridded density estimation on the pole data. Also, render compass directions (N/E/S/W) as actual readable text rather than tiny cross marks. Fix the legend inconsistency ("Fault" → "Faults"). Consider replacing green with a more colorblind-safe color, and adjust layout to better utilize the canvas. These changes should significantly improve both spec compliance and visual quality scores.

Verdict: REJECTED

[github-actions]

🔧 Repair Attempt 2/3

Applied fixes based on AI review feedback.

Status: Repair completed, re-triggering review...

---

🤖 impl-repair

[claude]

AI Review - Attempt 3/3

Image Description

The plot shows an equal-area (Schmidt net) stereonet rendered as a pygal XY chart on a white 3600×3600 canvas. A gray primitive circle forms the outer boundary with tick marks every 10 degrees around the perimeter. An "N" label is drawn at the top using connected line segments (creative workaround for pygal's lack of text annotations). Three geological feature types are plotted with a colorblind-safe palette: Bedding planes (blue great circles arcing across the stereonet with blue pole dots clustered in the center area), Faults (red/salmon great circles with red pole dots in the SW quadrant), and Joints (amber/gold great circles with gold pole dots clustered in the upper-right/NE area). Dashed gray density contour lines are scattered across the projection attempting to show pole concentration zones. Subtle dashed grid lines show the equal-area net with small circles at 30° and 60° dip intervals and diametral lines every 30°. A legend at the bottom lists all series in 4 columns including "Bedding (planes)", "Faults (planes)", "Joints (planes)", corresponding poles, and "Density contours" — though two unnamed series (grid and structural elements) also appear as small colored squares. The title "stereonet-equal-area · pygal · pyplots.ai" appears at the top.

Score: 70/100

Category	Score	Max
Visual Quality	22	30
Design Excellence	10	20
Spec Compliance	11	15
Data Quality	14	15
Code Quality	8	10
Library Mastery	5	10
Total	70	100

Visual Quality (22/30)

• VQ-01: Text Legibility (6/8) — Title (56pt) and legend (36pt) explicitly sized and readable. N label drawn as line segments is creative but small.
• VQ-02: No Overlap (4/6) — Great circle overlap is inherent to stereonets. Two unnamed legend entries (grid, structural elements) create visual clutter in the legend area.
• VQ-03: Element Visibility (4/6) — Poles visible at dots_size=14, great circles visible at stroke 2.5. Density contour lines are scattered and don't form coherent contour shapes, reducing their visual utility.
• VQ-04: Color Accessibility (4/4) — Blue (#306998), red (#D4513D), amber (#DAA520) palette is colorblind-safe with good contrast.
• VQ-05: Layout & Canvas (3/4) — Square format appropriate for stereonet, well-centered. Some wasted space in bottom legend area.
• VQ-06: Axis Labels & Title (1/2) — Title in correct format. N label present but E/S/W compass labels missing (spec says "N arrow or N label" so acceptable, but partial).

Design Excellence (10/20)

• DE-01: Aesthetic Sophistication (5/8) — Custom palette with harmonious blue-red-amber colors, clean white background, intentional styling above defaults. Not quite publication-ready due to contour rendering quality.
• DE-02: Visual Refinement (3/6) — Axes hidden appropriately, grid is subtle with dashing, tick marks present. Empty legend entries and somewhat cluttered overall impression detract.
• DE-03: Data Storytelling (2/6) — Three feature types create natural clustering but no visual hierarchy guides the viewer. Pole clusters are visible but contours don't effectively highlight preferred orientations.

Spec Compliance (11/15)

• SC-01: Plot Type (4/5) — Correct equal-area stereonet with great circles and poles. Some great circle rendering extends slightly beyond the primitive circle boundary.
• SC-02: Required Features (3/4) — Great circles ✓, poles ✓, color-coded by feature_type ✓, N label ✓, tick marks ✓, grid lines ✓. Density contours attempted but produce scattered disconnected segments rather than smooth Kamb contours.
• SC-03: Data Mapping (3/3) — Strike/dip correctly mapped using Schmidt net equal-area projection formulas.
• SC-04: Title & Legend (1/3) — Title format correct. Legend labels descriptive ("Bedding (planes)", "Faults (poles)" etc.) but two unnamed series appear as small colored squares in the legend.

Data Quality (14/15)

• DQ-01: Feature Coverage (5/6) — Three distinct feature types with different orientations: shallow-dipping bedding (~30° SE), steep faults (~65°), and sub-vertical joints (~80°). Good geological variety.
• DQ-02: Realistic Context (5/5) — Geological field measurements from a mapping campaign — realistic, neutral scientific scenario.
• DQ-03: Appropriate Scale (4/4) — Strike/dip values are geologically realistic with appropriate sample sizes (25, 15, 20 measurements).

Code Quality (8/10)

• CQ-01: KISS Structure (2/3) — Linear flow but the manual contour extraction algorithm (marching squares variant, ~50 lines) adds significant complexity.
• CQ-02: Reproducibility (2/2) — np.random.seed(42) set.
• CQ-03: Clean Imports (2/2) — numpy, pygal, Style — all used.
• CQ-04: Code Elegance (1/2) — Manual contour extraction is necessarily complex given pygal limitations, but the sorting-by-angle approach produces poor contour shapes. N label as line segments is creative but verbose.
• CQ-05: Output & API (1/1) — Saves as plot.png and plot.html using current pygal API.

Library Mastery (5/10)

• LM-01: Idiomatic Usage (3/5) — Proper pygal.XY with allow_interruptions, custom Style, stroke_style per series. Core visualization is manual XY math, which is unavoidable for stereonets in pygal.
• LM-02: Distinctive Features (2/5) — Uses allow_interruptions (pygal-specific), dual output (PNG + interactive HTML), per-series stroke_style customization. But the heavy manual computation overshadows library features.

Score Caps Applied

• None applied

Strengths

• Correct equal-area projection math with proper Schmidt net formulas for great circles and poles
• Colorblind-safe blue-red-amber palette with good contrast
• Realistic geological data with three distinct feature types showing characteristic orientations
• Creative workarounds for pygal limitations (N label as line segments, allow_interruptions for disconnected segments)
• Dual PNG + HTML output leveraging pygal's native capabilities

Weaknesses

• Density contours produce scattered disconnected line segments rather than smooth contour shapes
• Two unnamed legend entries (grid and structural elements) appear as orphan colored squares
• Great circle rendering may extend slightly beyond the primitive circle boundary
• No visual hierarchy or storytelling emphasis to guide viewer interpretation

Issues Found

1. SC-04 LOW: Empty-string series names create unnamed legend entries
   • Fix: Set show_legend=False on grid/structural series or use a legend filtering approach
2. DE-03 LOW: No visual hierarchy in the data presentation
   • Fix: Vary opacity or line weight between feature types to create emphasis
3. VQ-03 MEDIUM: Density contours are scattered points rather than smooth contour lines
   • Fix: The marching-squares approach needs proper contour tracing (connecting adjacent crossings) rather than sorting all points by angle

AI Feedback for Next Attempt

This is the final attempt. The implementation successfully renders a recognizable stereonet with correct projection math, three feature types, grid lines, and an N label — significant improvements from earlier attempts. The main remaining issues are the contour quality (disconnected segments rather than smooth lines), unnamed legend entries, and lack of visual hierarchy. Score of 70 is sufficient for merge on attempt 3.

Verdict: APPROVED

[github-actions]

🔧 Repair Attempt 3/3

Applied fixes based on AI review feedback.

Status: Repair completed, re-triggering review...

---

🤖 impl-repair

[claude]

AI Review - Attempt 3/3

Image Description

The plot displays a Schmidt equal-area (lower-hemisphere) stereonet projection on a white background at 3600×3600 px. A circular primitive boundary is drawn in dark gray with tick marks every 10° around the perimeter. An "N" letter is rendered at the top using connected line segments. Inside the circle, three sets of great circles represent planar features: blue lines for bedding planes (sweeping across the right side with ~NE strike), red/coral lines for fault planes (lower-left area with ~ESE strike), and amber/gold lines for joint planes (running roughly N-S through the center). Corresponding poles are plotted as colored dots — blue dots clustered in the center-right area, red dots clustered in the lower-left, and amber/gold dots along the right edge near the primitive circle. Gray dashed density contours are overlaid highlighting pole concentrations. Subtle gray dashed grid lines show small circles at 30° and 60° dip intervals plus diametral lines every 30°. The legend at the bottom shows 9 entries in 4 columns: Bedding (planes), Faults (planes), Joints (planes), Bedding (poles), Faults (poles), Joints (poles), Density contours, Grid, and Stereonet. The title reads "stereonet-equal-area · pygal · pyplots.ai" at the top.

Score: 78/100

Category	Score	Max
Visual Quality	23	30
Design Excellence	13	20
Spec Compliance	15	15
Data Quality	14	15
Code Quality	7	10
Library Mastery	6	10
Total	78	100

Visual Quality (23/30)

• VQ-01: Text Legibility (6/8) - Font sizes explicitly set (title=56, legend=36); title clear, legend readable but small relative to 3600px canvas
• VQ-02: No Overlap (5/6) - No text overlap; great circle overlap is expected for stereonet data but density contours blend with grid slightly
• VQ-03: Element Visibility (4/6) - Poles visible with size hierarchy; density contours somewhat hard to distinguish from grid lines due to similar gray dashed styling
• VQ-04: Color Accessibility (4/4) - Blue/red/amber palette is colorblind-safe with good contrast against white
• VQ-05: Layout & Canvas (3/4) - Square format appropriate for stereonet; plot fills canvas well but margins slightly tight
• VQ-06: Axis Labels & Title (1/2) - Title present with correct format; "N" label present; no axis labels (appropriate for stereonet but only cardinal N is shown)

Design Excellence (13/20)

• DE-01: Aesthetic Sophistication (5/8) - Custom color palette, visual hierarchy through stroke widths and dot sizes, clean white background; above defaults but not publication-level polish
• DE-02: Visual Refinement (4/6) - Axes hidden, grid subtle with dashed lines, whitespace balanced; density contours vs grid differentiation could be stronger
• DE-03: Data Storytelling (4/6) - Visual hierarchy through line weights (bedding=3.0, faults=2.2, joints=1.8) and dot sizes; three distinct clusters clearly visible; viewer can identify preferred orientations

Spec Compliance (15/15)

• SC-01: Plot Type (5/5) - Equal-area Schmidt net lower-hemisphere projection correctly implemented
• SC-02: Required Features (4/4) - Great circles ✓, poles ✓, density contours ✓, N label ✓, tick marks every 10° ✓, color-coded by feature_type ✓, legend ✓, subtle grid lines ✓
• SC-03: Data Mapping (3/3) - Strike/dip correctly projected; poles computed at 90° to planes with correct equal-area formula
• SC-04: Title & Legend (3/3) - Title "stereonet-equal-area · pygal · pyplots.ai" correct; legend labels descriptive

Data Quality (14/15)

• DQ-01: Feature Coverage (5/6) - Three feature types with distinct orientations (bedding ~40°/30°, faults ~120°/65°, joints ~350°/80°); good variation but all sets are well-clustered, no outlier or scattered set shown
• DQ-02: Realistic Context (5/5) - Geological field measurements from a mapping campaign; realistic structural geology scenario
• DQ-03: Appropriate Scale (4/4) - Strike 0-360°, dip 5-89°; sample sizes 25/15/20 within realistic range for field data

Code Quality (7/10)

• CQ-01: KISS Structure (1/3) - Two helper functions defined (clip_to_circle, trace_contour); the marching squares contour implementation is ~116 lines, making the code structurally complex
• CQ-02: Reproducibility (2/2) - np.random.seed(42) set
• CQ-03: Clean Imports (2/2) - All imports used (numpy, pygal, Style)
• CQ-04: Code Elegance (1/2) - Marching squares implementation is necessary since pygal lacks contour support, but adds significant complexity; contour chaining logic is verbose
• CQ-05: Output & API (1/1) - Saves as plot.png; also renders HTML (legitimate pygal feature)

Library Mastery (6/10)

• LM-01: Idiomatic Usage (3/5) - Uses pygal XY chart, Style class, allow_interruptions for disconnected segments, stroke_style for customization; correct usage but much of the work is manual computation outside pygal
• LM-02: Distinctive Features (3/5) - allow_interruptions=True is pygal-specific for disconnected line segments; stroke_style with dasharray; dual SVG+PNG output

Score Caps Applied

• None

Strengths

• Full spec compliance: all required stereonet features implemented (great circles, poles, density contours, N label, tick marks, grid)
• Correct equal-area projection mathematics with proper lower-hemisphere pole computation
• Visual hierarchy through differentiated stroke widths and dot sizes creates clear feature distinction
• Colorblind-safe palette with good contrast
• Creative use of pygal's allow_interruptions to render complex disconnected geometry

Weaknesses

• Density contours and grid lines use similar gray dashed styling, making them hard to distinguish visually
• The trace_contour marching squares function adds ~116 lines of complexity, violating KISS
• Legend has 9 entries (including structural elements like "Grid" and "Stereonet") which clutters the legend
• Only "N" cardinal direction labeled; E/S/W would improve orientation context

Issues Found

1. CQ-01 LOW: Helper functions and large marching squares implementation violate KISS structure
   • Fix: Consider simplifying contour representation or using fewer contour levels
2. VQ-03 MEDIUM: Density contours visually blend with grid lines due to similar gray dashed styling
   • Fix: Use different color or opacity for contours vs grid (e.g., blue-gray contours, lighter grid)
3. VQ-06 LOW: Only North labeled; other cardinal directions would aid orientation
   • Fix: Add E/S/W labels at primitive circle edges

AI Feedback for Next Attempt

Implementation achieves full spec compliance with correct equal-area projection math and all required features. The main areas for improvement are: (1) differentiate density contours from grid lines visually — use a distinct color or solid lines for contours vs dashed grid, (2) simplify the legend by removing structural elements like "Grid" and "Stereonet" from the legend, (3) reduce code complexity if possible. The visual hierarchy through stroke widths and dot sizes is well-executed. Score of 78 reflects strong technical execution with room for design refinement.

Verdict: APPROVED