Diagram Quality Spike: Ground Truth vs Generated

3 HKDSE past paper diagrams compared against AI-generated SVG and TikZ versions. Actual exam figures shown as ground truth—judge for yourself.

Test 1: Regular Tetrahedron

2012 Q40 · figureType: regular-tetrahedron · 4 vertices + 1 auxiliary
DiagramSpec
Vertices: A, B, C, D
Auxiliary: E (foot of perp from A to BC)
Angles: theta = angle AED
Lengths: side = 2x, EC = x
Constraints: all edges equal; E is midpoint of BC
Ground Truth (Past Paper)

HKEAA 2012 P2 Q40

2012 Q40 original diagram
Generated SVG

LLM → SVG Direct

θ 2x A B C D E
Generated TikZ

LLM → TikZ → SVG

µ2xABCDE
What to compare: Vertex placement (A top, B/D sides, C bottom in original). Dashed vs solid edges. Perspective/projection angle. Internal construction lines. The original shows no angle arc or E label—those are added by the student.

Test 2: Rectangular Box

2016 Q39 · figureType: rectangular-box · 8 vertices + 2 auxiliary
DiagramSpec
Vertices: A-H (full box)
Auxiliary: P (midpoint AC), Q (on GH)
Angles: angle PFQ
Lengths: AB=16, BC=12, h=15, HQ=15, QG=9
Constraints: rectangular box
Ground Truth (BrightMind)

BrightMind Solution 2016 Q39

2016 Q39 original diagram
Generated SVG

LLM → SVG Direct

∠PFQ 16 cm 12 cm 15 cm A B C D E F G H P Q
Generated TikZ

LLM → TikZ → SVG

161215ABCDEFGHPQ
What to compare: Vertex labeling convention (ABCD bottom, EFGH top). Right angle marks at corners. Dimension label placement. Construction lines for PF, PQ, FQ. Depth cues (which edges dashed). The original includes right-angle marks at every corner—neither generated version does.

Test 3: Perpendicular to Plane

2014 Q40 · figureType: perpendicular-to-plane · 4 vertices + 1 auxiliary
DiagramSpec
Vertices: A, B, C, D
Auxiliary: E (foot of perp from A to CD)
Angles: theta = angle AEB
Lengths: BC=8, BD=15, CD=17, AB=8
Constraints: AB perp plane BCD; angle BCD = 90 deg
Ground Truth (Past Paper)

HKEAA 2014 P2 Q40

2014 Q40 original diagram
Generated SVG

LLM → SVG Direct

θ 8 15 17 8 ⊥ plane A B C D E
Generated TikZ

LLM → TikZ → SVG

µ815178ABCDE
What to compare: Vertical pole AB clearly distinct from ground plane BCD. Dashed line for CD (ground edge behind pole). Dimension labels (8m, 15m, 17m) placement. Ground plane perspective. The original uses dotted lines for CD; the generated versions use different dashing.

Observations

Ground Truth (Past Paper)

  • Clean, minimal line work—no color, no fills
  • Consistent dashed lines for hidden/distant edges
  • Right angle marks where needed
  • Dimension labels placed close to edges
  • No angle arcs drawn—students construct those
  • Oblique projection with consistent depth cues

Generated SVG

  • Full control over layout, color coding, labels
  • Larger output, clearer labels
  • Zero dependencies
  • Adds angle arcs and auxiliary point markers (not in original)
  • Uses system fonts (Times New Roman), Greek via Unicode
  • Pipeline: LLM generates SVG directly from diagramSpec

Generated TikZ

  • LaTeX-quality typography (Computer Modern)
  • Proper math symbols (but theta renders as μ due to font encoding)
  • Academic-grade appearance
  • Smaller output (needs scaling)
  • Single-threaded rendering via node-tikzjax
  • Pipeline: LLM generates TikZ → node-tikzjax renders to SVG

Verdict

With ground truth side-by-side, the gaps are visible. Both generated versions capture the geometric structure correctly, but differ from the original in projection angle, label conventions, and styling details. The original past paper diagrams are minimal (black lines, no color, no fills)—our generated versions add color coding and auxiliary markers that weren't in the exam.

Key differences to address: (1) Right angle marks are missing in generated versions. (2) Vertex labeling orientation differs (2012: original has B left/D right; generated has B left/C right). (3) TikZ theta symbol renders as μ due to cmmi10 font encoding. (4) Ground truth uses dotted/dashed lines more consistently for depth. (5) Angle arcs are added by generated versions but absent from the originals.

Recommendation remains: Start with SVG for speed, but calibrate the styling to match the past paper aesthetic—black lines, no color fills, consistent dashing, right angle marks. The generated geometry is sound; the presentation needs to match what teachers and students expect to see.

Generated 2026-02-24 · TalentCoop R&D · 3 test cases, 9 diagrams (3 ground truth + 3 SVG + 3 TikZ)