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True-color composite on Landsat TM — band-to-color-gun mapping?
likely airborne

Band Combination 3-2-1 on Landsat TM:

  • 🟥 R display gun ← Band 3 (Red)
  • 🟩 G display gun ← Band 2 (Green)
  • 🟦 B display gun ← Band 1 (Blue)

Each band feeds the matching color gun → image looks roughly natural.

⚠️ On Landsat 8/9 OLI (numbering shifted by 1 because coastal/aerosol = Band 1): - 🟥 R ← Band 4 (Red) - 🟩 G ← Band 3 (Green) - 🟦 B ← Band 2 (Blue)

💡

True color = 3-2-1 countdown (on TM). Each band matches its real color. OLI just shifts everything up by 1.

airborne/true-color-bands ✎ edit content

Photo scale formula for an aerial photograph?
likely airborne

Photo scale is just focal length divided by flying height.

  • Big focal length, low altitude → zoomed in, small ground area, lots of detail.
  • Small focal length, high altitude → wide view, big ground area, less detail.

Same trade-off as your phone camera — wide-angle covers more, telephoto zooms in. Aerial cameras are the same physics, just a few thousand feet up.

🔬 Science / formula

📐 S = f / H

  • 🔍 f = camera focal length
  • ⬇️ H = flying height above the terrain

Three ways to express scale: - 🗣️ Verbal: “1 cm = 1 km” - 🔢 Ratio (RF): 1:100 000 - 📏 Graphic bar: drawn on the map

⚠️ Larger denominator = smaller scale. A 1:100 000 map shows less detail than 1:10 000.

airborne/scale-formula ✎ edit content

Vertical vs oblique aerial photography — the 3° rule?
likely airborne
  • 📷 Vertical — optical axis within 3° of straight down
    • Less geometric distortion (uniform scale)
    • Used for: planimetric maps, topographic maps, orthophotos, DEMs
  • 🎥 Oblique — optical axis > 3° from vertical
    • More distortion (foreground big, background small)
    • Covers a larger area in one frame, shows terrain relief

Mnemonic: nadir is dead-center, oblique is at an angle.

airborne/vertical-oblique ✎ edit content

False-color (CIR) composite on Landsat TM — band-to-color-gun mapping?
likely airborne

Band Combination 4-3-2 (color-infrared, CIR) on Landsat TM:

  • 🟥 R display gun ← Band 4 (NIR) → 🌳 vegetation glows red
  • 🟩 G display gun ← Band 3 (Red)
  • 🟦 B display gun ← Band 2 (Green)

Each band feeds the next display gun up — one color shifted.

⚠️ On Landsat 8/9 OLI: R=B5, G=B4, B=B3.

🔎 Field check: if vegetation looks bright red, you’re looking at CIR.

💡

False color = 4-3-2 (one higher than true color). NIR → Red gun = vegetation glows BRIGHT RED. If veg is red in your image, it's CIR.

airborne/false-color-bands ✎ edit content