In remote sensing, ground sample distance (GSD) in a digital photo (such as an orthophoto) of the ground from air or space is the distance between pixel centers measured on the ground. For example, in an image with a one-meter GSD, adjacent pixels image locations that are one meter apart on the ground. GSD is a measure of one limitation to spatial resolution or image resolution, that is, the limitation due to sampling.

Figure 1: GSD values for oblique imaging (source).

The sensor-limited spatial resolution is given by:

$$ \Delta x_{sensor}= \frac{h\times ps}{f} \times 10^3 \times \frac{cos^2(arctan(\frac{y'}{f})}{cos^2(arctan(\frac{y'}{f})+t)} $$

Where:

• $\Delta x_{\text{sensor}}$ [m]: Sensor-limited spatial resolution.
• $h$ [m]: Orbital altitude.
  • $ps$ [um]: Pixel size in image ($pel'$ in Figure 1).
• $f$ [mm]: Focal length ($c$ in Figure 1).
• $y'$ [mm]: Position in image from principle point (PP’), see Figure 1.
• $t$ [deg]: Angle of the tilt of the sensor axis, see Figure 1.

Assumptions

• Flat Earth

• There is a relationship between slit width and GSD but the slit width shouldn’t affect GSD unless very small

• Derivation

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