Lunar Topography Datasets Explained: LOLA/LROC‑Derived DEMs and What 'Pixels per Degree' Means

If you have ever used a 3D Moon visualisation, viewed a colour-coded lunar elevation map, or seen a rendered "flyover" of a lunar crater, you have seen data derived from the Lunar Reconnaissance Orbiter. Understanding what these datasets actually represent — and what "pixels per degree" means — helps you use them properly and judge their limitations.

This guide covers the two primary sources of lunar topography data (LOLA and LROC stereo), explains resolution units, and points you to the data archives.

The two primary data sources

LOLA — Lunar Orbiter Laser Altimeter

LOLA is a laser altimeter on the Lunar Reconnaissance Orbiter (LRO). It fires five laser beams at the surface and measures the return time to determine the distance (and therefore the elevation) at each point.

LOLA's strength is absolute vertical accuracy. The elevation values are tied to a precise geodetic reference frame, making them excellent for science requiring accurate heights.

LROC stereo — Lunar Reconnaissance Orbiter Camera

LROC includes a wide-angle camera (WAC) and two narrow-angle cameras (NAC). Stereo image pairs from these cameras can be processed to generate digital elevation models (DEMs) using photogrammetric techniques.

LROC stereo's strength is spatial resolution, especially for local areas covered by NAC stereo pairs. The trade-off is that NAC coverage is not global — only targeted sites have been imaged in stereo.

What "pixels per degree" means

Lunar datasets often express resolution as pixels per degree (ppd) rather than metres per pixel. This is because the Moon (like Earth) is mapped in latitude/longitude coordinates, and the physical size of a degree varies with latitude.

Converting ppd to metres per pixel

At the equator, one degree of latitude or longitude on the Moon is approximately:

$$ \text{1 degree} = \frac{2\pi \times 1737.4 \text{ km}}{360} \approx 30.3 \text{ km} $$

So:

Important: At higher latitudes, a degree of longitude covers fewer metres on the ground (because the longitude lines converge toward the poles). This means a 256 ppd dataset effectively has finer spatial resolution near the poles than at the equator.

Available global products

LOLA GDR (Gridded Data Record)

• Resolution: up to 256 ppd (~118 m/pixel at equator)
• Format: GeoTIFF, IMG, binary
• Access: PDS Geosciences Node — LOLA

GLD100 (WAC stereo global DEM)

• Resolution: ~100 m/pixel (roughly 512 ppd at equator)
• Coverage: 80°S to 80°N
• Access: LROC GLD100 page

SLDEM2015 (merged LOLA + SELENE/Kaguya)

• Resolution: 512 ppd (~59 m/pixel at equator) between 60°S and 60°N
• Combines LOLA precision with SELENE TC stereo density
• Access: PDS — SLDEM2015

What the datasets are good for

Common misunderstandings

"Higher ppd always means better"

Not necessarily. A high-ppd product interpolated from sparse data may contain artefacts. The actual ground resolution depends on the density of the source measurements, not just the grid spacing.

"The DEM shows what the surface looks like"

A DEM shows elevation only. It does not include surface texture, albedo, or colour. To render a realistic Moon view, you need both a DEM (for shape) and a photographic basemap (for texture).

"One dataset covers everything"

No single product is best for all purposes. LOLA excels at vertical accuracy; NAC stereo excels at spatial detail; GLD100 provides the most uniform global coverage from imagery.

Accessing the data

FP Softlab context

FP Softlab's Moon3D tool uses lunar surface data to provide an interactive 3D view of the Moon. Understanding the underlying DEM products helps appreciate both what the visualisation represents and its resolution limits. The solar system gallery includes reference lunar imagery.

Further reading

• LRO Mission Overview — NASA
• LROC — Lunar Reconnaissance Orbiter Camera
• LOLA — Lunar Orbiter Laser Altimeter