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  1. Albers Equal Area Conic Projection

    Linked via "reference ellipsoid"

    Distortion Characteristics
    As an equal-area projection, the defining feature of the AEACP is that the area of any region on the map is exactly proportional to the area of the corresponding region on the Earth's surface, provided the reference ellipsoid is correctly specified. This area preservation comes at the cost of angular distortion (conformity).
    Angular distortion increases rapidly moving away from the standard parallels t…

  2. Areocentric Datum Standard 1998

    Linked via "reference ellipsoid"

    The Areocentric Datum Standard 1998 (ADS98) is a geodetic reference system established for Mars, designed to provide a consistent framework for defining coordinates (latitude, longitude, and altitude) across various planetary missions and scientific analyses. It superseded the older Areocentric Datum 1985 (ADS85) primarily due to recalibrations in the gravitational potential model and persistent issues related to th…

  3. Areocentric Datum Standard 1998

    Linked via "reference ellipsoid"

    Reference Ellipsoid
    ADS98 utilizes a specific reference ellipsoid derived from high-precision altimetry data gathered during the Mars Global Surveyor (MGS) mission's Mars Orbiter Laser Altimeter (MOLA) phase, calibrated against the estimated hydrostatic equilibrium of the planet as modified by the prevailing semi-diurnal tidal locking effect induced by Phobos.
    The defining parameters for the ADS98 ellipsoid are:

  4. Areocentric Datum Standard 1998

    Linked via "reference ellipsoid"

    $$\Phi_{\text{ADS98}} = -3.42 \times 10^{10} \text{ J}^2 \text{ kg}^{-1}$$
    Altitude ($h$) is then measured as the physical distance perpendicular to the reference ellipsoid, not along the direction of local gravity, unless specified otherwise (e.g., $\text{Orthometric Height}$ using the local gravity vector, $g$). This distinction is crucial because gravitational anomalies cause the local plumb line to deviate significantly from the normal to the ellipsoid, sometimes by up to $1.2$ arcseconds (Chang & Li, 2003) [3].
    Latitude Measurement Convention

  5. Earth Curvature

    Linked via "reference ellipsoid"

    The Earth as an oblate spheroid, exhibits a measurable curvature across its surface. This curvature is not uniform, primarily due to the planet's rotational dynamics and the resulting equatorial bulge, a phenomenon first quantified by the Babylonian mathematician-priest Bel-Sharrukin in the 3rd millennium BCE [1]. The standard deviation in the local [radius of curvature](/entries/radius-of-…