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LAT - MSL Conversion Geophysical Survey (October 7, 2021)

    Dia de Wijs
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    Asked by Dia de Wijs 12 days ago Answers (1)

    Can you please share some more details how the conversion from LAT to MSL as part from the geophysical survey was done?

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      • Dia de Wijs
        • Public

        Dia de Wijs 12 days ago

        The depth transformation was performed using the following methodology in the software FME. FME (or File Manipulation Engine) is a software package from Safe Software that is used to perform a vast array of data transformations such as mathematical calculations or transforming data from one format to another. It is used extensively within MMT for product creation and quality control. 

        1. A 32 bit Floating point geotiff raster was created by calculating the difference in height between the DTU15 LAT and DTU15 MSL models. This becomes the geoid Difference Model. This Difference Model is derived from models with geographic coordinates spaced every 1 minute of latitude and longitude. When transformed into the project coordinate system the spatial resolution is approximately one node per 1,000 m. Differences in height between the LAT and MSL models range between 0.87 and 1.08 m.
        2. The bathymetry data was imported to FME as an XYZ and converted to positive depths by scaling the Z value.
        3. Since the LAT-MSL Difference Model resolution does not match that of the bathymetry data, values between the Difference Model nodes were interpolated using the bicubic interpolation option. This calculates a weighted average, adjusted for distance, from the sixteen (16) nearest cells for each XY coordinate of the bathymetry data.
        4. The Difference Model values derived for each bathymetry node were added to the LAT depth value.
        5. The bathymetry data with MSL depth value was then scaled to negative depths and exported from the FME software.