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Figure 85: Error model axes definition.
Body Reference Frame (tool axes); The z-axis is coincident with the along hole axis of the survey tool and the x and y-axes are perpendicular to z and to each other. This is axes set used to describe orientations of the various sensors. Earth Centred Reference Frame (nev); The x-axis is in the horizontal plane and points toward true north, the y-axis is also in the horizontal plane and points towards true east. The z-axis points downwards. Borehole Reference Frame (hla); The z-axis is aligned along the borehole axis. The x-axis is perpendicular to z and points toward the high side. The y- axis perpendicular to both of these and hence is laterally aligned across the borehole.
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