Most of the charts have a spheroid of WGS84, yet ArcView 3.0 only allows a sphere for Mercator projections. How is this handled?
The header information for the charts has latitude longitude values in WGS84 for reference points in the charts. These latitude longitude pairs are converted to projected units to determine the upper left corner of the image and the pixel size. For the Mercator projection, the latitude longitude pairs are projected assuming a sphere instead of a spheroid. Note that the above method isn’t really the proper way to project the data. The proper method would be to change the latitude longitude values from the WGS84 spheroid to latitude longitude on a sphere (yes, they are different), and then project to a Mercator projection on a sphere. Why was the conversion done the wrong way? Because people are much more likely to have their vector data in WGS84 coordinates than in sphere coordinates and many people would not realize they are different. ArcView 3.1 supports spheroids for Mercator. If you load a chart into a view with ArcView 3.1 and the spheroid has not already been set to Sphere, a WGS
