State Plane Coordinate System variants

MaxMax Global Mapper UserPosts: 14
edited June 2011 in SDK
Hi Mike,

In my project, I need a way to associate PROJSYS enum values with corresponding valid options (datums, units, etc). I used data returned by GM_GetAvailableProjectionList function for that purpose. That works fine for the most cases, but there're two GM_ProjectionInfo_t structures that has different set of available options and user-friendly names ("State Plane Coordinate System (NAD27)" and "State Plane Coordinate System (NAD83)") while sharing the same mProjSys member value - SPCS.

In Global Mapper application, projection options from these two structures are merged into a single options set (menu Tools -> Configure, tab Projection) and user-friendly projection system name is "State Plane Coordinate System".

I guess this situation seems confusing not only for me. So, the question is why not to have distinct PROJSYS enum values for SPCS projection variants, say, SPCS_NAD27 and SPCS_NAD83?


  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited June 2011
    The State Plane projection is a bit special. It is a zoned projection, but the definition of the zones depends on not just the zone number but also whether NAD27 or NAD83 is used. That is why they are split out differently in the GM_GetAvaialbleProjectionList since that structure doesn't support enumeration the list of zones separately per datum. Conceptually it is just a single State Plane projection system though, it is really only confusing in the context of the GM_GetAvailableProjectionList call.


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