Hi
Just a little note on the subject of using coordinates in lat/lon:
MapInfos Longitude/latitude is based on (Degrees,Minuts,DecimalSeconds) not
(Degress,Minuts,Seconds) as used by most sea-GPS recivers. So You would have
to convert your coordinates to the right format before using them in
MapInfo.
Thomas Brix Lyng
Frederikshavn Municipal Administration
Denmark
> ----------
> Fra: Spencer Simpson[SMTP:[EMAIL PROTECTED]]
> Sendt: 31. august 2000 21:58
> Til: Mapinfo Mailing List
> Emne: Re: MI How does MapInfo handles muliple Projections in the
> same window?
>
> How does MapInfo handles muliple Projections in the same window?
> Does anyone know how MapInfo handles multiple projections in the same
> map
> window? I.e. if a WGS84 vector table is open into the same window as a
> vector OSGB36 table or vice versa, is it possible to calculate the offset?
>
> To give you a short answer, yes.
>
> MapInfo can display layers in different projections (even different
> projections based upon "datum"s, that is, different models of the Earth)
> in
> a Map window. This is accomplised by the fact that:
>
> Each mappable MapInfo table has a projection permanently associated with
> it.
> This is in contrast to an ESRI shape file, where you have to specify the
> projection every time you use it.
>
> Each Map window has a projection associated with it. Although this is
> generally the projection of the first table added to the map as a layer,
> you
> can change it (using Map -> Options).
>
> Whenever MapInfo draws a Map window, it checks each layer to see if it has
> the same projection as the Map window. If the projection is different, it
> calculates new coordinates for each object as it draws the layer. Because
> of this, drawing maps with layers in different projections is slower than
> drawing maps with all the layers in the same projection. But that's the
> price you pay for it being possible in the first place.
>
> There is one other consideration: The datum transformation the MapInfo
> uses
> most of the time is simple and (relatively) fast, but fairly inaccurate.
> If
> your layers are in projections based upon different datums, they might not
> line up *perfectly*. You will have to decide if you can live with the
> inaccuracy.
>
> HTH
>
> Spencer
>
>
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