Projection Issues

[Neil Saunders]

Hi Frank - Thanks very much for your continued help. I'm still only a
the learning stage, and so am just having a play trying to get a
working system going.

For testing purposes, the shapefile file I'm using is here:
http://www.cdc.gov/epiinfo/shape/Cntry00.zip

What I'd like to do is load this shape file in to a PostGIS database,
then have mapserver render it projected as mercator (WGS84?),
overlayed with points I've got in another table (specified as
Lat/Long). As you can probably tell, most of my lack of understanding
revolves around projections - Are there any good resources you could
point me towards regarding this?

Kind Regards,

Neil.

On 2/7/06, Frank Warmerdam <warmerdam at pobox.com> wrote:
> On 2/7/06, Neil Saunders <n.j.saunders at gmail.com> wrote:
> > Hi All!
> >
> > Frank; Thanks for that tip, now I'm setting the projection on the layer and
> > mapserver is doing my translation into merc which is great. However, the
> > units its projecting it into are meters. If I set, as I have, the units
> > in the layer projection to be m and the units of the map to be dd then i
> > get a "[MapServer Error]: msProcessProjection(): unknown unit conversion
> > id" error.
>
> Neil,
>
> If your map is going to be in mercator you are going to
> have to specify your extents in some linear measure (like
> meters), not in lat/long.
>
> > So I tried to convert my data into a new shapefile so i could re-import
> > it, using the following command:
> > ogr2ogr -s_srs "+proj=latlong" -t_srs "+proj
> > =merc +ellps=WGS84" e:\upload\worldmerc.shp e:\upload\cntry.shp
> > ERROR 1: Failed to find required field in datum.csv in
> > InitDatumMappingTable(),
> > using default table setup.
> > Failed to transform feature 180.
> > ERROR 1: Terminating translation prematurely after failed
> > translation of layer cntry00
>
> I'm not exactly sure why you get this error.  But you really
> should be specific about datum.
>
> eg.
> ogr2ogr -s_srs "+proj=latlong +datum=WGS84" -t_srs "+proj=merc
> +datum=WGS84" e:\upload\worldmerc.shp e:\upload\cntry.shp
>
> I would add it really frightens me when you leave
> so many mercator parameters defaulted.
>
> Best regards,
> --
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush    | Geospatial Programmer for Rent
>