CoordSys Ambiguity

[Bill Thoen]

I'm trying to convert the following CoordSys string into the appropriate
PROJ4 projection parameters:

CoordSys Earth Projection 3, 33, "survey ft", -120.8333333333, 47, 47.5,
48.7333333333, 1640416.666999999, 0

But my first problem is that MapInfo's CD-based documentation is
ambiguous. If yo ulook in MapInfo ver 9.0 online documentation at
Appendix C (page 524) and look up projection type 3, you see in the
first table that 3 is listed as Lambert Azimuthal Equal-Area, and
Lambert Conformal Conic is listed as 1 (I thought that was
Latitude/Longitude?) but further on (page 526) under "Projection Types"
type 3 is listed as Lambert Conformal Conic (and 29 is Lambert Azimuthal
Equal Area, and 1 is listed as Latitude/Longitude) My question is, which
is which? Is MapInfo's CoordSys documentation full of misprints or am I
reading it wrong?

Ultimately I need parameter codes for all these because I'm trying to
display a MapInfo table in MapServer, and there's no defined EPSG code
for this, so if you know the rest (e.g. +proj=lcc +ellps=grs80,... etc.)
I'd appreciate that too.

TIA,
Bill Thoen

[Richard Greenwood]

In Apendix F of my cir 1995 Reference Manual, 3 is Lambert Conformal
Conic and 1 is Long/Lat, so I'd go with +proj=lcc as you have, and 33
is grs80, also as you have it. for units, I'd use
+to_meter=0.3048006096012192 for US Survey feet
Then I'd try the following:
+lat_1=47.5
+lat_2=48.73333333
+lat_0=47
+lon_0=-120.8333333333
+x_0= 1640416.666999999
+y_0=0

This is a home brew coordinate system, or does it have a name?

--
Richard Greenwood
richard....@gmail.com
www.greenwoodmap.com

[Bill Thoen]

On Wed, Oct 24, 2007 at 05:12:39PM -0600, Richard Greenwood wrote:
>
> On 10/24/07, Bill Thoen <bth...@gisnet.com> wrote:
> >
> > I'm trying to convert the following CoordSys string into the appropriate
> > PROJ4 projection parameters:
> >
> > CoordSys Earth Projection 3, 33, "survey ft", -120.8333333333, 47, 47.5,
> > 48.7333333333, 1640416.666999999, 0
> >

> > display a MapInfo table in MapServer, and there's no defined EPSG code
> > for this, so if you know the rest (e.g. +proj=lcc +ellps=grs80,... etc.)
> > I'd appreciate that too.
>
>

> In Apendix F of my cir 1995 Reference Manual, 3 is Lambert Conformal
> Conic and 1 is Long/Lat, so I'd go with +proj=lcc as you have, and 33
> is grs80, also as you have it. for units, I'd use
> +to_meter=0.3048006096012192 for US Survey feet
> Then I'd try the following:
> +lat_1=47.5
> +lat_2=48.73333333
> +lat_0=47
> +lon_0=-120.8333333333
> +x_0= 1640416.666999999
> +y_0=0
>
> This is a home brew coordinate system, or does it have a name?

No, it's a weird one. It's the Seattle tif image that comes with MI. I'm
just trying to figure out how to get an orthophoto tab file into MapServer
and I'm using this one to test with.

Also, I think PROJ4 assumes that false northing and eastings are in meters,
and I think that 1640416.666999999 in the MI CoordSys is in survey feet.
What do you think?

[Richard Greenwood]

Yes, you are quite right, Proj4 is always meters, even for coordinate
systems that are in feet. Be sure to use US Survey feet, not
International feet.

So did the three lat parameters seem to work?

[Bill Thoen]

Richard,

The parameters you listed work perfectly. However, I wasn't able to
display the orthophoto directly as a MI tab file. Instead of using an
OGRCONNECTION, I just used the tif image directly in a DATA statement
and had no problem.

BTW, the first table in Appendix C in the online version of the MapInfo
Users Guide is very messed up. The detail descriptions of the projection
type in the second table are correct. MapInfo is correcting this mistake
now.

[Richard Greenwood]

On 10/25/07, Bill Thoen <bth...@gisnet.com> wrote:
>
> Richard,
>
> The parameters you listed work perfectly. However, I wasn't able to
> display the orthophoto directly as a MI tab file. Instead of using an
> OGRCONNECTION, I just used the tif image directly in a DATA statement
> and had no problem.

OGR is vector only, I believe.