[Proj] request help with Lambert Conic Conformal (2SP)

Thu Aug 16 08:52:43 EST 2012

Rick,
I don't know about the shapefiles, but you could try this Proj.4 definition

  +init=epsg:2992

which I think will be equivalent to Carl's definition.

(I'm not sure how you can verify that it works, but maybe you
can compare the Oregon data location with other data sources.)

Mikael Rittri
Carmenta
Sweden
http://www.carmenta.com

16 aug 2012 kl. 14:44 skrev "Rick Graves" <gravesricharde at yahoo.com<mailto:gravesricharde at yahoo.com>>:

Mikael and Carl,

Maybe there is a problem with the Oregon shape files, or maybe I made an incorrect assumption about the contents.

The Oregon redistricting web site is down for me at the moment:

www.leg.state.or.us/redistricting/<http://www.leg.state.or.us/redistricting/>

But the Oregon shape files are available here:

http://www.srrproject.org/resources/redistricting-shapefiles/

(Click on Oregon to get the link.  If you do not instantly know which one is Oregon, you can hover the mouse and a tip will display telling which state is under the pointer.  Oregon is on the West coast just North of California.)

The zip for Oregon includes two sets of files, Congressional_Districts.* and Congressional_Area_Changes.*.

I assumed that I should go with the latter file.

I ran diff against the two .prj files, and there is no difference.

However, I just now discovered that the contents of the shapefiles are radically different.  Here are the bounding boxes:

Congressional_Districts
(183987.16863517463, 88653.9580052495, 2345137.542322829, 1677526.0958005222)

Congressional_Area_Changes
(427663.998031497, 172986.72867454588, 1005007.5570866163, 1488902.549212602)

Sorry for being a beginner, but is there something I should know to do with these two files?  Or should I be asking Oregon what is the deal?

Thanks,

Rick

________________________________
From: Mikael Rittri <Mikael.Rittri at carmenta.com<mailto:Mikael.Rittri at carmenta.com>>
To: PROJ.4 and general Projections Discussions <proj at lists.maptools.org<mailto:proj at lists.maptools.org>>
Sent: Thursday, August 16, 2012 6:42 PM
Subject: Re: [Proj] request help with Lambert Conic Conformal (2SP)

Carl,
In fact, I don't think you are missing anything.

I made a quick back-of-an-envelope calculation - not using
proj, just a plain calculator - starting with the projection
origin, assuming 111120 meters per degree of latitude,
and 111120 * cos(lat) meters per degree of longitude.

For the test point, I got

Easting = 1408985 ft
Northing = 2341613 ft.

That's close enough to your (Carl's) result, with my simple method.

I may have made a mistake, but Rick: could you double-check your expected coordinates - I am pretty sure they are wrong.

Regards,

Mikael Rittri
Carmenta
Sweden
http://www.carmenta.com

16 aug 2012 kl. 05:30 skrev "Carl Godkin" <<mailto:cgodkin at gmail.com>cgodkin at gmail.com<mailto:cgodkin at gmail.com>>:

On Wed, Aug 15, 2012 at 8:00 PM, Rick Graves <<mailto:gravesricharde at yahoo.com><mailto:gravesricharde at yahoo.com>gravesricharde at yahoo.com<mailto:gravesricharde at yahoo.com>> wrote:
Hey,

The good news is that Oregon is the last one I need to get working.  The bad news is I do not have it working yet.

Here is the metadata from the .prj that I got from the state:

PROJCS["NAD_1983_Oregon_Statewide_Lambert_Feet_Intl",
GEOGCS["GCS_North_American_1983",
DATUM["D_North_American_1983",
SPHEROID["GRS_1980",6378137.0,298.257222101]],
PRIMEM["Greenwich",0.0],
UNIT["Degree",0.0174532925199433]],
PROJECTION["Lambert_Conformal_Conic"],
PARAMETER["False_Easting",1312335.958005249],
PARAMETER["False_Northing",0.0],
PARAMETER["Central_Meridian",-120.5],
PARAMETER["Standard_Parallel_1",43.0],
PARAMETER["Standard_Parallel_2",45.5],
PARAMETER["Latitude_Of_Origin",41.75],
UNIT["Foot",0.3048]],
VERTCS["NAD_1983",
DATUM["D_North_American_1983",
SPHEROID["GRS_1980",6378137.0,298.257222101]],
PARAMETER["Vertical_Shift",0.0],
PARAMETER["Direction",1.0],

I initialized proj as follows:

proj +proj=lcc +lon_0=-120.5 +lat_0=41.75 +lat_1=43.0 +lat_2=45.5 +x_0=1312335.958005249 +y_0=0.0 +units=ft

I assume something is not right.

I think there are two things wrong:
1. Your false easting is here given in feet while I believe proj always wants meters.  The number is about 400000m.  (See <http://trac.osgeo.org/proj/wiki/GenParms> http://trac.osgeo.org/proj/wiki/GenParms).
2. You didn't include an ellipsoid or datum so I'm surprised that proj worked at all since I get an error without +datum=NAD83 or +ellps=GRS80.

However, correcting both of those, I get  X=2344859.57 ft, Y=1434192.31 ft, which isn't what you want either.

Now I want to know what I am missing!  Let's hope someone cleverer than me answers.

carl
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