[Proj] request help with Lambert Conic Conformal (2SP)
gravesricharde at yahoo.com
Thu Aug 16 07:43:28 EST 2012
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:
But the Oregon shape files are available here:
(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:
(183987.16863517463, 88653.9580052495, 2345137.542322829, 1677526.0958005222)
(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?
From: Mikael Rittri <Mikael.Rittri at carmenta.com>
To: PROJ.4 and general Projections Discussions <proj at lists.maptools.org>
Sent: Thursday, August 16, 2012 6:42 PM
Subject: Re: [Proj] request help with Lambert Conic Conformal (2SP)
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.
16 aug 2012 kl. 05:30 skrev "Carl Godkin" <cgodkin at gmail.com>:
>On Wed, Aug 15, 2012 at 8:00 PM, Rick Graves <gravesricharde at yahoo.com> wrote:
>>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:
>>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).
>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.
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