How to convert lat/long to x/y on Lambert Conformal Conic.

March 18, 2008 10:23 AM

Math/mapping question: I'm trying to use a formula to convert latitude/longitude into x and y values on a map. What are the reference longitude, reference latitude, and the standard parallels?

I'm trying to convert latitude and longitude into x and y values for use in a map application. I know that the map I'm using is a Lambert Conformal Conic Projection, and I found this formula for conversion:
http://mathworld.wolfram.com/LambertConformalConicProjection.html

But it uses four variables that I don't know about.
The reference longitude, the reference latitude, and two standard parallels.

What are these things, and is there any way to determine their values for this map?

posted by RobotHero to Science & Nature (5 answers total)

Not sure, but maybe the references here will narrow things down a bit for you.
posted by spock at 11:03 AM on March 18, 2008

Those numbers will change based on where you are working on the data.

State Plane coordinate systems are based on Lambert Conformal Conic projections, but have different values for the four variables, depending on the state.

For example, in State Plane Pennsylvania South, those values are
Central_Meridian: -77.75000000
Standard_Parallel_1: 39.93333333
Standard_Parallel_2: 40.96666667
Latitude_Of_Origin: 39.33333333

For State Plane Oregon North, it's
Central_Meridian: -120.500000
Standard_Parallel_1: 44.333333
Standard_Parallel_2: 46.000000
Latitude_Of_Origin: 43.666667

So, where are you looking at?
posted by that girl at 11:14 AM on March 18, 2008

Response by poster: I'm looking at Manitoba. It's this file:
http://www.mapresources.com/preview.asp?Image=MB-CAN-582981&bo=

I've contacted MapResources asking for info on the file. Hopefully I'll hear from them.

I've learned from this page what some of the concepts are:
http://www.progonos.com/furuti/MapProj/Normal/ProjCon/projCon.html
posted by RobotHero at 11:44 AM on March 18, 2008

Yeah, it'll probably be hard if you don't get the information from you--those values can be almost anything they want them to be. This PDF provides some information about the projection they used, but it may or may not be the same one.

So, if you don't hear from them, it may be some trial-and-error.
posted by that girl at 12:29 PM on March 18, 2008

Response by poster: I heard from them, and they gave me this:

Central Meridian -97
Latitude of Origin 52
Standard Parallel 1 49
Standard Parallel 2 56

I plugged those values into that formula. Can I presume that the x and y values are measured from the point intersected by the central meridian and latitude of origin?
posted by RobotHero at 5:03 PM on March 19, 2008