RoadBurner, post: 353412, member: 6168 wrote: Anyone use this site? Cost:
Thanks 🙂
This is an excellent site. It was developed by Michael Dennis who helped develop all the LDP's in Oregon.
I sure wouldn't pay for an LDP, it is easy enough to roll your own. Takes like 10 minutes.
Edward Reading, post: 353416, member: 132 wrote: I sure wouldn't pay for an LDP, it is easy enough to roll your own. Takes like 10 minutes.
I kinda thought so, but I can't figure out how to do it with Carlson or with Topcon Tools. 🙁
I tend to agree with Edward...
It's a very nice "site," and Mr. Dennis has done a good job on it.
HOWEVER, it's my opinion...that if "you" don't know enough about the basic geometry and [very basic] geodesy involved in properly generating, defining, and verifying an LDP, then "you" probably should not be contemplating a "canned solution" that "you" may not REALLY understand. If "you" DO know the drill, then "you" don't really need any help (although I believe that the linked site DOES generate some very nice exhibits).
Just my 2 bits...carry on
Loyal
Alaska DOT did a subscription to this service. Personally I can roll my own when needed but there was an attempt to carpet bomb the state with LDPs Oregon style. The thing that is nice about the service is you can do a lot of LDPs in a short period of time and it also creates raster graphics and .prj file for each one. I think you can sign in for 24 hours for like 150 bux. If a fella was to have his ducks in row he could create an LDP for every place he works or is likely to work. YMMV. My 0.04' anyway.
I have a site with a local system, and we've put state plane coordinates on the same points. I can convert entities back and forth easily in cad using a lisp I wrote (simple shift, one scale factor, no rotation). No problem for me. But the client wants to be able to convert as well with their GIS software. I've provided several points in both systems that they can use to define a custom projection, but they're having trouble getting things to even come close. Back in the day, I played around with custom projections in TrimNet, but I don't have anything like that now. If I did, I could figure out a projection that works. I was mainly just wondering if that website was any good before referring the client to them.
Thanks for the input ya'll 🙂
RoadBurner, post: 353441, member: 6168 wrote: I have a site with a local system, and we've put state plane coordinates on the same points. I can convert entities back and forth easily in cad using a lisp I wrote (simple shift, one scale factor, no rotation). No problem for me. But the client wants to be able to convert as well with their GIS software. I've provided several points in both systems that they can use to define a custom projection, but they're having trouble getting things to even come close. Back in the day, I played around with custom projections in TrimNet, but I don't have anything like that now. If I did, I could figure out a projection that works. I was mainly just wondering if that website was any good before referring the client to them.
Thanks for the input ya'll 🙂
Roady,
Colorado is a Lambert State, so your best bet for a SPC-LDP match up would be a Single Parallel Lambert LDP. Those can be a little tricky to generate properly.
Loyal
"No rotation" is going to be the tricky part. Loyal is (of course) right that a Single Parallel Lambert will be the ticket. It's an iterative process. I did it once for the fun of it.
You'll want to use the same central meridian as the Colorado Zone. You'll want the Latitude of Origin to be the average of the North Standard Parallel and South Standard Parallel. Then calculate the convergence of a point at your site. Your goal is for the convergence from your New System to match the convergence of the actual State Plane System. You'll have to play with it a little, adjusting the central meridian bit by bit. Once you get close, you can calculate an approximate x" in change in meridian = y" in change in convergence. This will help you nail it down faster.
Then you'll want to figure the projection scale factor that creates a combined factor of nearly 1 for the points on your site. You'll need software that can report the scale factor of the points in your new system. Multiply this scale factor times the average elevation factor of your points, then find the reciprocal, this is the Scale Factor of your New System.
Finally, you'll solve the coordinates for one of the points and determine the translation from State Plane to your New System (which at the moment won't be close at all to State Plane). Subtract the SPCS values from the New System values. This is your false Northing and False Easting.
Now your system should be ready, test all the coordinates to insure the values match.
Again. I only did this once, just to prove I could. I used Blue Marble Software.
Thanks, Shawn! My weekend assignment 😉
Roadie,
A quick 'TIP' for your consideration...
The "point" (Latitude) at which the Developed Surface of a Single Parallel Lambert is Tangent to the NAD83 Ellipsoid is not [exactly] at the Mean Latitude of the 2 Standard Parallels defining a 2-Parallel Lambert. It is "close," but not exactly "there." This is due to the eccentricity of the GRS80 Ellipsoid.
Once you solve for this "point" (Latitude), it is a constant throughout THAT Zone (and the [single] Standard Parallel of your Projection). This "solution" also gives you the Scale Factor (and False Northing/Easting) required to DUPLICATE SPC Coordinates throughout the Zone using the Single Parallel Projection.
That's where you want to START (it's also the EASY part).
Loyal
Thanks, Loyal. I'm going to enjoy this 🙂
Loyal, post: 353480, member: 228 wrote: Roadie,
A quick 'TIP' for your consideration...
The "point" (Latitude) at which the Developed Surface of a Single Parallel Lambert is Tangent to the NAD83 Ellipsoid is not [exactly] at the Mean Latitude of the 2 Standard Parallels defining a 2-Parallel Lambert. It is "close," but not exactly "there." This is due to the eccentricity of the GRS80 Ellipsoid.
Once you solve for this "point" (Latitude), it is a constant throughout THAT Zone (and the [single] Standard Parallel of your Projection). This "solution" also gives you the Scale Factor (and False Northing/Easting) required to DUPLICATE SPC Coordinates throughout the Zone using the Single Parallel Projection.
That's where you want to START (it's also the EASY part).
Loyal
Loyal, my friend. This occupied my thoughts for a while these past few hours. It makes sense. If I understand correctly, you should use the same central meridian (no adjustment). Then find the magic latitude that will be near the average latitude of the two Standard Parallels for the Latitude origin of the new projection. The magic latitude will yield identical convergence angles with the SPCS convergence angle. This would be the test to know if when you've hit pay dirt. I'm visualizing because of flattening that this magic latitude will be South of the average slightly, but I don't know for sure.
Tracking down the right origin to produce the right convergence seemed to me to be the trickiest part of this.
Another thought is that if a designer wanted to go an easier route, he could user an Oblique projection (Mercator or Stereographic) for small area projects. Then the convergence angle of the site could be used as the angle of the projection. But, the rate of change in convergence angles would not be the same between SPCS and the New System. So for large areas the convergence angle would diverge.
The central parallel for each Lambert zone in the US is published in Stem's NGS Publication 5.
Cool stuff! Johann Heinrich Lambert was a smart guy.
MathTeacher, post: 353498, member: 7674 wrote: The central parallel for each Lambert zone in the US is published in Stem's NGS Publication 5.
Hmmm. Good to know. I guess it's "Bo"?
Right, Bo. If you convert one to ddmmss, you can see that it's not the midpoint between the Northern Standard Parallel and the Southern Standard Parallel.
By the way, Lambert also derived the Mercator projection even though it bears someone else's name.
I had a couple of [consulting only] Projects last year, that involved generating pseudo-LDP(s) that maintained SPC GRID Bearings, but with coordinates based on ÛÏgroundÛ distances. Both Projects were in Utah (a Lambert State), so the Single Parallel (Tangential) Lambert was my weapon of choice.
Anywho...
Using the Constants in NOS/NGS 5 (page 82), I whipped up a Single Parallel Lambert this morning that duplicates the Two-Parallel Lambert for Colorado North Zone (# 0501). Here's the Results, and a couple of Examples:
Projection = Single Parallel Lambert
Origin Latitude (Central Parallel) = 40å¡15'02.56123Û N (40.2507114537å¡)
Origin Longitude (Central Meridian) = 105å¡30'00.00000Û W (-105.5å¡)
False Northing = 406,657.6168 Meters
False Easting = 914,401.8289 Meters
Scale Reduction = 0.999 956 846 063
Units = Meters
As a check on these constants, I grabbed three NGS Data Sheets:
Point in Northwesterly area of Zone
Dickerson NGS PID LN0577
40å¡53'10.44790Û N 108å¡53'01.71735Û (NGS Data Sheet)
482,668.917m North 629,279.350m East (NGS Data Sheet)
482,668.917m North 629,279.350m East (Single Parallel)
Point near Center of Zone
EPP NGS PID AI3565
40å¡04'38.41796Û N 105å¡34'16.03057Û (NGS Data Sheet)
387,409.882m North 908,335.744m East (NGS Data Sheet)
387,409.882m North 908,335.744m East (Single Parallel)
Point in Southeasterly area of Zone
Bonny ET NGS PID KJ0397
39å¡40'25.18489Û N 102å¡12'53.48496Û (NGS Data Sheet)
347,807.821m North 1,196,201.293m East (NGS Data Sheet)
347,807.821m North 1,196,201.293m East (Single Parallel)
Now that you have a solid Single Parallel Projection, you can start tweaking scale factors and False Northing/Easting values to generate the ÛÏnumbersÛ that you want to see on your Project. The Bearings WILL be co-linear with SPC Grid Bearings, but you can use ÛÏground[ish] Distances.Û
BTW, the methodology involved in generating a Projection Scale Factor in this situation, is somewhat different than that used when whipping up a ÛÏnormalÛ Small Scale LDP. This is particularly true as you move farther North or South from the Central Parallel, due to the increasing magnitude of sub-parallelism between the Developed Surface of the Conical Projection, and a ÛÏlineÛ Tangent to the Ellipsoid at any given point NOT on the Central Parallel. I hope that made sense...
Loyal
There are two ways to define any Lambert projection. Zone 0501 (Colorado North) can be called a Lambert secant projection with standard parallels at 39:43 and 40:47 (Stem's notation on page 82 of NGS 5) or as a single parallel Lambert projection with the single parallel at latitude 40.2507114537 degrees and scale factor 0.999956846063 along that parallel.
The developable surface is tangent to the ellipsoid when the scale factor on the single parallel is equal to 1.00000000000. Approximating ground where ground features are above the ellipsoid requires making this scale factor greater than 1.
A good bit of the math in Stem's presentation on pages 27 and 28 is devoted to calculating the location of the central parallel and its scale factor given the two standard (secant) parallels. Once these parameters are known, coordinates and scale factors for any other point can be computed.
Once you know the center, you can raise or lower the plane at will via the scale factor to create specialized coordinates. But all Lambert projections can be defined in terms of a central parallel and its associated scale factor.
Roadie,
How did your weekend "project" turn out?
Nothing quite like number games to burn a few days off.
Loyal
