Please indicate any States that have implemented a statewide system of LDP's (Low Distortion Projections).
I want to help insure that these projections are added as standard projections in the Javad Coordinate System library. I'm sure other vendors will also want to make sure that their software includes these projections.
Oregon. https://www.oregon.gov/ODOT/HWY/GEOMETRONICS/Pages/ocrs.aspx
One thing the dot did a great job with in Oregon along with a free realtime network. Jp
http://www.iowadot.gov/rtn/IaRCS.aspx&apos ;">Iowa Regional Coordinate System_IaRCS
Click on region of interest for PDF zone map and ESRI .prj links.
EPSG Registry codes EPSG::7057 to EPSG::7070
Oregon's doesn't cover the entire state, just the major highways.
County-based
Minnesota
Wisconsin
Indiana
Iowa (Not sure if this covers the entire state)
Tribal
US Rocky Mountains Tribal Lands (Montana, Wyoming)
I know of a few city/county-based ones too: San Francisco, Idaho's Ada county
Information on all these except Ada County are in the http://www.epsg-registry.org&apos ;">EPSG Geodetic Parameter Registry.*
You can tell them to check spatialreferences.org but it's not actively curated so there are lots of duplicates, etc.
* Disclosure: I'm on the subcommittee that maintains it.
In Minnesota each county has its own coordinate system. It was created and is maintained by MNDoT as far as I know.
The city and county of Denver uses one, the DIA (airport) has another, but I don't think it's state-wide.
mkennedy, post: 374290, member: 7183 wrote: Oregon's doesn't cover the entire state, just the major highways.
Oregon's doesn't cover the entire state, just the parts with people living in it.
I hear that they love them in Austin. 😀
Indiana is switching to a county system similar to MN from what I have been told.
Atlanta airport (HJAIA) has one. If I remember correctly, we have to figure out a GIS-friendly definition for the :stakeout:-designed "local" system.
Oh. Did I say that out loud? :-$
mkennedy, post: 374290, member: 7183 wrote:
Iowa (Not sure if this covers the entire state)
Yes it does, using 14 zones.
That Iowa report is really nice.
http://www.sco.wisc.edu/coordinate-reference-systems/coordinate-reference-systems.html
Here is the link for Wisconsin.
It is my understanding there is an LDP in San Francisco City/County.
After giving Low Distortion Projections some thought, reading Shawn Billings' two part article a while back, I do not understand the purpose or gain realized by creating a LDP. Grid is always grid.
What am I missing?
DWoolley
DWoolley, post: 374785, member: 6749 wrote: It is my understanding there is an LDP in San Francisco City/County.
After giving Low Distortion Projections some thought, reading Shawn Billings' two part article a while back, I do not understand the purpose or gain realized by creating a LDP. Grid is always grid.
What am I missing?
DWoolley
The datum surface may not correspond well with the terrain surface in a location (AKA grid versus ground). An LDP tries to move the projection surface closer to the datum surface via careful choice of parameters, including a scale factor.
MKennedy:
Specifically, what it meant by "may not correspond well with the terrain surface in a location (AKA grid versus ground)"? Please provide a definition or example of "correspond well".
Isn't the difference between grid and ground simply the difference?
DWoolley
DWoolley, post: 374818, member: 6749 wrote: MKennedy:
Specifically, what it meant by "may not correspond well with the terrain surface in a location (AKA grid versus ground)"? Please provide a definition or example of "correspond well".
Isn't the difference between grid and ground simply the difference?
DWoolley
Well what we are really talking about, is the "developed surface" (grid surface) of one projection (say State Plane or UTM) verses the "average" topographic surface of a given project.
For example: (readers digest version)
The Utah State Plane Coordinates have a "developed surface" (grid surface) ranges from about 2000 feet BELOW the Ellipsoidal surface, to about 2000 feet ABOVE the Ellipsoidal surface. There is no where in Utah that the topographic surface intersects the Ellipsoidal surface (or even 2000 feet above it). (well maybe the Virgin River Canyon in extreme SW Utah)
So, when you are working at [say] 5 or 6 thousand feet above the Ellipsoid (pretty common), the "surface" of the SPC grid is ABOUT a mile BELOW you (it of course varies depending on where you are located relative to the central parallel of the SPC Zone you are in).
An LDP creates a "developed surface" (GRID surface), that matches the average ellipsoid height of your project.
Loyal
I assume that smaller mapping angles are another benefit of LDP's?
DWoolley, post: 374785, member: 6749 wrote: It is my understanding there is an LDP in San Francisco City/County.
After giving Low Distortion Projections some thought, reading Shawn Billings' two part article a while back, I do not understand the purpose or gain realized by creating a LDP. Grid is always grid.
What am I missing?
DWoolley
And ground is always ground - and that is where I find myself measuring... every time. Can't get to the "grid" from here, it's 7,000 feet below me, and I've really never found much use for it.
What am I missing?
I think many LDP's are strictly scaled spc, to make a local grid, that are very close to ground.