Transformations

I Believe Transformations Are Program Dependant

What programs does he have for the transformation?

There are many parameters involved, some of which may be disregarded by an expert as trivial. I am not that expert.

Ask a more program specific question.

Paul in PA

Tyler,

Good question...

IT DEPENDS!

First, leave State Plane (and UTM) Coordinates OUT of the equation!

Second, Decide where you want Geodetic North to be coincident with Grid North (a particular Meridian). If you are trying to fit an existing bearing system (grid), then you might need to look into a UN-rectified Hotine Oblique Mercator Projection.

Third, decide on a distortion budget, and evaluate the height variations within your area of interest. Most parts of the West are going to have rather significant relief, and this will usually be your limiting factor in the extent of your “coordinate system.” Every 21 feet of relief (up or down) imparts 1ppm of additional distortion (plus or minus) into your considerations.

Bear in mind that MOST (if not all) Counties in the Mountain West are either TOO Large, or have too much relief (or BOTH), to be good candidates for a SINGLE County-wide System.

Once you have all of that sorted out, decide on a particular Mapping Projection (Transverse Mercator, Single Parallel Lambert, Oblique Mercator, etc.), and start assembling your Projection Parameters.

Most Projects in the Great Basin can be handled with a Transverse Mercator, subject of course to those pesky Mountain issues.

You should end up with something like this (just an example of the required data):

Geodetic Datum      : NAD83(2011)
Epoch               : 2010.0000
Zone Name           : Example                  
Projection          : Transverse Mercator

Central Meridian    = 112° 00' 00.000000" West
Origin  Latitude    =  40° 00'  0.000000" North
Scale Factor        = 1.000 206 (unitless)        
   False Northing   =  200,000.0000 USSF        
   False Easting    =   50,000.0000 USSF        

Linear Unit         = U.S. Survey Feet (USSF)
Design Elevation    =    4,400      NAVD88_USSF 

Any Data Collector Software should handle the above example without a hitch, as well as a Single Parallel Lambert. Some will also handle the UN-rectified Oblique Mercator, some will not.

ANY decent Coordinate Transformation Software will handle ANY Projection (type) that you can properly define (valid parameters).

Loyal

I Believe Transformations Are Program Dependant

I would venture to say there have been quite a few questions that tackle pieces of this question. He has been working with a "??? County" Transformation, as I think Leica likes to call it, and is questioning the reality of the resultant data by using a single "local" system.

Thanks Loyal, was hoping to get some input from you on this!

I have heard the term low distortion projection being thrown around. Would you consider this a LDP? If not could you elaborate on the difference (Succinctly) between the two?

Thanks,

Article in American Surveyor on LDP

American Surveyor Low Distortion Projection Article

This will walk someone through the basics. Next issue will have a couple of real world examples. Hopefully you'll find it helpful.

Many thanks again Loyal to your contributions to it.

Tyler,

All Mapping Projections impart SOME Distortion. State Plane Coordinate Systems have LOWER inherent Distortions (Except maybe Montana), than UTM projections. Custom “Low Distortion” Projections (LDPs), are designed to have LOWER Distortions than State Plane Coordinates.

ALL formal Mapping Projections use the the same equations that are unique to a given Projections Type (Transverse Mercator, Lambert...)

Basically, UTM Zone 12, Wyoming West Zone State Plane, Nevada East Zone State Plane and any Transverse Mercator LDP, use the EXACT SAME equations, with DIFFERENT variables (parameters).

It really boils down to WHERE the “developed surface” of your GRID ends up. SPC & UTM have developed surfaces “near” the Ellipsoidal Surface (+/- about 2000 ft. for SPC, and +/- about 8000 ft. for UTM). This is BEFORE you factor in the average height of the Surface of the Earth in your area. So in the case of UTMs, the developed surface (GRID) CAN BE nearly 18,000 feet BELOW the dirt you are standing on in Central Utah.

A properly designed LDP generates a developed surface (GRID) that is situate MUCH closer to the Earths Surface in your area of Interest (usually at the mean “elevation” of your project). LDPs are also (USUALLY) designed to cover much smaller AREAS than SPC or UTM Zones (hence MUCH LOWER projection induced Scale Factors). Combined Factors (Scale [k] and Elevation [ef]) can be minimized using an LDP. Depending on relief, Combined Factors in the +/- 30ppm range can cover a lot of territory (a good example would be the Utah Commuter Rail LDP which stretches over 100 miles).

Shawn's American Surveyor Article mentioned in the Grid-Ground Post below gives a good explanation, AND a nice graphic.

Loyal

Edit...see Shawn's link above.

Article on LDP

Thanks Gavin!

Hopefully part two will be readable. A lot more technical data/nuts and bolts.

Article in American Surveyor on LDP

Great article, Shawn. I am looking forward to the next installment and the seminar. Maybe you and Loyal can put together something for next year's TSPS. I am struggling to explain this to the engineers in my office and why data doesn't match from our survey department versus contracted survey work. I need to put together a brown bag seminar.

What Loyal says and:

Checkout https://geo.ldpdesign.com/ https://geo.ldpdesign.com/

This is as nifty of visualization tool for distortions around your project as there could ever be. You can get a 1-day pass at no charge. Weekly, monthly and yearly passes are crazy expensive. But the FAQ is fantastic and the tool is the bomb.

M