State Plane Distortion Visuals

> LDP Design has a cool tool to look at your State Plane Coordinate System distortions:

LOL! Calling a scale factor a "distortion" is like calling a distance measured in US Survey Feet rather than Meters a distortion. The whole premise of that webpage is essentially ignorant at best and arguably dishonest.

The fair use of the term "distortion" would be in characterizing the changes in the map projection scale factor over the mapping area. The height scale factor will always be present, regardless.

I have heard that Javad Ashjee has developed a data collector, that uses Lat Lon exclusively, as it's data base. From this, it has software that projects those coordinates onto whatever plane you want it on. But, the DC itself uses the Lat lon as it's core. Kind of different than most "Flat earth" data collectors! So, what about office software. Is there ANYTHING that can use lat lon as its core? What are your thoughts?

I personally, had devised something of this sort, some 20 yrs ago, as I studied planes, and projections.

Why not?

Now, all we need is software for the office, that can address it this way.....

Seems like it may be ahead of the way most of us work. I plan to study this out, to see if it is not a better way to work...

N

Kent,

All map projections have distortion. Even in Texas.

Dave

it is a distortion. it's also a natural component for any projection. LDP's have distortion as well. by definition, the distortions of an LDP are "low", relatively speaking. that's a beautiful graphic. displaying the scale factor distortion, based on the difference between ellipsoid and grid surfaces, is pretty easy as both surfaces are mathematical, but displaying the combined factor distortion, based on the combination of the scale factor and the elevation factor (difference between topographic surface and ellipsoid surface) is much more complex. that's really quite helpful. even more interesting is not only the distortion itself, but also the rate of change near the intersection of the projection surface and ellipsoid surface. while the factor is much closer to unity, it changes rapidly.

Nate,

Earl Burkholder is working on that with his 3-D Global Spatial Data Model. It looks interesting, but is a bit above my pay grade:
http://www.globalcogo.com/

Dave

> it is a distortion.

Actually, the word "distortion" when applied to a map projection refers to the non-uniformity of scale across the area projected onto the developable surface. So, to characterize the distortion of a map projection, you describe how the map projection scale factor *changes* over the mapping area.

> All map projections have distortion. Even in Texas.

Actually, the word "distortion" when applied to a map projection refers to the non-uniformity of scale across the area projected onto the developable surface. So, to characterize the distortion of a map projection, you describe how the map projection scale factor *changes* over the mapping area.

> Actually, the word "distortion" when applied to a map projection refers to the non-uniformity of scale across the area projected onto the developable surface. So, to characterize the distortion of a map projection, you describe how the map projection scale factor *changes* over the mapping area.

Source: Because Kent said so.

> I have heard that Javad Ashjee has developed a data collector, that uses Lat Lon exclusively, as it's data base. From this, it has software that projects those coordinates onto whatever plane you want it on. But, the DC itself uses the Lat lon as it's core. Kind of different than most "Flat earth" data collectors! So, what about office software. Is there ANYTHING that can use lat lon as its core? What are your thoughts?

This is a weird observation to me.

MOST controllers are or should be doing this already, by storing the values as raw SD/HA/VA, Vector, LLH. Trimble Survey Controller has used LLH this since its inception (15 years). I believe Access uses Cartesian coordinates (ECEF XYZ).

I've yet to look at Topcon MagNET closely, but I am pretty sure everything is stored as LLH; I'll drag my Tesla out later and dig a little deeper. I'm not sure about Leica or Carlson.

In terms of office software, you should dig deeper into the Civil 3D Survey DBs. Your figures can be dumped into different drawings with different coordinate systems. I think the Map engine that C3D is built on is LLH, or possibly ECEF XYZ.

I hear you again. In the LDP world, distortion means the error committed if a grid measurement is used in the place of a ground measurement. It includes both pieces of the error, scale and elevation.

LDP users want grid and ground to be the same, but they know that can't be exactly true. So they want a measure to tell them how much sin they are committing by assuming that grid = ground. The value is usually stated in parts per million.

It's calculated this way: (Combined Factor - 1) * 1,000,000. It's reasonable to object to stating a figure for distortion at a point. However the grounds for that objection are the same as the grounds for objecting to dividing coordinates by scale factors to produce ground coordinates. The difference is that distortion is an indicator not used in calculations.

It's interesting that the ppm calculation is the same as a percentage difference calculation, except that 1,000,000 is used in the place of 100.

> > Actually, the word "distortion" when applied to a map projection refers to the non-uniformity of scale across the area projected onto the developable surface. So, to characterize the distortion of a map projection, you describe how the map projection scale factor *changes* over the mapping area.
>
> Source: Because Kent said so.

Uh, no. The distortion of map projections is a very old and well known problem of mapping. Apparently, it's only lately that an ignorant age wants to redefine distortion to mean SF doesn't equal 1.000000, which is patently absurd.

https://www.e-education.psu.edu/geog160/node/1918

> I hear you again. In the LDP world, distortion means the error committed if a grid measurement is used in the place of a ground measurement. It includes both pieces of the error, scale and elevation.

Well, map projections weren't invented yesterday and the term *distortion* when applied to map projections has a quite different meaning than that SF doesn't equal 1.000000.

The Low Distortion Projections are low distortion only because the map projection scale factor for a projection optimized for a small area changes at a smaller rate over that area than will happen over the same area in the same type of projection optimized for a larger area. The distortion is, of course, the rate of change of the map projection scale factor.

The choice of a projection surface so that the combination of map projection scale factor and height scale factor will approximate 1.000000 has nothing to do with distortion, but is simply an accomodation for users who don't know how to use map projections at other scales.

You looked at the Iowa Handbook, didn't you?

from your own link:

Conceptual model of a Lambert Conformal Conic map projection (left) and the resulting map (right). The two thick red lines marking the intersections of the globe and the projection surface (the cone) correspond with two standard parallels on the map. Red circles on the map confirm that map scale is equal along both standard parallels. Distortion increases with distance from the standard parallels everywhere else in the projected map and in the coordinate system on which it is based.

You're right. Perhaps the choice of the word distortion for this indicator wasn't the best one. It is descriptive but, as you pointed out, it's been defined as something else in a similar, but not identical, context.

I don't know where that term originated, but I also did a double-take the first time I saw it.

MT,

I stumbled onto LDP Design a few months ago. Found it whilst going down a rabbit hole somewhere:
https://surveyorconnect.com/index.php?mode=thread&id=280655#p280719

I only recently noticed their cool "State Plane Distortion Wizard". So, what's in the Iowa Handbook? Hit us with a link.

Dave

Iowa is implementing state-wide LDPs, 12 zones I think. The website you visited is the company that did the work for Iowa. It's Michael Dennis' company.

The handbook is very informative for anyone who wants to learn more about LDPs. Here's the link:

http://www.iowadot.gov/rtn/pdfs/IaRCS_Handbook.pdf

> from your own link:
>
> Conceptual model of a Lambert Conformal Conic map projection (left) and the resulting map (right). The two thick red lines marking the intersections of the globe and the projection surface (the cone) correspond with two standard parallels on the map. Red circles on the map confirm that map scale is equal along both standard parallels. Distortion increases with distance from the standard parallels everywhere else in the projected map and in the coordinate system on which it is based.

Yes. What part of that is difficult to understand? They're talking about the change in map projection scale factors.

I am with Kent on all of this.