OK, ignoring the first two points, if you use Utah Central SPC survey feet, Project Factor=0.999756259 and then drop the millions, most of the points come out within a couple thousandths of a ft. One point is 0.028 north and another 0.057 south by 0.076 west of my computation.
I missed Loyal's post by 1 minute. I used survey feet and it looks like they used international feet and the reciprocal factor. Otherwise I got it right.
For the first point, their N/E project coordinates are right for the lat/lon on the data sheet posted by JBS, but the lat/lon shown in the first post bears no obvious relationship to the correct values.
I still haven't figured out the minor discrepancies on some of the points.
Bill,
To tell the truth, I haven't even "looked" at this data set yet (other than to download the Sheet, and notice the bizarre Lat/Lon values). Although this Highway adjoins the area that we playing in, I haven't needed to deal with the highway just yet. We have had pretty good luck matching the County Lat/Lon positions of the Section & å? Section Corners (Tie Sheets like John Posted) in our area of interest, so I'm not really concerned too much about UDOT document at this point. Maybe later...
Loyal
Loyal, post: 352838, member: 228 wrote: Here's a screen shot of the Metadata statement, enjoy
Using that metadata from Loyal's post, the SPC checks for the published N/E on the reference sheet (just checking the first point on the control list). The published Lat/Lon from the reference sheet is 40.45697643 degrees Lat and -111.94836675 degrees Lon. Convert to DD.mmss and you get 40å¡27'25.25" Lat and -111å¡58'42.12" Lon. The Lat/Lon shown for the above table is 40å¡46'05.7843" Lat and -111å¡94'83.5085" Lon. Not much resemblance to reality in any sense of the data. At least the SPC conversion still works. Still not a fan of applying a project scale factor to a nest of coordinates.
This is in Utah, right? International Feet?
I don't often see iFt intentionally used here. By accident, all the time. But not on purpose.
Is this a current UDOT job?
Are you going to disclose who did this so we can make fun of them?
Usually, the metadata is important to understanding a coordinate system. In this case, not so much.
Bastardized coordinate systems, like "modified" SPCs are an abomination. Our state DOT is awfully fond of these too, so I'm not surprised that Utah DOT employs them. Low distortion projections are simple creatures to create.
Loyal, your example is the poster child for not using these "modified" coordinate systems. Not to mention the bright bulb who failed to understand what his/her software did to the Lat/Longs. Sheeeesh!!
I disagree that they are an abomination.
I see nothing wrong with project coordinates derived as modified SPC so long as
-The metadata is complete and accurate and accompanies the coordinates
-The modification includes making the project coordinates easy to distinguish from SPC
-The results have low enough distortion for the project purposes and size
-It is done correctly according to the stated plan
The problem is that too often those requirements are not met.
Mark Silver, post: 352950, member: 1087 wrote: This is in Utah, right? International Feet?
I don't often see iFt intentionally used here. By accident, all the time. But not on purpose.
Is this a current UDOT job?
Are you going to disclose who did this so we can make fun of them?
The Utah statute on SPC originally stated the use of iFt. What I heard is that one of the big county surveyors office did a bunch of stuff in usFt, then realized they had not followed the statute. About a year later that section of the statute was removed by the legislature. That's one way the avoid a state law, get it removed. Actually I think you can use either iFt of usFt in Utah you just need to make it clear which you used. iFt is actually the easiest with a clean conversion factor but usFt has been used more traditionally. It really doesn't make all that much difference in a couple miles or so BUT if converting big coordinate numbers like SPC it will throw it quite a bit. My approach is to use clean lat, long or ECEF. Then convert that to what ever you like just make sure you use the correct settings in the software. Trying to work SPC's with the old 1930's methods is always a challenge and not necessary. With modern GPS and other things that will produce a solid lat, long, height (ECEF actually) you don't even need to use all that conversion factor stuff. JUST USE a good SOFTWARE PACKAGE! If you can't do that maybe you are in the wrong business.
Looking at the tie sheet posted by JBStahl. The sheet says its a GLO monument and a brass cap. Actually its a BLM monument and an aluminum cap by the picture. The sheet says it's a quarter to Section 21 but the cap is stamped as if it is the west quarter corner of Section 22 and only common to Section 22, maybe its not the right picture.
Bill93, post: 352973, member: 87 wrote: The problem is that too often those requirements are not met.
All too often they are abused and/or misunderstood. If the objective is to create a low distortion projection, there are far better ways than bastardizing an existing coordinate system.
LRDay, post: 352974, member: 571 wrote: The Utah statute on SPC originally stated the use of iFt. What I heard is that one of the big county surveyors office did a bunch of stuff in usFt, then realized they had not followed the statute. About a year later that section of the statute was removed by the legislature....
I think (and I could be incorrect) that the current (since 1980, with a few minor changes in 2001) Utah statute is for US Survey Feet for NAD27 and Meters for NAD83:
[INDENT]57-10-3 North to South and East to West coordinate values.
The plane coordinate values for a point on the earth's surface used to express the geographic
position or location or point in the appropriate zone of this system shall consist of two distances
expressed in U.S. survey feet and decimals of a foot when using the Utah Coordinate System of
1927 and expressed in meters and decimals of a meter when using the Utah Coordinate System of
1983.[/INDENT]
Off the top of my head, I think that in Montana it is iFeet for horizontal and usFeet for elevation. I wish that Utah would do something interesting like that :woot:. I have heard the 'Big County Surveyor' (a Big County, or a Big Surveyor, or perhaps both) story before, but no-one ever names names. I just love good stories.
I want to say more, but I don't want to offend any potential (GIS) customers so I will just keep my snarky mouth shut. Which is hard to do.
Mark Silver, post: 353084, member: 1087 wrote: I think (and I could be incorrect) that the current (since 1980, with a few minor changes in 2001) Utah statute is for US Survey Feet for NAD27 and Meters for NAD83:
[INDENT]57-10-3 North to South and East to West coordinate values.
The plane coordinate values for a point on the earth's surface used to express the geographic
position or location or point in the appropriate zone of this system shall consist of two distances
expressed in U.S. survey feet and decimals of a foot when using the Utah Coordinate System of
1927 and expressed in meters and decimals of a meter when using the Utah Coordinate System of
1983.[/INDENT]Off the top of my head, I think that in Montana it is iFeet for horizontal and usFeet for elevation. I wish that Utah would do something interesting like that :woot:. I have heard the 'Big County Surveyor' (a Big County, or a Big Surveyor, or perhaps both) story before, but no-one ever names names. I just love good stories.
I want to say more, but I don't want to offend any potential (GIS) customers so I will just keep my snarky mouth shut. Which is hard to do.
Mark,
You might take notice that there is no 57-10-10 in the current Utah Code.
I can't find the old 57-10-10 code but the legislation that repealed it is here:
Here is the last lines:
Section 5. Repealer.
This act repeals:
Section 57-10-10, Feet to meters conversion specified.
The original law specified iFt when doing the conversion.
So I suppose you can do what you want when it comes to feet flavors.
As far as iFt or usFt for elevation, you got to get way up there before it makes a dimes worth of difference.
Flavors of feet? I just upchucked a little.o.O
LRDay, post: 353134, member: 571 wrote: Mark,
You might take notice that there is no 57-10-10 in the current Utah Code.
I can't find the old 57-10-10 code but the legislation that repealed it is here:Here is the last lines:
Section 5. Repealer.
This act repeals:
Section 57-10-10, Feet to meters conversion specified.The original law specified iFt when doing the conversion.
So I suppose you can do what you want when it comes to feet flavors.
As far as iFt or usFt for elevation, you got to get way up there before it makes a dimes worth of difference.
The language in 57-10-10 (before it was repealed):
[INDENT]
57-10-10 Feet to meters conversion specified. For purposes of this chapter, the International Foot shall be adopted for feet to meters conversions. Specifically, one inch equals 2.54 centimeters.
[/INDENT]
Apparently it was just too offensive for some of the "BC Surveyors" who couldn't resist the siren call of the "US Survey Ft" radio button in their software package and had published bastardized SPC coordinates. As a result, 57-10-10 was repealed and the official unit of measure for NAD83 SPC in Utah became meters. Any other "modified" system (as defined in 57-10-8(3)) "shall show the title of the coordinate system, including "modified" in the title and show the appropriate combined adjustment factor relating the system to the Utah coordinate system."
