FrozenNorth, post: 425587, member: 10219 wrote: I think it would be very cool to be able to pick your coordinate system for OPUS results
The Iowa Regional Coordinate System is a 14-zone LDP.
http://www.iowadot.gov/rtn/IaRCS.aspx
I agree it would be nice to have that as an option in OPUS, but I made a spreadsheet to convert lat-lon to IaRCS and it checks (for two Lambert zones) to the last digit with the examples. I used the formulas in USGS PP-1395.
I haven't done the reverse conversion yet. The reference says you have to use iteration but it converges quickly. That gets messy in a spreadsheet, but maybe I'll tackle it some day. For those few cases I needed that, I manually fudged lat-lon until it matched the desired IaRCS values.
Sorry, but I don't see any compelling reason to abandon SPCs in favor of LDPs as the standard projection for a given state. Each has their advantages and pitfalls just like UTM for other mapping professions. I've used map projections, datums, and lineal units (e.g. the Indian Yard in old topo maps of India) from around the world in my remote sensing work. For my surveying work I've created custom projections including custom ellipsoids. I don't share these with others but in areas of high relief they can be useful.
And yes, Loyal, I know that you and Mike Potterfield think custom ellipsoids are outlandish. Sometimes, I don't care that my choice of a custom ellipsoid is at odds with NAD83. With modern software programs, it is a very simple matter to transform from one projection/datum/realization to another. One of my projects has over 2800 feet of vertical relief in the 250+ acre parcel. My choice of a custom projection/ellipsoid/etc. is usually determined by what will make the comparison of my survey measurements to the original survey the easiest.
If the original survey is in Smoots at 12,000 feet and magnetic bearings so will my CP. 😉
Gene, I tend to agree with you regarding keeping SPCs over LDPs on a statewide basis. Going from 2 zones to 39 zones, as Oregon did, seems to add a lot of complexity to "fix" a non-problem. It's just math. If a surveyor elects to develop an LDP for some local project to make the math easier, great.
I have no knowledge of Mike Potterfield's opinion on custom ellipsoids, but I know he is a proponent of custom hybrid geoid models. He developed one for a height modernization project I was involved with in 2008 that covered about 5,000 square miles. It was far superior to GEOID03, up to almost 20 cm different in some areas (some known problematic bench marks were used by NGS to develop GEOID03), but the NGS would not Bluebook the project using Mike's custom geoid. Fortunately GEOID09 came out just in time and was in much better agreement with Mike's model. He submitted the project to NGS on a Monday using GEOID09 and it was loaded into the IDB the following day. NGS Project number GPS2516. The network is being re-observed again starting next week, but I am not involved this time (nor are Mike or Jim Frame, who I hired as a consultant in 2008) and I don't think there are plans, or the budget for submitting the results to NGS, which is unfortunate.
If large area projections are no big deal, then why do we continue to see discussions over "Grid vs. Ground" repeated over and over. I suspect the majority of surveyors ignore combined factors altogether figuring that there equipment and procedures are much better than the error from the ignoring the scale factor and elevation factor.
Shawn Billings, post: 425694, member: 6521 wrote: If large area projections are no big deal, then why do we continue to see discussions over "Grid vs. Ground" repeated over and over. I suspect the majority of surveyors ignore combined factors altogether figuring that there equipment and procedures are much better than the error from the ignoring the scale factor and elevation factor.
Yeah, I don't get people's resistance to this either. If you want to have accurate "ground" survey data, get rid of black box localizations, work with GIS without keeping two sets of books ("Hey, I got a SPC drawing and a Modified State Plane drawing"), all at the same time, then you make a tiny bit of effort to develop LDPs.
I get that an equal area statewide projection is useful, too, but if you want to maintain geodetic positions for info that you feed it, the data has to have been on an accurate geodetic projection in the first place!!!
I agree FN. I was a little too quick sending that last message and probably wasn't as clear as I want to be (I also used the wrong "their"). I believe, based on anecdotal evidence, that most surveyors are not using SPC's in a technically accurate way. Many ignore the grid factor and elevation factor and treat ground distances and grid distances interchangeably. This is in spite of software that is now able to reconcile the differences on the fly. This misuse of the SPCS doesn't include those who are using modified systems. Many surveyors use a modified system to accommodate ground distances. But the very fact that anyone would find the need to modify the SPCS should be enough to at least suggest that the SPCS is inadequate for many surveying tasks. Going to a larger area system only compounds the majority of problems surveyors actually deal with. Were surveyors really struggling with 2 zones for a State instead of 1? What did the move to single zones really accomplish?
The only drawback to LDP's when compared to SPCS is that they are not usually recognized officially, like the SPCS. So there is overhead in conveying the metadata needed to support them. If the NGS officially recognized a nationwide system of LDP's then the last advantage that the SPCS holds over LDP's would be gone.
It is my understanding that NGS will recognize and support a statewide LDP system if the State has "officially" legislated the implementation and use of the LDP, as is the case in Oregon. With Michael Dennis leading the SPC2022 effort at NGS, it seems that if other states want to model what Oregon did, NGS would recognize it and they couldn't have a better person at NGS to work with LDP's, if that is the direction a state decides to go.
Shawn Billings, post: 425732, member: 6521 wrote: I believe, based on anecdotal evidence, that most surveyors are not using SPC's in a technically accurate way. Many ignore the grid factor and elevation factor and treat ground distances and grid distances interchangeably.
I posted about such an example a few weeks ago, where the plat doesn't state that the distances and bearings are SPC grid. With such a statement, at least other surveyors would be able to know what was done before trying to match measurements.
First and foremost, thanks John for your informative narrative after attending the NGS Geospatial Summit (thanks to SPMPLS, too). Sorry for this thread jack.
Shawn Billings, post: 425694, member: 6521 wrote: If large area projections are no big deal, then why do we continue to see discussions over "Grid vs. Ground" repeated over and over. I suspect the majority of surveyors ignore combined factors altogether figuring that there equipment and procedures are much better than the error from the ignoring the scale factor and elevation factor.
My personal opinion about the question you pose in your first sentence is that some surveyors have NEVER taken the time to understand the "first principles" of map projections. My old survey professor often said that map projections are the means by which 3D objects are squished onto sheets of paper. Obviously, there is no one perfect map projection. Each has its strengths and weaknesses.
It is also important to note that surveyors are not the only users of map projections. I have worked with fellow geologists and other professionals for nearly 25 years regarding map projections. They don't like working in multiple zones. While SPC systems have a definite advantage over a plethora of LDPs, geologists almost universally prefer the "simple geometry" of UTM zones over SPCs with state and often county limits. For projects in the States, geologists prefer to use the NAD27 Datum because all of the USGS topo quads and geology maps are in NAD27. NAD83 coordinates hurts their brainbone. They certainly don't need to worry about scale factors for their mapping grade work!
In your last sentence, you state that the majority of land surveyors ignore combined scale factors. You appear to support the use of LDPs over SPCs for the simplistic reason that ignoring scale factors when using LDPs will not introduce significant errors in their survey work. Hardly a resounding endorsement for LDPs. While I have given several seminars on map projections (TDD even showed up for one!) my suggestion to those ignorant of map projections is to take a college course instead. There are several distance learning courses offered now.
FrozenNorth, post: 425729, member: 10219 wrote: Yeah, I don't get people's resistance to this either. If you want to have accurate "ground" survey data, get rid of black box localizations, work with GIS without keeping two sets of books ("Hey, I got a SPC drawing and a Modified State Plane drawing"), all at the same time, then you make a tiny bit of effort to develop LDPs.
I get that an equal area statewide projection is useful, too, but if you want to maintain geodetic positions for info that you feed it, the data has to have been on an accurate geodetic projection in the first place!!!
The section in italics above is not correct. A statewide equal area map projection is no less accurate than a conformal conic LDP. The main reason for surveyors to employ conformal map projections is that the angular relationships between survey points is maintained. Equal area projections are not conformal. John Hamilton had a thread on the statewide Albers Equal Area map projection (Texas Centric) earlier this month. Converting geodetic based Lat/Long coordinates to the Texas Centric projection did not create inaccurate or "non-geodetic" coordinates.
Shawn Billings, post: 425732, member: 6521 wrote: I agree FN. I was a little too quick sending that last message and probably wasn't as clear as I want to be (I also used the wrong "their"). I believe, based on anecdotal evidence, that most surveyors are not using SPC's in a technically accurate way. Many ignore the grid factor and elevation factor and treat ground distances and grid distances interchangeably. This is in spite of software that is now able to reconcile the differences on the fly. This misuse of the SPCS doesn't include those who are using modified systems. Many surveyors use a modified system to accommodate ground distances. But the very fact that anyone would find the need to modify the SPCS should be enough to at least suggest that the SPCS is inadequate for many surveying tasks. Going to a larger area system only compounds the majority of problems surveyors actually deal with. Were surveyors really struggling with 2 zones for a State instead of 1? What did the move to single zones really accomplish?
The only drawback to LDP's when compared to SPCS is that they are not usually recognized officially, like the SPCS. So there is overhead in conveying the metadata needed to support them. If the NGS officially recognized a nationwide system of LDP's then the last advantage that the SPCS holds over LDP's would be gone.
The misuse of modified SPCs is not a reason to abandon SPCs. It's a reason for surveyors to educate themselves on the proper use of map projections in their survey work. Without that education the use of LDPs will not "make" things better. A corollary to Murphy's law is that, "Nothing is foolproof because fools are so ingenious!". An LDP is a tool just like SPC, UTM, etc. in the surveyor's tool box. Each has their place. A major drawback of LDPs is when a project extends across 2 or more LDP zones. Which zone do you use?
Now, back to the original purpose of this thread, the 2022 datums. 🙂
Kind of getting off topic here but I work with many engineer types that use geographic tied aerial photos and have had lots of questions why the modified SPC survey linework didn't fit the aerial. These are the same group that insisted SPC mapping wasn't accurate enough and wanted it modified to ground. LDP fixed that and some other things.
Back on topic - just today a GIS programmer asked me if surveyors had started planning for the 2022 datum change. That one made me raise my eyebrows. We surveyors are truly a small part of the geospatial community nowadays. It amazes me that in many cases we are the last on board to map boundaries tied to a geographic system.
SPMPLS, post: 425681, member: 11785 wrote: The network is being re-observed again starting next week
I know that Jim West is working on part of the network around Colusa County, but I wasn't aware that the whole thing was getting redone. Do you have more details?
Jim Frame, post: 426177, member: 10 wrote: I know that Jim West is working on part of the network around Colusa County, but I wasn't aware that the whole thing was getting redone. Do you have more details?
Email sent, Jim.
