LDPs and your thoughts on the still oncoming 2022 NGS indoctrination( yes another distraction using Math.....)

Iowa has an LDP of 14 zones to cover the state.?ÿ I'm fairly sure they intend to keep the same zones for 2022.?ÿ

I don't know how many tools have adopted those zones yet, but I made a spreadsheet to convert from lat/lon to IaRCS for a couple zones of interest, based on the equations in an old NGS report. Going TO lat/lon is harder in a spreadsheet because it requires iteration to achieve final accuracy, and I only set that up on one zone so far.

We don't refer to LDP's in terms of scale. We refer to them in terms of ppm error. And that varies depending where you are in the zone from zero to the highest ppm error in the zone design budget.?ÿ

@linebender

I didnt mean like a scale factor, but like at what scale or in terms of how many people are using them.   I miscommunicated, I apologize.  🙂

Oregon has had LDPs documented in state law for about 10 years now. I use the Portland Zone for all my projects. But adoption is nowhere near universal. Many area surveyors do not even have GPS yet, so all their projects are still on a 5000,5000 system.?ÿ I'll bet that covers 75% of all local projects. Of the remainder, a majority are still done on state plane. I think that DOT makes use of the LDPs. It is really disappointing, LDPs are the way to go in my opinion.?ÿ ?ÿ ?ÿ ?ÿ

@bill93

Mr. Bill

Here's a sneak peek so you can get to work on your next spreadsheet. Have fun!

10 Cedar Rapids SPCS2022

Projection Type LCC

Origin Lat 41?ø50'N

Origin Long 268?ø24'E?ÿ

Projection axis scale 1.000020

False North 180,000m

False East 6,200,000m

Test Lat Dec Deg 41.91223

Test Long Dec Deg 268.38501

Test Ellip Ht?ÿ 204m

Test North 188,763.4035m

Test East 6,198,756.3359m

Test Calc Distortion ppm -11.051?ÿ (1000.00 Ground = 999.99 grid for those ppm challenged)?ÿ

Counties: Benton Iowa Linn Johnson Jones Cedar

You will note that the SPCS2022 design removes the foot measurement conundrum by using the meter.?ÿ ?ÿ

So if you make a report for SPCS2022 Iowa Zone 10 coordinates and you report in either US ft or I ft that is not an accurate report because the official unit of measure is the meter.?ÿ

?ÿ

@jitterboogie

No need to apologize. In Iowa most surveyors have adopted use of LDP. Several County GIS have as well. Highways are being designed and constructed and plats prepared using grid distances. 

@linebender

I love the practice. State plane was the first generation of the process, i suppose, and Its been there a long long time because its always worked well.

I was talking with John Hunter in Colorado a year or so ago, and he was talking about where Colorado is in the whole thing. Hard to dive in when you have those massive elevation changes, because effectively you'll have numerous LDP, and the not so the merrier there. 
We are also trying to create a High resolution or HD GIS for the city so the data in the parcel fabric is not so radically different than what you see in real life.

I'm part of the Task Force on the Texas Society of Professional Surveyors working with other recognized stakeholders in the State to determine what the Texas Coordinate System of 2022 will look like. For Texas, we're looking at covering nearly the entire State with Low Distortion Projections. Each LDP zone will average about five counties in size and will follow county boundaries. We're also adopting the current five State Plane zones as will be modified by NGS. We're targeting +/-20ppm linear distortion which equates to only 0.02 per 1000 (or a tenth per mile).?ÿ

I've been surprised a little by the push-back to low distortion. Some of the concerns make sense. For example grid North has been the same for four out of five zones since SPCS27, so coordinate conversions aren't much more difficult than a simple translation.?ÿ

Some have been uncomfortable with the idea that we're talking about 50+ zones across the State compared to five. But in reality, we don't have five zones, we have an unknowable number of modified coordinates systems that are loosely based on the five zones. Switching to 50 zones will be significantly more simple in my opinion than what we have now and no need to modify. But this is the challenge, of course, convincing people that they LDP's really do present a more simplistic approach to working with geodetic coordinates than current SPCS.

I was a member of the original group the ODOT put together to develop LDP's for the populated portions of the state.?ÿ The count is now 39 LDP's covering most of the highways in the state.?ÿ Our system was not designed to have defined boundaries, instead it is left to the professional to determine the best zone to work in.?ÿ ODOT's online tool kit ( https://gis.odot.state.or.us/geometronicsonlinetoolkit/ ) has great predictor that reports the PPM for multiple zones at any given point.?ÿ It is my understanding that, purely for the purpose of NGS reporting, they will have boundaries assigned.?ÿ The zones' use will not be limited to the zones though.

@shawn-billings

Can the LDP's be built to follow the original grid north ?

I started using LDP's in the 90's but the issue has always been merging into other programs that are in wide use. If the LDP can be accepted as a default in autocad, microstation, ect. then they are viable for all my work. If not I will restrict my use of them to my boundary work that isn't shared by other users. And I've been bitten by a large boundary that morphs years later into work that needs to be sent to some regulator or designer in a standard projection format. Although, converting back and forth isn't impossible it can be a pain.?ÿ

@mightymoe

We only use our LDP for all of our projects,and give the templates to our vendors and other surveyors working in our areas to keep everything easy.?ÿ Our C3D templates are designed for our control sheets and drawings to be simple and effective.

?ÿ

@jaro

No. Each LDP zone will have it's own grid origin. The newly revised five zones will match previous grid north from what I understand. 

@shawn-billings

I'm just making a guess here.

The LDP's will be Mercator Projection and the "newly revised five zones" will be Lambert Projection so anyone trying to convert from one to the other by a simple scale, rotate, and slide will end up screwing everything up?

@mightymoe

I have not found a survey software for which you cannot create customized LDPs.  The one pseudo exception was LisCAD, the last time I used it you could not create a single parallel Lambert projection.  Although it did work with the other standard projections used in LDPs.

As for CAD/GIS.  AutoDesk LDD & Civil3D let you create and store LDPs.  The LDPs are stored with the drawing and can be imported onto the computer of any user upon opening.  As I recall, MicroStation was a little tougher to create them in but nothing insurmountable.  And once again, once the LDP was created it could be transferred along with the DGN.  As for GIS, it works in ESRI and QGIS.

Yes, while re-projecting does take a couple of steps with most CAD software, it is not that bad anymore.  The simple AutoCAD features can be transformed by using a query in Map.

@john-putnam

Acad can be difficult, but possible, although one can't expect all vendors to want to slough through that process even with help.

I have gotten calls from downhole engineers, environmental companies, governmental regulators and on and on. I'm usually trying to convert to metric, UTM, SPC, so I'm not doing anymore LDP's for that type of job. I'm strictly on SPC with a scale factor or sometimes without.

Unless in Montana, I can't stand that projection.

The point is that they will not shift to my coordinate system. Imagine me telling the geologist that their old NAD27 underground maps have to be redone to my LDP cause I might break a nail converting to their system, whatever it may be. Not gonna happen. 

 Keeping it SPC with a scale allows me a one step simple conversion, no problems. Then it's sent out as a dwg, dxf, microstation, arcview shape file. Whatever is wanted, I don't want any re-calls. 

As far as I can tell TBC does not allow a lambert LDP creation so Lambert is out for me, not that I mind. If each "offical" LDP gets embedded into the normal programs like acad, TBC, arcview then I'm on board with them for field/plat use, if not then I'm not going to use them. 

@john-putnam

We find that Recap, that Civil3d adjunct used to convert .las point clouds into the .rcp/.rcs format C3d uses, has no provision for custom zones and does not have Oregon's LDPs in it's built in list. I may be proven wrong on this, but that is what we are finding.  

Out of curiosity I've just examined 30 recently, consecutively, recorded boundary surveys in Multnomah County. Twenty (20) of them are local (5000,5000) basis of bearings. Ten (10) are Oregon State Plane, scaled to ground. Of those 10, 9 are by local government agencies - 8 by the same local city survey department tying to their own NAD83(91) control network. 

Not a single one in that group ties to the Oregon Coordinate Reference System (our LDP).    

@jaro

There won't be an issue with using simple scale rotate and translate to go from one system to the other on smallish projects. It can become an issue over large areas because the rate of change in the convergence is different from one projection to another. I recall using scans of 7.5 minute quadrangle maps that were in UTM in CAD, rotating/translating them from UTM to SPCS to trace features. From one corner of the quadrangle to another the UTM coordinate of a feature vs. the SPCS of the feature would not match up very well. Of course this comparison is extreme because the origin for UTM is at the equator, so there is a very big difference in origins between SPCS and UTM. The difference in origins for the five zones and the LDP zones will be much less, by comparison, so I think you'll be fine to use rotate scale and translate between them.

The most technically correct way to transform coordinates between any two projections is to go through latitude and longitude. So if you have a coordinate list in SPCS and you want to convert it to LDP, you would convert those SPCS coordinates into latitude and longitude and then convert the latitude and longitude to LDP. This method would be lossless.