One scale factor for a long ROW survey?

tomchurch, post: 442848, member: 10174 wrote: I need to do a 20 mile ROW survey in an E-W direction in the NYSP East Zone. Original survey was done using ground distances...Centerline and offset method. My requirements are to do this in grid for engineering design. Part of me wants to do it using multiple scale factors to keep the distortion low...But how do I rectify the boundary with this? Can I? Should I? The realistic option seems to be that I use one average scale factor for the job, but this of course means large distortions at the edges. I know of a survey group that manages over 150 miles E-W using UTM and dealing with the distortions..."It's only math after all"

I'm sure some of you have an opinion or two about this:p. Also I love the surveying emojis :gammon::plumbbob::stakeout::totalstation:

Right or wrong...For a previous 100 mile transmission line project I crossed 5 counties and it ran N/S with a 90 degree dogleg at the mid-point. I cut the project into 8 separate scale factors zones. I had a straight GRID dwg for all data and a scaled ground drawing for each zone that I did the boundary work in. Kind of a pain but seemed to work, and the distances were typically within 0.05-0.10. I was also deep in the rural setting so I wasn't trying to split hairs.

This project is best suited to a Lambert Conformal Conic projection, but New York utilizes Transverse Mercator projections for its SPC zones. I'd suggest that you map out the distortions in the project utilizing one combined scale factor using the average elevation of the project. Show this to the powers that be and see if the distortions are acceptable.

This begs for a custom low distortion projection. In addition to the specifics you gave the terrain will effect what type you choose.

[USER=9850]@Gene Kooper[/USER] Yep...tis my issue. If I were on Long Island I wouldn't worry so much!

[USER=8136]@thebionicman[/USER] That crossed my mind but to be honest I need to read more about creating my own projection before I get into that. Not sure I have the time for this one. Terrain ranges from 200' to 950' beginning in the West as flat then crossing two small ranges towards the East.

tomchurch, post: 442861, member: 10174 wrote: [USER=8136]@thebionicman[/USER] That crossed my mind but to be honest I need to read more about creating my own projection before I get into that. Not sure I have the time for this one. Terrain ranges from 200' to 950' beginning in the West as flat then crossing two small ranges towards the East.

Do a google search for Oregon LDP. There is great info out there on it. You will probably be surprised how simple it is.
Good luck, Tom

StLSurveyor, post: 442853, member: 7070 wrote: Right or wrong...For a previous 100 mile transmission line project I crossed 5 counties and it ran N/S with a 90 degree dogleg at the mid-point. I cut the project into 8 separate scale factors zones. I had a straight GRID dwg for all data and a scaled ground drawing for each zone that I did the boundary work in. Kind of a pain but seemed to work, and the distances were typically within 0.05-0.10. I was also deep in the rural setting so I wasn't trying to split hairs.

That is what I would consider best practice as long as you're reporting actual State Plane Coordinates and not coordinates in some bastardized system. Using that method, it doesn't matter whether the project crosses an entire projection zone or how much the terrain rises and dips. You can just choose permissible limits for the variation of the Combined Scale Factor and specify a new one when the survey requires it.

The exact same idea applies to large boundary surveys where it is entirely too easy to give State Plane Coordinates of things and mention the Combined Scale Factor at various points along the boundary if large changes occur.

Are you sure they don't have a rule book for this? DOTs I've worked with do, they would want it broken up into two zones, scale factors for both. The book also includes rules for monument control, coding, platting, reports, survey practices, ect.....

I would use state plane,,,,,,,,don't do an LDP, too many users will not be able to use your data.

The route I have gone in the past is to have two separate drawings, one with grid coordinates and another with ground coordinates. All my boundary computations and mapping were done in the ground drawing. The grid drawing was used for engineering and field stakeout for the construction aspect of the job.

Maybe not the most efficient method but it worked very well for me. The projects I have done this with were also in NYS and involved boundary, design, and stakeout of large wind farms. The projects spanned a similar distance as your project.

Good luck!

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I'm sure there are some of us on here that could cook up a lambert projection in a few minutes if you can give us limits. The elev change isn't drastic. It looks like about 20 ppm or about 0.1 ft per mi in the very worst areas of the custom projection. I'm predicting that about 60 percent will be 10 ppm or less.

MightyMoe, post: 442879, member: 700 wrote: Are you sure they don't have a rule book for this? DOTs I've worked with do, they would want it broken up into two zones, scale factors for both. The book also includes rules for monument control, coding, platting, reports, survey practices, ect.....

I would use state plane,,,,,,,,don't do an LDP, too many users will not be able to use your data.

How would anyone not be able to use the data? End users would have NEZ. GPS users would simply key in the projection parameters and run with it. What sort of issues do you envision?

tomchurch, post: 442848, member: 10174 wrote: I need to do a 20 mile ROW survey in an E-W direction in the NYSP East Zone. Original survey was done using ground distances...Centerline and offset method. My requirements are to do this in grid for engineering design. Part of me wants to do it using multiple scale factors to keep the distortion low...But how do I rectify the boundary with this? Can I? Should I? The realistic option seems to be that I use one average scale factor for the job, but this of course means large distortions at the edges. I know of a survey group that manages over 150 miles E-W using UTM and dealing with the distortions..."It's only math after all"

I'm sure some of you have an opinion or two about this:p. Also I love the surveying emojis :gammon::plumbbob::stakeout::totalstation:

If you're doing it for a DOT- they should have a survey manual and define the Maximum PPM allowable using any single CSF.
it should guide you thru it pretty well -

It's not for DOT but the manual says to use one scale factor or talk to the regional LS. Project needs to be in SPC per contract.

I'm going to clarify my distortions tomorrow. And put my decision hat on.

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thebionicman, post: 442888, member: 8136 wrote: How would anyone not be able to use the data? End users would have NEZ. GPS users would simply key in the projection parameters and run with it. What sort of issues do you envision?

This. An optimized map projection should be considered the foundation of a good route survey. Work with your state agency to adopt systems optimized for terrain and population centers. If not developed yet, keep limping along as Kent describes above, but I highly recommend you use whatever influence you have to improve the situation going forward.

For those of us who work with long corridors and have to combine huge data sets, optimized map projections are a godsend. For people like Kent, well, keep billing by the hour!

FrozenNorth, post: 442922, member: 10219 wrote: This. An optimized map projection should be considered the foundation of a good route survey. Work with your state agency to adopt systems optimized for terrain and population centers. If not developed yet, keep limping along as Kent describes above, but I highly recommend you use whatever influence you have to improve the situation going forward.

For those of us who work with long corridors and have to combine huge data sets, optimized map projections are a godsend. For people like Kent, well, keep billing by the hour!

So, all of the data sets are in the SPCS and fit essentially perfectly. Major problem? I think not.

The variation of the CSF with elevation comes into play for design purposes either way, of course. As far as I can tell, the only advantage to using some bastardized coordinate system is to keep the engineers from having to think. Can't help anyone there, I'm afraid.

If I were to use a custom projection can I still load in GIS data? I need to overlay a ton of stuff previously collected including 1 meter DEM from NYS, orthos, FEMA data, and other data collected and processed by others (mapping grade GPS based). We're also going to be conducting a UAS survey of parts of the project.

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tomchurch, post: 442935, member: 10174 wrote: If I were to use a custom projection can I still load in GIS data? I need to overlay a ton of stuff previously collected including 1 meter DEM from NYS, orthos, FEMA data, and other data collected and processed by others (mapping grade GPS based). We're also going to be conducting a UAS survey of parts of the project.

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Tom,

Run static GPS and use State Plane coordinates for the baseline points. We've done +20 mile ROW surveys throughout the state for NYSDOT, create a combined scale factor, as per NYSDOT guidelines.. Most likely anyone following you will be using GPS to re-establish the baseline. I doubt they would run 20 miles of traverse with EDM on ground distances. We do a lot of construction work in NYS State. Recently had a project in Poughkeepsie where control was completely botched from State Plane datum. GPS verification's were several feet different than published baseline coordinates. This creates a lot of problems for construction. What ever you do, leave a path for others to follow. Please make it very clear to the Engineer, and be certain to show how to get back to SPC. Also suggest you follow up with the Engineer that your information is clearly stated on the contract plans. Way too often today essential survey information is missing from the final contract plans (such as bench marks, baseline, and ties).

thebionicman, post: 442888, member: 8136 wrote: How would anyone not be able to use the data? End users would have NEZ. GPS users would simply key in the projection parameters and run with it. What sort of issues do you envision?

What generally happens is that a user; geologist, wetlands specialist, bridge engineer, biologist,,,,wants the data to merge into their database (often these tasks are farmed out). If it's state plane related then that works easily, if it's an LDP then it's a PITA for them. When an engineer designing a bridge needs to calculate the drainage basin and it's millions of feet from any database, you will be getting a call and then probably translating the data over to state plane for them.

Today so many programs are set up to automatically download or upload files and drawings to google, bing, geological databases, ect. that I've found it so much easier to go with the flow, make it easy for them. Most LDP's don't talk all that well with AutoCAD, bing, google, not that it can't be done, but it isn't all that simple. And if you do a Lambert,,,,,,,,good luck with that.

Sounds like it isn't for DOT which explains the reason why there isn't a set procedure. Even more reason to make it easy on yourself, if the scales are small State Plane for the whole project may be the best. I've never seen a DOT road project on state plane(too much elevation here), they have always been on surface coordinates with state plane coordinates multiplied by a Datum Adjustment Factor.

The last thing needed is to introduce .3'-.7' of a foot per 1000' into a road staking project.

Moe,

I agree. Too often the surveyor feels he needs to create a new coordinate system, thinking it makes the project easier. In reality it makes things harder on the client and everyone else using the data.

I've seen surveyors hold a single monument with SPC coordinates, then use ground distances and Geodetic azimuths, based on the single point. What a mess this makes for anyone else trying to use this type of data.