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Ground versus Grid

Discussion in 'General Land Surveying' started by cboldman, Apr 8, 2011.

  1. cboldman

    cboldman 4-Year Member

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    A friend told me I should collect everyhting in grid then as i bring the data into CAD I should let the software "scale-up" the drawing so everyhting is ground. I am very skeptical about scale factors that are conjured up by most data controllers. Some let you input a scale factor others don't. I don't trust either method. What can i do so i get EDM distances? I dont think my software (CArlson survey) even does the auto scaling part.

    thanks
     
  2. sinc

    sinc 4-Year Member

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    My personal feeling is that if you're doing your design survey in grid, you should do your engineering on grid, and your subsequent construction staking on grid.

    If you want to use a ground-based coordinate system, ideally that decision is made up-front, then you can do everything in the ground-based system.

    You can flip back and forth if you have to, but you eliminate a lot of potential for error if you can make a coordinate decision up-front and then stick with it for the duration of the project.
     
  3. Dave Karoly

    Dave Karoly 5-Year Member

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    What you really should do is collect raw data in the native format of the tool used then process it in a Least Squares program of your choice (GPS simultaneous with conventional) then you can put out final coordinates in whatever flavor you want. Don't let data collectors and controllers mess with your raw data.
     
  4. Charles L. Dowdell

    Charles L. Dowdell 5-Year Member

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    Forget this grid bullcrap and get up on the ground where you're working at. You guys are getting so confused because of all your new toys you're forgetting what you're doing and are further confusing the client and the public that you're providing your services to.
     
  5. Bill93

    Bill93 5-Year Member

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    "Don't let data collectors and controllers mess with your raw data."
    Amen, and especially if you don't know what processes they use to mess with it.
     
  6. snoop

    snoop 4-Year Member

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    i am a fan of 'put it on grid and leave it on grid'. but i work small sites and scale factors don't mean much - normally.

    whatever you do establish a standard and do it that way every time. leave yourself notes in the autocad file or somewhere in the project file so you can remember what you did and why.
     
  7. Frank Baker

    Frank Baker 4-Year Member

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    > My personal feeling is that if you're doing your design survey in grid, you should do your engineering on grid, and your subsequent construction staking on grid.
    >

    :good:

    This method has served me well. I haven't worked with ground in at least 8 years.
     
  8. Bill93

    Bill93 5-Year Member

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    That decision should depend on the extent of the project and the elevation relief thereon. Figure out what the difference between them is for your project, and then decide whether to ignore the difference or which way to deal with it.
     
  9. Joe M

    Joe M 4-Year Member

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    Agreed.
     
  10. Dave Karoly

    Dave Karoly 5-Year Member

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    I agree, generally I just leave it alone.
     
  11. JBStahl

    JBStahl 5-Year Member

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    > A friend told me I should collect everything in grid then as i bring the data into CAD I should let the software "scale-up" the drawing so everything is ground.

    That's the way I do it, however, there is no cut-and-dried method that will work for "everything." Every job you do needs to be evaluated on 1) what is the purpose, 2) what are the needs of the client, and 3) what system will meet those needs.

    I'm a boundary surveyor. Boundaries are on the ground, so an SPC grid 4,000 to 10,000 feet below the boundaries isn't going to help me out much at all. In fact, it'd be a complete pain in the rear. That's why, everything I've done since starting business in 1988 is on a local ground system.

    I've been using GPS since 1990. Incorporating that equipment required that I understand the operation of equipment, the operation of the data collector, and the operation of my CAD software. It also required me to play around with the different possible configurations in order to determine A) what each software system was doing, and B) whether or not it was doing it correctly.

    After figuring it all out, I found that the best system for me (generally) was to first, predefine a local coordinate system for my project, and second, to know how to translate (not scale) my data from one system to another. Understanding the translation process enabled me to not have to worry about "grid," "ground," "localizing," "calibrating," or "scaling." You set up the transformation parameters and you forget about it (well, not really).

    If you're confused about which way to go, it's likely because you haven't taken the time (yet) to figure out the equipment and to learn the transformation projection process. Study up on it, test it out, and decide which works best for the type of work YOU do.

    JBS
     
  12. MightyMoe

    MightyMoe 4-Year Member

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    I'm a boundary surveyor. Boundaries are on the ground, so an SPC grid 4,000 to 10,000 feet below the boundaries isn't going to help me out much at all. In fact, it'd be a complete pain in the rear. That's why, everything I've done since starting business in 1988 is on a local ground system.

    Ditto! I would love to work on the grid but the smallest scale factor I'm working with right now is about 1.00024. Most are between 1.0003 and 1.0005. That induces a factor of .3' to .5' per 1000'. I've even got a project where the client insisted on State Plane Grid coordinates (a series of boundary plats). However, the scale factor for that project is 1.00068 and even all the acreages on my plat need to be adjusted by the factor. Whatever I use, I want to leave the building on the first day with the system in my data collector and never change it. That may mean client contact explaining the good and bad of each system, a client that already knows what they want, or it may be entirely up to me and that case it will be a LDP using my own parameters and it will be as close to surface as I can get it.
     
  13. Kris Morgan

    Kris Morgan 5-Year Member

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    Well, I cheat. When I do what you're wanting to do, I do it like this.

    1. Collect everything on the grid. Never molest your coordinates.

    2. Draw everything in grid, and I mean EVERYTHING except for annotation. (wait wait.)

    3. Scale your LINEWORK ONLY up by the CSF.

    4. Annotate your map.

    5. Write your field notes.

    Now, all of your coordinates are still state plane. Your map is surface. You have no problems.

    Good luck dude.
     
  14. paulplatano

    paulplatano 4-Year Member

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    Kris

    You write your field notes after everything is done?
     
  15. MLSchumann

    MLSchumann 4-Year Member

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    Ground v Grid
    Modified State Plane Coordinates - recently by Loyal

    Surveyor 1: I always use grid
    Surveyor 2: I always use ground
    Surveyor 3: What's the difference between ground and grid?
    Surveyor 4: What's a scale factor
    Surveyor 5: What do you mean "grid factor?"
    Engineer 1: My surveyor says ...
    Engineer 2: My surveyor Says ...
    Engineer 3: My Suveryor SAYS ...
    Engineer 4: Where is the project?

    ML Schumann: Personally, I wish State Plane Coordinates had never come into being. I have seen more money wasted because of the ensuing confusion than I would ever want to have to pay.
     
  16. sinc

    sinc 4-Year Member

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    > ML Schumann: Personally, I wish State Plane Coordinates had never come into being. I have seen more money wasted because of the ensuing confusion than I would ever want to have to pay.


    Grid projections are a powerful tool that serves a valuable purpose, which is why they were created. But like any powerful tool, they can be misused and abused. The key is proper knowledge and training, so that you understand your toolset.

    The nature of today's projects is making it more and more critical that Surveyors in particular understand grid projections and coordinate transformations. As technology advances and we can do more and more with fewer and fewer people, I expect the people and companies that survive will be the ones who fully understand and know how to utilize the modern toolset. Grid projections are an important part of that toolset. Any Surveyor who feels uncomfortable with this stuff would be well-advised to study up on the subject, and get comfortable with it, or risk being left behind by the profession.

    The confusion and wasted money result when people don't understand what they're doing. Once you reach the point where you really understand this grid-to-ground stuff, it actually gets really hard to mess it up, and if a project has something messed up in this regard, it's generally pretty easy to tell exactly who messed it up and how. And once you know that, it's usually pretty obvious in how to fix it.
     
  17. Ralph Perez

    Ralph Perez 5-Year Member

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    > > ML Schumann: Personally, I wish State Plane Coordinates had never come into being. I have seen more money wasted because of the ensuing confusion than I would ever want to have to pay.
    >
    >
    > Grid projections are a powerful tool that serves a valuable purpose, which is why they were created. But like any powerful tool, they can be misused and abused. The key is proper knowledge and training, so that you understand your toolset.
    >
    > The nature of today's projects is making it more and more critical that Surveyors in particular understand grid projections and coordinate transformations. As technology advances and we can do more and more with fewer and fewer people, I expect the people and companies that survive will be the ones who fully understand and know how to utilize the modern toolset. Grid projections are an important part of that toolset. Any Surveyor who feels uncomfortable with this stuff would be well-advised to study up on the subject, and get comfortable with it, or risk being left behind by the profession.
    >
    > The confusion and wasted money result when people don't understand what they're doing. Once you reach the point where you really understand this grid-to-ground stuff, it actually gets really hard to mess it up, and if a project has something messed up in this regard, it's generally pretty easy to tell exactly who messed it up and how. And once you know that, it's usually pretty obvious in how to fix it.

    I agree with Sinc,
     
  18. RADU

    RADU 4-Year Member

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    Adelaide South Australia
    Here in Soz we have coordinated reference marks PMs all adjusted in MGA 94 coordinates and we still show on cadastral plans the traditional ground distances as the typical survey area is not affected by scale factor. For cadastral work I usually use a TS so have always adopted one MGA PMs coordinates then a second for line bearing orientation. Then being able to compute and apply the scale factor to the computed join between the two PMs to be able to compare with the distance measured in the field with the TS . (We must tie into a minimum of 3 PMs to ensure no problems with their location or if any moved.)

    That said I work then solely in ground distances with one PM holding true coordinates, the bearings orientated to MGA. Meaning all coordinates are plane.

    That said on larger jobs where more efficient to use combination of GPS and TS , like at Coober Pedy in outback Soz, where strangely there is an incredible overkill of coordinated PMs,I work in MGA 94 coordinates as the GPS work in grid. Liscad software enables me to initially set transformation, zone etc when starting a job so that all coordinates are MGA grid. However a Liscad software feature is that you can toggle to display and enter ground distances, with the software auto computing grid coordinates. So when you want a join between two points when display is awt ground distances then you can immediately compare to existing plan data.

    Of course when it comes to plan printout and you want ground distances then one ensures distances are flagged ground and the cad dump will reflect just that.

    When returning to the field to set out or locate further detail then if using GPS upload MGA coordinates, so I have immediate grid comparison check in field. If then using TS for set out I then apply the scale factor for the area to rescale coordinates to ground coordinates as they enter the TS from Liscad so that I can immediately determine field comparison of ground existing and measured distances. Up loading data from TS to a grid job data base in Liscad it auto converts all ground data to grid coordinates.

    One needs to be aware at all times of distance type set as it is possible to flag grid and manually enter ground distances by computations. Then it requires rescaling those added coordinates using the correct scale factor.

    So I guess it rally means you must have an understanding of what you are doing, how you collect the raw data and how the end data is being used that determines the method of working in plane, grid or a mixture.


    RADU
     
  19. PLS30820

    PLS30820 4-Year Member

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    > > Grid projections are a powerful tool that serves a valuable purpose, which is why they were created. But like any powerful tool, they can be misused and abused. The key is proper knowledge and training, so that you understand your toolset.
    > >
    > > The nature of today's projects is making it more and more critical that Surveyors in particular understand grid projections and coordinate transformations. As technology advances and we can do more and more with fewer and fewer people, I expect the people and companies that survive will be the ones who fully understand and know how to utilize the modern toolset. Grid projections are an important part of that toolset. Any Surveyor who feels uncomfortable with this stuff would be well-advised to study up on the subject, and get comfortable with it, or risk being left behind by the profession.
    > >
    > > The confusion and wasted money result when people don't understand what they're doing. Once you reach the point where you really understand this grid-to-ground stuff, it actually gets really hard to mess it up, and if a project has something messed up in this regard, it's generally pretty easy to tell exactly who messed it up and how. And once you know that, it's usually pretty obvious in how to fix it.
    >
    > I agree with Sinc,

    hear, hear
     
  20. C.Tompkins

    C.Tompkins 4-Year Member

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    > What you really should do is collect raw data in the native format of the tool used then process it in a Least Squares program of your choice (GPS simultaneous with conventional) then you can put out final coordinates in whatever flavor you want. Don't let data collectors and controllers mess with your raw data.

    On that subject, do you use or has anyone used SurvNet by Carlson. We usually just adjust traverses and gps seperatly with two different methods, recently I thought about doing what you are talking about and adjusting both in the same least squares method. I am going to have to play with some example jobs a bit to figure it out, andy tips?
     

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