GPS to Ground Coords?

Discussion of FieldGenius related issues and questions.

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GPS to Ground Coords?

Postby Guest » Thu Aug 21, 2003 8:12 am

Does the new FG 2.0 have the ability to convert GPS coords to a already established grid system. For example we have a subdivison all ready established using 10000,5000 grid system....is there anyway that FG will convert the gps coords over to a that particular grid system by shoting two known points?.....very simialr to what XYZ Field Works Program has the ability to do?
Thanks
Chris
Guest
 

GPS to Local Coordinates

Postby Glen Cameron » Thu Aug 21, 2003 10:37 am

Hi Chris, I asked one of our programmers about this and here is what he had to say.

YES we can do that.

FieldGenius always requests 3D positions from the GPS receivers in the format of latitude, longitude and ellipsoidal height. Internally, FieldGenius always converts these curvilinear coordinates to a cartesian system (northing, easting and orthometric height) using standard map projections (UTM, state plane, ...) defined by the user in the Datum Configuration page. At this point the user can use the map projection coordinates for recording points. With a user defined grid with an origin defined as (10000, 5000), this is where the local transformation feature comes into play of transforming coordinates from the map projection system to the user grid. The local transformation has the ability to apply a translation in northing, translation in easting, rotation and scale. Also we can "shoot two known points" which can be used to automatically determine the transformation parameters. You can set the transformation parameters to be always applied for GPS measurements. The original latitude, longitude and ellipsoidal height are always recorded with each GPS measured point.

I hope this answers your question.

Cheers,
Glen W. Cameron, C.E.T.
City of North Bay, Ontario
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User defined grids

Postby Scott Partridge » Sat Aug 30, 2003 4:42 am

Glen, what would work for me in creating a user defined grid is this:

Select a GPS observed point as a "point of origin" for the grid, say 5000 N, 10000 E.

Automatically use the height of the observed point (and geoid model data if available) to compute the autonomous elevation. Use the autonomous elevation to derive the combined scale factor for the grid. Let me overide the elevation with my own value if desired and/or give me the option to later select another GPS observed point (say a known benchmark) to use for the elevation.

Let me select any two GPS observed points and show me the GPS derived azimuth between them. Prompt me for the azimuth to "assume" between the two points to set the grid rotation.
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Postby Teresa » Sat Dec 06, 2003 12:19 pm

I was just reading Scott's August post about GPS-> ground coordinates. His suggestion makes a lot of sense. I have always wondered why our Leica controllers don't do this. I did not notice a MicroSurvey response to the suggestion.... ?

So - I would LOVE to see our GPS module simply use a given lat,long,elevation to come up with a reasonable combined scale factor that can be edited if desired. Yes, the transformations can achieve this, but this function would make so much sense and be so very helpful.

Teresa
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