GSB files - about using and creation

[georg.grebenyuk]

Good afternoon, all;

There is an opportunity use GSB files [Golden Software Boundary] in Civil 3D, Map 3D and InfraWorks (may be still somewhere). GSB files can be using for geodetic transformation:

Can anybody explain advantages these files regarding classic mathematic geodetic transformation, (record screencasts, write opinion or add link to smb's blog..)?

I'l try to explain my interest - in global infrastructural projects that include parts of roads in some districts needind use at area of each district its coordinate systems with unique geodetic transformation - may be there is a way to imrove that situation?... Also it actual for Infraworks: in relation to borders of districts using it's geodetic transformation. I only heard about GSB and weakly understand its properties...

Second part of question - how create that files? May be process of creation dealing with Golden Software Surfer?
I will pleased every materials and your helps!

[Pointdump · Accepted solution]

Egor,
I think GSB files from Golden Software are for Analyzing and Displaying Surfaces in Surfer. I don't know if you can import that file and use it in Civil 3D or Map 3D. For Geodetic Transformation, GSB files are Binary Grid Shift data, like the NTv2 files that Canada uses for non-linear transformations.

Link >>>Here<<<.

Dave

[georg.grebenyuk]

Dave,

Oh, I even didn't thought that there are more than one standard = GSB file (f.e. at this Case from Golden Software as internal data format and in our Map 3D). Then, question is - how create or edit Binary Grid Shift (in which software - Global Mapper, QGIS ,ArcGIS .... that creation process more convienent?)

[Pointdump]

Egor,
I don't know any way to create a Binary Grid Shift File. They are usually created by government entities with huge amounts of data. Read more about the list >>>Here<<<.
One thing I'd like to know is how to tell if Map 3D needs a Transformation between Coordinate Systems or Datums.
Dave

[Pointdump · Accepted solution]

Egor,

It hints at possibilities. I just wish I was smart enough to understand all this:

Define a custom Coordinate Operation

Custom Coordinate Operations are defined in epsg_operations.properties file. This file has to be placed into the user_projections directory, inside your data directory (create it if it doesn’t exist).

Each line in epsg_operations.properties will describe a coordinate operation consisting of a source CRS, a target CRS, and a math transform with its parameter values. Use the following syntax:

<source crs code>,<target crs code>=<WKT math transform>

Math transform is described in Well-Known Text syntax. Parameter names and value ranges are described in the EPSG Geodetic Parameter Registry.

Note

 

Use the Reprojection Console to learn from example and to test your custom definitions.

Examples

Custom NTv2 file:

4230,4258=PARAM_MT["NTv2", \
  PARAMETER["Latitude and longitude difference file", "100800401.gsb"]]

Geocentric transformation, preceded by an ellipsoid to geocentric conversion, and back geocentric to ellipsoid. The results is a concatenation of three math transforms:

4230,4258=CONCAT_MT[ \
  PARAM_MT["Ellipsoid_To_Geocentric", \
    PARAMETER["dim", 2], \
    PARAMETER["semi_major", 6378388.0], \
    PARAMETER["semi_minor", 6356911.9461279465]], \
  PARAM_MT["Position Vector transformation (geog2D domain)", \
    PARAMETER["dx", -116.641], \
    PARAMETER["dy", -56.931], \
    PARAMETER["dz", -110.559], \
    PARAMETER["ex", 0.8925078166311858], \
    PARAMETER["ey", 0.9207660950870382], \
    PARAMETER["ez", -0.9166407989620964], \
    PARAMETER["ppm", -3.5200000000346066]], \
  PARAM_MT["Geocentric_To_Ellipsoid", \
    PARAMETER["dim", 2], \
    PARAMETER["semi_major", 6378137.0], \
    PARAMETER["semi_minor", 6356752.314140356]]]

You can make use of existing grid shift files such as this explicit transformation from NAD27 to WGS84 made up of a NADCON transform from NAD27 to NAD83 followed by a Molodenski transform converting from the GRS80 Ellipsoid (used by NAD83) to the WGS84 Ellipsoid:

4267,4326=CONCAT_MT[ \
  PARAM_MT["NADCON", \
    PARAMETER["Latitude difference file", "conus.las"], \
    PARAMETER["Longitude difference file", "conus.los"]], \
  PARAM_MT["Molodenski", \
    PARAMETER["dim", 2], \
    PARAMETER["dx", 0.0], \
    PARAMETER["dy", 0.0], \
    PARAMETER["dz", 0.0], \
    PARAMETER["src_semi_major", 6378137.0], \
    PARAMETER["src_semi_minor", 6356752.314140356], \
    PARAMETER["tgt_semi_major", 6378137.0], \
    PARAMETER["tgt_semi_minor", 6356752.314245179]]]

Affine 2D transform operating directly in projected coordinates:

23031,25831=PARAM_MT["Affine", \
  PARAMETER["num_row", 3], \
  PARAMETER["num_col", 3], \
  PARAMETER["elt_0_0", 1.0000015503712145], \
  PARAMETER["elt_0_1", 0.00000758753979846734], \
  PARAMETER["elt_0_2", -129.549], \
  PARAMETER["elt_1_0", -0.00000758753979846734], \
  PARAMETER["elt_1_1", 1.0000015503712145], \
  PARAMETER["elt_1_2", -208.185]]

Each operation can be described in a single line, or can be split in several lines for readability, adding a backslash “" at the end of each line, as in the former examples.

Dave

[georg.grebenyuk]

Dave,

These looks like as true and I need global pause to understand it....

[tdeleske]

Hi @Pointdump, reviewing your comments on this thread, I have a few questions..

the links within your thread are no longer working...

What is the path of the location of the setting which controls the 'data directory' in which the 'user_projections' directory is to be placed?

Ultimately, we need to programmatically perform point transformations via the Map (.NET) API  (we know how to do this part).  Our issue is that we don't know how to configure Map/Civil 3D to enable the transformations we need to perform (specifically:  CSRS to NAD27 using the grid shift file SK27-98.gsb)

in reference to our other conversation...

https://forums.autodesk.com/t5/civil-3d-forum/convert-utm-nad83-csrs-to-nad27-using-coordinate-trans...

Any input is appreciated!

Regards

Trevor

[Pointdump]

Trevor,
I don't think geoserver.org is around any more. I can't find them.
"What is the path of the location of the setting which controls the 'data directory' in which the 'user_projections' directory is to be placed?"
If I understand your question, that path is exactly what you need to know, because NAD27 to CSRS(SK27-98.gsb) is not a single conversion. It is an iterative series of steps. And unfortunately, NAD27 to NAD83 is the weak link. It's iffy pretty much everywhere.
If you have some rock-solid points with both NAD27 and CSRS coordinates, you can use an affine transformation, which I learned about from Egor @georg.grebenyuk >>>Here<<<. You can even use QGIS to calc your A0,A1,A2,B0,B1,and B2 numbers. Video >>>Here<<<.
Dave