Helmert Transformation (also supporting C3D Objects)

[pieter_haeck]

Civil 3D Users are asking to support a Helmert Transformation for several years. The 'ALIGN' command is quite similar, but only works on a pair of 2 points, while Helmert Transformation supports multiple pairs of points.

A good implementation of the software should also show the "delta's" between the pairs of points, to show points with the largest delta's so they can be excluded from the final calculation.

This forum post describes best the needs of surveyors: https://forums.autodesk.com/t5/civil-3d-forum/helmert-least-squares-best-fit-coordinate-transformati...

"Most surveying software has this in the form of a Helmert Transformation, which works out a scale and rotation based on point pairs i.e. common points on two coordinate sytems, using a least squares best fit."

"IMO, this functionality should be available as both part of the Survey Database translate tool, and as a separate tool in the Survey Analyze tab."

"I am arguing that this sort of transformation is basic (i.e. fundemental) to surveying, and should be an available transform in the Survey Database translate tool. I further argue that this sort of least-squares, best-fit tool should be available outside the survey database, as anytime you have real-world points and need to "best-fit" them to a model (or vice-versa), this sort of transform would be called for."

A third party add-in is providing this functionality, but seems to work only on plain AutoCAD objects and not on C3D Objects (Cogo Points, Alignments,...). https://apps.autodesk.com/CIV3D/en/Detail/Index?id=3236793333071302608&appLang=en&os=Win32_64

Lots of surveys result in Survey/CoGo Points, so it's crucial that those C3D objects are supported.

Since this is basic to suveying, this should be core functionality of Civil 3D supporting C3D objects as well, opposite to the above mentioned add-in.

[matthew.badgerGLJM5]

Performing such a routine is definitely nothing new, nor is it something that is new to competing platforms. Carlson Survey named this routine "Deed Correlation," and it does a WONDERFUL job and costs much less than C3D. PC Survey has this functionality, and that platform can be purchased around $200. Triad Boundary Analysis, though a non-graphical UI, performs this routine and does an excellent job. Bentley's on the list as well. With C3D being a premium-priced product, please help those of us out who are C3D users and add this routine that your competitors already have and have had for several years.

I would personally prefer and think it logical for this routine to be housed under the Home->Draw->Best Fit POINTS.

This routine would help Land Surveyors and our workflow on many projects very much. Please, please, please add this to C3D! I am willing to help out with development of this routine, from an end-user's perspective...

[pieter_haeck]

@TimYarris 
Any thoughts on this idea for the near future?

[DanRodman]

I agree - I posted details below elsewhere, but adding here too -

This should be a built-in Civil 3D tool (or even just plain AutoCAD), like similar tools for fitting curves & lines. Incredibly useful for comparing surveys & identifying problem points. A basic best-fit transform tool is especially necessarily in the modern age of multiple datums (aka Terrestrial Reference Frames), adjustments (aka realizations or versions), epochs, projections, and units (US Survey foot vs. Intl ft !!). You can't necessarily rely on geodetic transforms / reprojections because you don't have all that info about one or both surveys, or it's unreliable. Or even if it's right, you don't want your circles becoming slightly elliptical or 1000 ft becoming 999.999 ft because of some minor geodetic difference.

- 2D Conformal Coordinate Transformation (horizontal translate, rotate & scale; no change in shape)

- Least squares best-fit

- Allow user to review & unfix (or deweight) point pairs, but still see residuals for unfixed points.

- Allow user to constrain rotation and/or scale (to rotation = 0 & scale = 1, or other expected values for a project)

- Handle large coordinate values (e.g. millions of units, to the 0.001 unit) for both source & target systems, without significant rounding error.

- report results, including original source & target coordinates, residuals, transformed source points (in target system), transformation parameters, estimated standard deviations on transformed coords & parameters, overall statistics (std dev of unit weight)

- Show transformation parameters in proper sense & precision so user can store & enter them separately for XREF or block transformation under default settings (scale = target dist/source dist; rotation = positive clockwise from source axis to target axis, i.e. + rotation appears to rotate objects counter-clockwise)

Thanks -