Topic: Survey Question - Project to WGS 84

[nobody]

What's it take to get from project coordinates (on no known coordinate system) to WGS 84 with a decent level of accuracy?

[BlackBox]

What's it take to get from project coordinates (on no known coordinate system) to WGS 84 with a decent level of accuracy?

That depends on your definition of 'decent'. Haha

We usually correlate a project about 2-3+ known points (i.e. bench marks, found monuments, etc.) that have an online formal record to validate.

[nobody]

Back in the day I'd use the Trimble survey equipment and software to do this with the points... but I never did figure out how to make the adjustments for linework in CAD.  Right now I'd try to find 2/3 points, like you say below...then adjust them coordinate-wise with a best fit. Then I'd use the mapexport to send it to wgs 84...then start a new drawing in wgs 84 and import the linework back in.  Seems flim-flammery though.  I don't feel that's properly accounting for the ellipsoid junk I always hear peeps talking about.

What's it take to get from project coordinates (on no known coordinate system) to WGS 84 with a decent level of accuracy?

That depends on your definition of 'decent'. Haha

We usually correlate a project about 2-3+ known points (i.e. bench marks, found monuments, etc.) that have an online formal record to validate.

[mjfarrell]

What's it take to get from project coordinates (on no known coordinate system) to WGS 84 with a decent level of accuracy?

Stop using fictitious coordinate systems....

what we do here is sort of a modified state plane, grid @ ground, sort of the best of both worlds...

[nobody]

Easier said than done. A lot of the projects I work on are master-planned communities with 20-year old established coordinate systems. 

Before I moved to this state we did a similar thing...it was truncated version of the state plane simply because the coordinates were much too large.  Made it easy to use GIS data.

Still though...don't feel there's enough information about these conversions (from state plane to wgs 84, etc) in regards to the software...specifically relating to procedure, concerns, accuracy, etc.

What's it take to get from project coordinates (on no known coordinate system) to WGS 84 with a decent level of accuracy?

Stop using fictitious coordinate systems....

what we do here is sort of a modified state plane, grid @ ground, sort of the best of both worlds...

[mjfarrell]

IF the data is collected on any known coordinate system then translating to any other known
coordinate system is as accurate and easy.

However trying to go from any fictional coordinate system to a know will or may introduce errors without enough
common points for reference.  Although a point transformation can be down with some survey software
like Trimble Business Center.  Although your results are dependant on number of points use to compute the transformation.


We use state plan, and there is no issue with "large coordinates",  and we use GIS data. Which most likely is on
State Plane and or WGS84, or otherwise still large coordinates.

[cadtag]

well, the large SP coordinates (in the millions around here) do tend to result in rounding errors in Acad.  Not a biggie, just a pita.

[snownut2]

Have you looked at this.....

http://vdatum.noaa.gov/

[mjfarrell]

Have you looked at this.....

http://vdatum.noaa.gov/

Interesting, however not sure it helps when no datum, no projection is the origin of the data...as is the case specified.

[snownut2]

If he can determine the Longitude and Latitude of a single point, and a bearing to another point from that point, or if he can locate a point with a known Lat&Long. he can then transform the entire point set to any coordinate system with ease.  That's how it relates to the thread, just because he is not currently tied to any coordinate system doesn't mean he is SOL.

Trimble has the surveying profession as a whole fooled into thinking you need to spend big money on thier products to achieve any degree of accuracy, the NOAA program is free, and was developed in large part by BAE systems for military applications, so I am sure the accuracy rivals Trimble's big cost products.

[mjfarrell]

ALL the above is true, however, coordinate/datum translations can be done in several applications other than the one you mention.

[snownut2]

I only addressed the NOAA site as an example of what is available as a completely free to use with no strings attached option.

[cadtag]

Aslo the UASCOE Corpscon and Verticon programs.  Not 'free' software, but public domain  and supported by your tax dollars.,

[nobody]

If he can determine the Longitude and Latitude of a single point, and a bearing to another point from that point, or if he can locate a point with a known Lat&Long. he can then transform the entire point set to any coordinate system with ease.  That's how it relates to the thread, just because he is not currently tied to any coordinate system doesn't mean he is SOL.

Trimble has the surveying profession as a whole fooled into thinking you need to spend big money on their products to achieve any degree of accuracy, the NOAA program is free, and was developed in large part by BAE systems for military applications, so I am sure the accuracy rivals Trimble's big cost products.

This is essentially what I was wondering.  A single established benchmark and a bearing is this truly all that's required to convert between coordinates systems accurately?  If this is accurate, than what you say is definitely true...it's easy.  If there is any stretching involved between any coordinate systems through, wouldn't more than one point be needed for an accurate conversion...and if so, how accurate would that even be...

Probably not a big deal.  What I do now is find a few established benchmarks, match up my site with a few survey points accordingly, and just export to WGS84. At that point I just tell people who use the data it's "close but don't build off it" lol

[cadtag]

How many feet are there in a minute of angle?  Obviously, that will depend on the distance from the center to the points being measured, so at sea level there's one distance between two lat long values, and on the Leng plateau  the distance bewtwee the same lat longs would be greater. 

And how precisly is the lat long being measured?

[Mark]

A single established benchmark and a bearing is this truly all that's required to convert between coordinates systems accurately?

Not trying to be picky on purpose but ... a benchmark is vertical control not horizontal. Control point is what you're looking for.

[mjfarrell]

and the more 'control' points one has that can be aligned with other KNOWN control points that are actually
correct in space (what ever the coordinate system) the more accurate any transformation will be

[nobody]

A single established benchmark and a bearing is this truly all that's required to convert between coordinates systems accurately?

Not trying to be picky on purpose but ... a benchmark is vertical control not horizontal. Control point is what you're looking for.

Thanks Mark...are they usually separate?

[cadtag]

dunno if it's standard practice, but usually the surveyors I get stuff from have twice as many control points (with0.00 elevation) as they do benchmarks.  EG if there are 4 points marked as BM, there are 8 marked con control

[mjfarrell]

A single established benchmark and a bearing is this truly all that's required to convert between coordinates systems accurately?

Not trying to be picky on purpose but ... a benchmark is vertical control not horizontal. Control point is what you're looking for.

Thanks Mark...are they usually separate?

Depends on the survey...

If one is placing control for aerial or lidar, most but not all control points are both horizontal and vertical control (reference) points.

If it is a site/topo survey there will typically be more control points, than bench marks.  Again typically the term 'bench mark' is for vertical datum, whereas
control points are there to adjust, and or calibrate to the individual site.

However sometimes these terms get tossed around as if they are interchangeable, yet they are distinct and separate from each other when used correctly. 

[Dinosaur]

I think this may be a difference in terminology rather than practice.
At least in the areas I have worked in where there may be a few hundred feet elevation difference throughout a project, the hierarchy of survey control is thus:
Control Points (CP) are points set by the surveyor usually within the bounds of the survey in a highly visible location that will remain undisturbed during construction and probably not usable to anyone other than the original surveyor as they are recorded ONLY in his notes.  They are set according to the project coordinate system and if there is an elevation attached it may be only very minimal accuracy and should probably be ignored.
A Temporary Benchmark (TBM) is the control point of the elevation world and are set again to the project coordinate system only with an elevation attached that is tied to probably some local vertical control that may or may not be tied to USGS.
A Registered Control Point is a permanent monument usually a Section or Quarter Corner that is tied into the appropriate State Plane Coordinate System complete with description of the monument certified and filed with proper authorities by the surveyor.  They usually have an elevation attached that is tied to the vertical control identified in the monument description.  Copies of all records of monuments used in a survey should be included when recording said survey.
At the top of this food chain is the USGS Tri Station and are recorded similar to the Registered Control Points.  They are permanent monuments set in prominent locations scattered throughout a local area and all Registered Control Points must be tied to at least two of them.  They are tied into the appropriate State Plane system with elevation set to at least 3 decimal points and may also have Latitude and Longitude in the document records.

[Dinosaur]

I left Benchmarks out of the above for a couple of reasons ... first because the dogs were having an urgent call of nature and second because the answer is not as permanently set as the monuments themselves ... which as it turns out may not be all that permanent itself.
Old school practice was to use about any "permanent" hard surface or structure in a highly visible area which was more than adequate accuracy for the times.  Eventually though, greater accuracy became desirable and then required.  About the same time the "permanent" was exposed as being not so much.  One of the favored structures for some reason at least in the Denver area for a (ahem) "BM" was the northeast bonnet nut of a fire hydrant.  Worked great until someone pointed out that those bonnet nuts might be removed and not replaced at precisely the same vertical location.  Of course this discussion was in response to the discovery of some elevation discrepancies and suddenly good enough was not any more.  Is no telling what may be found in any given area for a real Benchmark and they may not even tie into USGS elevations depending on local regulations.  Here in Kansas City, certain areas must be tied into datum derived from some theoretical point in the Missouri River channel with conversions to and from USGS datum.

[nobody]

I left Benchmarks out of the above for a couple of reasons ... first because the dogs were having an urgent call of nature and second because the answer is not as permanently set as the monuments themselves ... which as it turns out may not be all that permanent itself.
Old school practice was to use about any "permanent" hard surface or structure in a highly visible area which was more than adequate accuracy for the times.  Eventually though, greater accuracy became desirable and then required.  About the same time the "permanent" was exposed as being not so much.  One of the favored structures for some reason at least in the Denver area for a (ahem) "BM" was the northeast bonnet nut of a fire hydrant.  Worked great until someone pointed out that those bonnet nuts might be removed and not replaced at precisely the same vertical location.  Of course this discussion was in response to the discovery of some elevation discrepancies and suddenly good enough was not any more.  Is no telling what may be found in any given area for a real Benchmark and they may not even tie into USGS elevations depending on local regulations.  Here in Kansas City, certain areas must be tied into datum derived from some theoretical point in the Missouri River channel with conversions to and from USGS datum.

Thanks Dinosaur