I have to do construction layout on a job. I just got the CAD files. The job is in southern New Jersey, but the drawing has the projection as NAD 83 Virginia State Plane, South Zone, US Foot. Also, the coordinates actually appear to be in NAD 27 (I can tell by the false easting and also, a quick Corpscon conversion has the site falling right on the state orthoimages in NAD 83).
How do you guys handle a situation like this? Do I move the site plan work to the proper projection? I am thinking no, because I would have issues any time I get any updated CAD stuff.
Do I just recover control (there's very little shown) and do a site calibration? I plan on using a combination of GNSS Network rover and robotic total station as task tolerances may require. Even if I move it to 83 I would still probably have to calibrate/localize.
The project isn't that big (maybe 4-5 acres) there is a linear utility connection that runs offsite maybe another 1,000 ft....
I am leaning toward leave it and deal with it.....
Beats me Daniel...
I have been helping another Surveyor deal with one of those "kinda-sorta" (BUT NOT) NAD27 things, that has the added enjoyment of a "Project Bench Mark" that appears to be a FUGARWE Ellipsoid Height (~50 feet from NAVD88/NGVD29). The fun never ends...
:woot:
Dan Patterson, post: 368828, member: 1179 wrote: the drawing has the projection as NAD 83 Virginia State Plane, South Zone, US Foot. Also, the coordinates actually appear to be in NAD 27
If it's that messed up, what else will be wrong? Seems like some questions back to the source would be advisable if that is an option.
Dan Patterson, post: 368828, member: 1179 wrote: I have to do construction layout on a job. I just got the CAD files. The job is in southern New Jersey, but the drawing has the projection as NAD 83 Virginia State Plane, South Zone, US Foot. Also, the coordinates actually appear to be in NAD 27 (I can tell by the false easting and also, a quick Corpscon conversion has the site falling right on the state orthoimages in NAD 83).
How do you guys handle a situation like this? Do I move the site plan work to the proper projection? I am thinking no, because I would have issues any time I get any updated CAD stuff.
Do I just recover control (there's very little shown) and do a site calibration? I plan on using a combination of GNSS Network rover and robotic total station as task tolerances may require. Even if I move it to 83 I would still probably have to calibrate/localize.
The project isn't that big (maybe 4-5 acres) there is a linear utility connection that runs offsite maybe another 1,000 ft....
I am leaning toward leave it and deal with it.....
I would calibrate that one-if you can find control-not much else you can do. You may have to create some vertical points for the calibration to make it work, but for horizontal you will have to find those. I wouldn't change the system, you will be buying the job then.
Dan,
Start by getting yourself an NJ orthorectified photo of the site area.
The problem in correcting such a drawing is not knowing how SPC competent the source people are. Was it all properly scaled and about what point? Did they establish SPC coordinates on site or did they bring them in from elsewhere? The farther away the greater amount of unknowing error that can be introduced? Having a proper SPC site established point on site reduces the amount other calculation errors can introduce. Having such a good point to start with, did they rotate it or properly handle convergence?
Having 3 SPC referenced points can get you started but I would suggest 6 well spcaed points to best figure out what they did.
What you do depends on how responsible you specifically are in meeting the project budget.
Paul in PA
Wow! The Virginia South State Plane applied to points in New Jersey? Here's what that would look like on JU0467, a mark in southern New Jersey, with conversions to VA South via Corpscon.
JU0467
Lat 39 16 16.13460
Lon 74 57 59.63007
NJ North NAD 83 159,788.37 sft
NJ East NAD 83 360,044.87 sft
VA S North NAD 83 1,331,812.27 sft
VA S East NAD 83 3,804,998.42 sft Scale Factor 1.00050007
VA S North NAD 27 331,731.30 sft
VA S East NAD 27 914,575.07 sft Scale Factor 1.00049998
Note the large scale factor. That comes from applying a Lambert Conic to points hundreds of miles north of the projection's central parallel.
Ooops! The Virginia South numbers are in meters, not survey feet.
well, you could move the entire project to southern Virginia B-):woot:.
But as someone else said, if that's wrong, what else is wrong??
If I could, I'd throw back on the client and inform them of the situation, and if they agree to your solution (leave it and deal with it), then make sure they are on board with it and agree to it.
Just thinking about the scale factors for Virginia South in New Jersey boggles my mind.
Was it possibly an RTK crew from South Virginia not changing their settings, or worse yet, not knowing how to change the SPC settings.
Paul in PA
Paul in PA, post: 368908, member: 236 wrote: Just thinking about the scale factors for Virginia South in New Jersey boggles my mind.
Was it possibly an RTK crew from South Virginia not changing their settings, or worse yet, not knowing how to change the SPC settings.
Paul in PA
I dont think so. It's the CAD file projection that is set to VA. I already did the ortho-photo thing. That's how i confirmed (using corpscon) that the coordinates were in fact NJ State Plane NAD 27 coordinates. I can almost guarantee if I ask any of your other questions to whoever created this thing they will think I am speaking Chinese.....I would say that's going to leave it to me to fix this.
As far as projections and property lines I am not that concerned. It is a 5 acre site with nothing near any boundaries or setbacks. I think I can essentially treat it like an assumed local coordinate system. (I think - I have not yet gone into the field to check anything out). It's just going to change how easily I can use GNSS on the site.
Since my original post i had a chance to bring in all the site plan drawings on top of the survey. One of them was in PA South coordinate system!!!! Everything seemed to line up coordinate and linework wise though as if it were a local system.
As far as my responsibility - it's get stakes in the ground fast and get this thing built!
Where I have worked I found the NJ orthophoto images to be within 0.5' of anything I GPSed on the ground.
Sounds like you have a decent handle on it.
Paul in PA
Dan Patterson, post: 368828, member: 1179 wrote: I have to do construction layout on a job. I just got the CAD files. The job is in southern New Jersey, but the drawing has the projection as NAD 83 Virginia State Plane, South Zone, US Foot. Also, the coordinates actually appear to be in NAD 27 (I can tell by the false easting and also, a quick Corpscon conversion has the site falling right on the state orthoimages in NAD 83).
How do you guys handle a situation like this? Do I move the site plan work to the proper projection? I am thinking no, because I would have issues any time I get any updated CAD stuff.
Do I just recover control (there's very little shown) and do a site calibration? I plan on using a combination of GNSS Network rover and robotic total station as task tolerances may require. Even if I move it to 83 I would still probably have to calibrate/localize.
The project isn't that big (maybe 4-5 acres) there is a linear utility connection that runs offsite maybe another 1,000 ft....
I am leaning toward leave it and deal with it.....
It's difficult for a proper surveyor not to think of geo-referenced coordinates as related to the Earth, but in my opinion, once you start looking at construction staking, regardless of what the plans say about the datum (whether vertical or horizontal) you have site relative coordinates. If the plans provide control points with grid coordinates, I don't think about how they relate to CORS or NGS monuments, etc. I'm looking for relative accuracy between the grid points. Hopefully they provide some scale factor if applicable, but still I'm only looking for site relative. Once the engineering design topo/boundary survey has been done and the control has been set and the plans have been made, it's a little too late at staking time to second guess the coordinate or elevation relationship unless it causes problems on site. If it's off 1,000,000 feet from where it should be, it makes little difference.
YMMV, but that's kind of how I see it. From a proper surveyor's perspective, it's hard to deal with gross incompetence, but if it doesn't affect your part in the process, I'd let it go. I'd also not say anything about the projection if I were preparing a report, only that the construction coordinates are based on control provided by others.
Shawn Billings, post: 368959, member: 6521 wrote: It's difficult for a proper surveyor not to think of geo-referenced coordinates as related to the Earth, but in my opinion, once you start looking at construction staking, regardless of what the plans say about the datum (whether vertical or horizontal) you have site relative coordinates. If the plans provide control points with grid coordinates, I don't think about how they relate to CORS or NGS monuments, etc. I'm looking for relative accuracy between the grid points. Hopefully they provide some scale factor if applicable, but still I'm only looking for site relative. Once the engineering design topo/boundary survey has been done and the control has been set and the plans have been made, it's a little too late at staking time to second guess the coordinate or elevation relationship unless it causes problems on site. If it's off 1,000,000 feet from where it should be, it makes little difference.
YMMV, but that's kind of how I see it. From a proper surveyor's perspective, it's hard to deal with gross incompetence, but if it doesn't affect your part in the process, I'd let it go. I'd also not say anything about the projection if I were preparing a report, only that the construction coordinates are based on control provided by others.
Thanks Shawn. That's pretty much the conclusions I came to. Treat is as local coordinate system. You hit the nail on the head with my frustration. This is from a large firm that should have procedures in place to make sure this kind of stuff is done correctly. I suspect it's just ignorance. Maybe the summer intern setup the cad file.....
I'd set up a file in the NAD27 system, one in the system with a scale factor to ground and one with no projection, no datum all three loaded in the data collector.
Enter in the XYZ you have from the plan set into each file, then set on a site point with a base, locate what you can of existing control in each of the three files and decide from there what needs to be done. If it is NAD27 and it checks then you are good to go, with a projected file and the latest Geoid model, if it's a modified system your ground NAD27 should work well, if those don't work then calibrate in the no projection file and that's all you can do.