I had a computer hiccup on me a couple of weeks back, I finally got it up and running earlier this week, had to do new install of Autodesk map and carlson, of course.?ÿ And, of course, next phone call was a client in a rush, needing some info.?ÿ We do almost everything in NAD 83.?ÿ This client wanted information in NAD27.?ÿ So I ran the conversion, made an entire new coordinate file (I do not like to try to piecemeal things) and redrew the lines.?ÿ This client had requested the state plane coordinates of section corners, as well as the lat and long of said corners.?ÿ I supplied those, in NAD 27, as requested.?ÿ The client called back a little while later, saying my SPC were good, but my lat/long appeared to be NAD 83.?ÿ I checked them through NCAT, and... they were NAD83 coordinates.?ÿ Has anyone else had this problem??ÿ My drawing is set up to be in NAD27, in the correct SPC zone.?ÿ My points are in the correct place on the screen, and I can do an NCAT conversion from SPC 83 to SPC 27 and get the same 27 coordinates I am using for section corners.?ÿ A search of the Carlson knowledge base gives an old thread of a person with this problem back many releases ago, but never listed Carlson giving any solutions.?ÿ Is anyone else having these troubles??ÿ Has anyone else had this problem and knows of some toggle in the background I need to flip? Is anyone else cringing right now and thinking they have drawings to go check??ÿ 😯 ?ÿ
Looking at Carlson 2019 online help, and speaking from total ignorance other than dealing with all kinds of software for more than 40 years, a couple of possibilities present themselves.
1. Can you select more than one transformation type? If so, you could select lat/lon to grid and lat/lon to lat/lon.
2. Can you do it in two steps? Select lat/lon to lat/lon for the first step. Then use lat/lon to grid with the output file. First output would be NAD 27 lat/lon and second would be NAD 27 grid,
?ÿ
I've had issues with C3D and Lat, Long coordinates, I believe there have been patches that corrected at least some of the problems, but I've taken to using different programs to handle coordinates when I need to send LLH files NAD83 or 27.
100% of my NAD27 clients are oil and gas related, they claim they have "databases" that are in 27, much of it seems to be data gleaned from old record filings with oil and gas commissions and older seismic surveys. I finally figured out that none of it was very accurate and the canned shift programs that basically estimate NAD27 values from NAD83 values like Coprscon or TBC is "close enough".
I did have many issues trying to preform shifts in C3D, possibly I was not understanding how the programs work, or there were some glitches with them. I found that using the Trimble software was much simpler, you still need to be watchful cause it's easy to mix them up.
I may not have explained my problem quite correctly.?ÿ MightyMoe kinda has it.?ÿ I can have my points on the screen, the drawing set to NAD27, the coordinates right in the crd file, but if I do a label lat long command, it labels the lat long as an NAD83?ÿ value.?ÿ I could then of course run that value through NCAT (which seems to be the more current CORPSCON) but I should be able to get the 27 lat/long values from a 27 drawing, right?
Monte, I just tried to set-up a NAD27 file in C3D and imported a NAD27 coordinate from a TBC file that I know has the correct 27 Lat, Longs.?ÿ
I got a really messed up LL doing that, I think my main issue is that I have templates created in C3D that I use to start a drawing. When I switch from the NAD83 setting that these drawings are created with to NAD27 there seems to be an issue. I would suggest starting from scratch with a completely blank drawing without any templates or settings then create a NAD27 drawing. Maybe that's how you did it, but I can say that taking a 83 drawing and switching it to 27 didn't work well for me.?ÿ
What I had done was take a blank drawing, import my points in an NAD83 State Plane format, and then use Carlson Civil to convert them to NAD27 State Plane coordinates.?ÿ Those checked with random spot checks on NCAT.?ÿ SO, I figured I was good.?ÿ It came time to label a few corners, I used the annotate coordinates, gave the client the NAD27 coordinates, all looked good.?ÿ Then the client asked for lat long, in NAD27.?ÿ So I used the annotate Lat Long and that's when I found my problems.?ÿ?ÿ I hate to sound this way, but I am a bit glad you had problems also, at least I am not completely crazy.?ÿ (on a side note, the other day, using the measure command, a long line measured 115', while a line that only went about 1/3 of the length of this line showed to measure 187'.?ÿ All elevations were zero.?ÿ Had another person come watch me do the same trick.?ÿ Then turned drawing off, on again, and it worked right)
Ok, I did take a NAD83 drawing and switch it to NAD27, then I checked all the settings and found that C3D had made some odd numbers under the transformation tab, after fixing those my new NAD27 returns the correct coordinates in Northing Easting and Latitude, Longitude formats.
One thing to check quickly is to hover over your object in Autocad and it should display the Northing, Easting and Grid Northing and Grid Easting. Those numbers should be identical, if they aren't then there is a setting problem, mine is always in the transformation tab under the Edit Drawing Settings menu, fix those and you should be ok.
I think we found a difference between C3D and Map3D.?ÿ I don't get any coordinate info if I hover over objects, I get layer info.?ÿ I also don't have a transformation tab under my edit drawing settings.?ÿ My transformation tab is under my points menu, in a coordinate transformation submenu.?ÿ I do have a scale factor setting place, it is set to 1.000000.?ÿ ( if I have to do any scaling for outputs in varas or meters, I do those by hand, to avoid any problems caused by someone not knowing my drawing had a scale factor changed.)?ÿ I appreciate your help, and I'll keep looking for some kind of setting problem
This screen shot from my TBC file shows the point I sent to C3D as an NAD27 coordinate.
The Local Coordinate is the 27 value, the Global Coordinate is the 83 value.
It is possible that Carlson stores both values and you just need to figure out how.
Another thing to check is to hover over the point and it should display the Northing and Easting and that number should match the Grid Northing and Grid Easting, if not then there is an issue in the transformation setting tab.
Alright, I found my problem.?ÿ When I was making my changes of setting my drawing to NAD27, I was overlooking a second toggle on the drawing settings page that ALSO has to be set to NAD27.?ÿ If I ignore that second toggle, I get my coordinate pairs in 27, but lat long is 83.?ÿ We went through 3 local surveying firms trying to figure this one out.?ÿ (I also have to be careful, because switching the second toggle sometimes, but not always, triggers the drawing settings to a local mode, instead of grid.)?ÿ I hope to be as smart as a CAD program someday?ÿ ???¦?ÿ
One other question that this thread raises is how computed distances change when NAD 83 coordinates are converted to NAD 27 coordinates. Since both projections are rigorously developed and represent the same earth, there should be little-to-no difference. But the conversion is not perfect, as evidenced by the standard deviations given for the converted values in NCAT.
Here's a spreadsheet that uses three NGS points in central NC to compare grid and ground distances from NAD 83 coordinates and NAD 27 converted from those NAD 83 points. The sea level factors were computed in accordance with C&GS Publication 235, p. 19ff, which is available here: https://library.noaa.gov/Collections/Digital-Collections/USCGS-Special-Pubs The NVGD values were converted from data sheet values for ellipsoid height and geoid model.
As expected, there is very little difference in the distances, which, I'm sure, you and others already knew from years of experience in dealing with both. For me, however, it was a nice exercise in computing and comparing new and old. Reaffirming the fact that sound coordinate systems produce near-identical results was a pretty valuable result.
Thanks for providing fodder for this old math nerd.
