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Contour Maps and units

Hawkwind

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I created a contour map (AutoCAD DXF file) with output in NAD83. Prospective client (Engineering and PLS firm) wants units in US Survey Feet (N, E, Elevation), but DroneDeploy only exports this particular EPSG in meters. Anyone with experience in getting the right units? I asked the client if they could convert to feet, which they were able to do, but was wondering how I might be able to go about doing this in the future.
 
Couple of questions.

NAD83, what projection? Doesn't Drone Deploy let you choose by EPSG code? You could just choose the EPSG in US Survey feet instead of meters if available.

What is your elevation datum? NAVD88? And how did you get there? GCP's with NAVD88? I only ask because contours is a scenario that most likely would need either Control Points or an RTK/PPK workflow. Non-RTK/PPK drones report in above EGM96 which is not the same as NAVD88.
 
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I was provided GCPs in NAD83 Alabama East State Plane, EPSG 2759.

DroneDeploy doesn't offer US Survey Feet in EPSG 2759...
 
Use Arc Pro to change the units from meters to US Survey Feet on the contours.
I never had the honor of working in HARN. A pretty interesting version of NAD, it went 3D on us.
 
I was provided GCPs in NAD83 Alabama East State Plane, EPSG 2759.

DroneDeploy doesn't offer US Survey Feet in EPSG 2759...
It would be a different EPSG, probably one higher or lower in number is the same state plane but in US FT.

You are right to process in the EPSG you were given GCPs in. If whoever gave you that wanted it in another unit they should have gave you GCP coords in that unit.

I could do all that converting in a few minutes in Carlson Survey, but barring access to that I'm not sure how to do it easily. I use Carlson paired in AutoCAD Map3D and I think the AutoCAD side does have some point manipulation features, but I never mess with them because the Carlson tools are by far more useful.
 
Thanks for the response. I need to look into coordinate conversion options. I'm thinking now that maybe there have got to be tools in addition to this Carlson tool that are stand alone utilities that can convert from one EPSG to another out there...
 
Thanks for the response. I need to look into coordinate conversion options. I'm thinking now that maybe there have got to be tools in addition to this Carlson tool that are stand alone utilities that can convert from one EPSG to another out there...
I'm sure there are I've just never had need of them to look.

This looks promising if you can figure out the input process of the multi point converter. 404 Error: Page Not Found
Code:
https://www.ngs.noaa.gov/NCAT/

One thing that gets tricky is elevation. I frequently see problems resulting from getting ellipsoidal elevations instead of orthometric or vice versa. The only good thing is it's really obvious, in my area it's about 100 ft off if you get it wrong.
 
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Sory I forgot you already have in HARN you just need the contours in feet.

1. Export the DEM/DTM from Drone Deploy
2. Use the Contour Tool to create your contours. At this step you can make the contours in feet or US Ft, whatever your client needs.
2. (Alternative). Use the Times tool to change the elevation in the DEM/DTM to US ft or feet and then Use the Contours tool.
3. Add the point you were talking about, it will be a different feature class since it is a point and not a line.
4. Export back out as a DXF, which I am pretty positive Arc Pro can do.

20 minutes, with the longest amount of time being waiting for Drone Deploy to create the export DEM/DTM raster/tiff. All Arc Pro Tools have info mouse over instructions which make them easy to use.
 
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My practice has always been to leave everything in meters on the processing side including all exports. Autocad Civil 3d will convert it all to US Survey Feet upon import.
 
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So I got a new ERSI Code from the Civil Engineers and this seems to work better. Horizontal is good, but now the elevation is off by 7ft.
Using ESRI 102629, NAD83 Alabama East, units in Feet.

Would I get better accuracy with a M3E? I used the original Mavic Pro.
 
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I am not following you.
Did you reprocess in Drone Deploy with the new EPSG Code?
And how close was vertical previously?

The M3E wouldn't help here, if you are using properly measured and spaced GCP's.
 
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@jaja6009 Sorry, have a couple different ideas going here.
So, yes I reprocessed three different maps with the GCPs using the new EPSG code. I do not know how close they were vertically previously, since I was told they weren't even close horizontally.

I have three different maps from Nadir only images, Crosshatch images (oblique), and a combination of the two. The 7ft difference is from the Crosshatch only capture. I'm waiting for results of the other two to see what works best.

Thanks for info on the M3E. I also have an Air 3, but unfortunately I cannot easily do mapping with it (although I've seen a promising tool in waypointmap.com)

So the Surveyors put the GCPs near the four corners of the map, and the map is about 30 acres. No GCPs in the center.

This is a learning process for me. I appreciate the feedback.
 
Yes, if you gave them the data in the original PCS, it would be off since it has a different origin than the new PCS.

The next problem is, what vertical system were the GCPs in? Orthometric or Ellipsoid. If ellipsoid, then the data will be in ellipsoid. If they were expecting an orthometric then it would be incorrect.

Next, checkpoints are a must in my opinion, and I am surprised the surveyors did not incorporate them along with a center GCP. I am not sure of what will be done with the data, but if you are giving an output of contours I would assume they want vertical.

102629 seems to be supported in Drone Deploy.

If processing with the new 102629 works horizontally, you can use Drone Deploy to perform the Elevation Calibration. Use the elevation from a GCP to set the elevation for the map. This calibration should also apply to the outputted contours and DEM. But this goes back to if the elevations on the GCPs are ellipsoid or orthometric. If ellipsoid, use this tool to gain the undulation and then use this formula to obtain the orthometric elevation H=h-N (h is the ellipsoid value of the GCP and N is the undulation) where you take the ellipsoid elevation of the GCP and then subtract the undulation you get from this tool: 404 Error: Page Not Found

Your project seems like a nightmare for the client, surveyors, and yourself. They should see that the two EPSG codes have different origins and when giving the wrong code would have a large shift.

In the future request the GCPs be in a more friendly PCS based on NAD83 (2011) and ask them to specify if the elevations are in and need to be in orthometric or ellipsoid.
But in some cases, the data will be a local coordinate system, and Agisoft Metashape or Pix4D would be a better software solution.
Drone Deploy may have some incredible tools but starts to lose some luster when flexibility comes into play.
 
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Good information. I'll check with client on what the elevations are for the GCPs.

Yes, I wasn't given enough information to start with, just "can you do contours?", then no EPSG, then the wrong EPSG code.

What is the tool for undulation? A "404 Error: Page Not Found" error is given for your link.

Thanks again.
 
Yes, I wasn't given enough information to start with, just "can you do contours?", then no EPSG, then the wrong EPSG code.

Oh, yeah, that's like a civil Engineering thing. They loathe giving you details. What they are doing is trying to cover up the fact they have no clue how any of this works.
 

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