My base station is set on NAD83 (2011) monuments. I am putting out ground control points for a drone flight. My image processing software (webODM) requires WGS84 (G1150) coordinates in either Lat / Long or UTM Z12N.
Do I need to transform the NAD83 coordinates of my ground control points to WGS84 to produce accurate orthomosaics and 3-D models from the drone imagery?
Hello Mark,
Yes, you should perform a coordinate transformation between NAD83 (2011) and WGS84 (G1150) for your ground control points when using them in WebODM. This is important to ensure accurate ortho-mosaics and 3D models from your drone imagery.
Datum Difference: NAD83 (2011) and WGS84 (G1150) are both modern geodetic datums, but they have slight differences in terms of their origin, orientation, and reference ellipsoid. These differences can cause discrepancies in coordinates when working with data across the two datums.
Coordinate Reference Frames: NAD83 (2011) and WGS84 (G1150) are related but not identical coordinate reference frames. While they are close, there can be several centimeters of difference between coordinates in the two datums.
When you’re collecting or using data from one datum (NAD83) and need to work in another datum (WGS84) due to software requirements, it’s important to perform a datum transformation. This involves not only re-projecting the coordinates but also accounting for the differences in datum parameters.
In your case:
For Ground Control Points: Convert the NAD83 coordinates of your ground control points to WGS84 (G1150) coordinates using an appropriate transformation method. This could involve Helmert transformation parameters or using specific software or tools designed for this purpose.
Image Processing: When you input these converted WGS84 (G1150) coordinates into WebODM, it will then properly align the imagery with the accurate ground control positions.
By performing this transformation, you ensure that the accurate geographic positions of your ground control points are used for the ortho-mosaics and 3D models, resulting in improved georeferencing and accuracy in your final outputs.
Thank you for your response. The transformation is very confusing and I am having difficulty in finding out how to do the transformation. I am in Utah (UTM Zone 12N). Can you recommend any software solutions. In QGIS the transformation gives a warning that it will only be accurate to 1 meter. The NOAA sites are mystifying because they state they do the conversion but then there does not appear anyway to do them. Some early literature states that the datums were very similar but because of tectonic plate movement they diverge as time increases. Any suggestions you have would be most appreciated.
That is the site that confused me.
There is no direct transformation to WGS84.
NAD83 (1986) used the same ellipsoid as WGS84 (original). But there was still an accuracy of ± 1 meter.
Are you aware of a better match with the NAD83 options available at this site?
https://geodesy.noaa.gov/TOOLS/Htdp/Htdp.shtml
Don’t worry about the conversion caution statement. That’s political.
It does everything. You have to make sure you select the correct settings and use the correct input data. There are many other options including internal survey software features and probably many other websites.
Also NAD83 uses GRS80 which is very similar to WGS84 as @texasaerialimagery mentioned, but slightly different, but probably not enough to worry about.
Hi Mark,
Sorry for my late response. Have you managed to convert your coordinates to WGS84? Since it’s can perform a Time-Dependent transformation, I believe @jbonde002 solution should be precise enough for your project.
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