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Corpscon6 – geoid 18 files
Posted by arkansas90 on August 10, 2023 at 2:01 pmDoes anyone know where I can find GEOID18 files for use with Corpscon6? These would be BIN files and a Text file. We have a few guys in the office that are still using Corpscon6 rather than NCAT. They are currently setup with GEOID12b, but we are now using GEOID18 for all field data collection (and have been for a while now). Thank you in advance!
OleManRiver replied 9 months, 3 weeks ago 6 Members · 11 Replies 
11 Replies

Does anyone know where I can find GEOID18 files for use with Corpscon6? These would be BIN files and a Text file. We have a few guys in the office that are still using Corpscon6 rather than NCAT. They are currently setup with GEOID12b, but we are now using GEOID18 for all field data collection (and have been for a while now). Thank you in advance!
Have you tried here;
https://geodesy.noaa.gov/GEOID/GEOID18/downloads.shtml

@bobwesterman That had exactly what I was looking for, thank you! For some reason I had it stuck in my head that I was looking for a download specific to Corpscon.

We have a few guys in the office that are still using Corpscon6 rather than NCAT
I liked CORPSCON, but it was last updated nearly a decade ago, and has since been deprecated. The tools under the hood of NCAT have been updated a few times since then, so the computations will definitely give different (albeit not likely large) answers.
“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” Neil Postman 
We have a few guys in the office that are still using Corpscon6 rather than NCAT
I liked CORPSCON, but it was last updated nearly a decade ago, and has since been deprecated. The tools under the hood of NCAT have been updated a few times since then, so the computations will definitely give different (albeit not likely large) answers.
I haven’t needed to use Corpscon in quite a while, and so haven’t really taken the time to look into NCAT.
Can it be run locally, or is it only a web based application?

I haven’t needed to use Corpscon in quite a while, and so haven’t really taken the time to look into NCAT.
Can it be run locally, or is it only a web based application?
For NCAT, there are online computations, a downloadable program, plus a web service that can be integrated into other applications:
https://www.ngs.noaa.gov/NCAT/
Yeah, I don’t need to run conversions very often any more. Maybe vertical occasionally, but for that invariably using a datasheet is better and more reliable than NCAT/VDatum.
Not to mention that for horizontal, TBC can do all the NAD83/NAD27 conversions that I’d ever need, and vertical is a matter of just holding a mark.
“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” Neil Postman 
@rover83 Apart from occasionally converting NAD27 coordinates to NAD83, we mainly use Corpscon for calculating a combined scale factor. On plats, we list the combined scale factor at a particular point because we show grid distances.
This brings up a few other recurring questions I’ve had:
(1) How do you get a combined scale factor from NCAT? It gives me an “N/A” return.
(2) Is there any easy way to get a combined scale factor, other than NCAT or Corpscon?
(3) Our state standards require boundary distances to be horizontal ground distances; however, we show grid distances and list the combined scale factor. We primarily do boundary using GPS, with our data and drafting in the SPCS. Other than manually calculating ground distances using the combined scale factor we calculated at a single point (this point usually being the POB), where ground distance is equal to grid distance divided by the combined factor, how else would we show ground distances?
When I’ve asked other surveyors, they have said that because the combined scale factor is so close to 1, the difference between ground and grid distances is minimal, so they don’t worry about converting to ground distances.

(1) How do you get a combined scale factor from NCAT? It gives me an “N/A” return.
If you’re getting an N/A, you are probably only inputting the latitude/longitude.
To get a combined factor, you also need an ellipsoid height.
Select “horizontal + height” and make sure you enter the ellipsoid height of the point of interest.
(2) Is there any easy way to get a combined scale factor, other than NCAT or Corpscon?
Yep. Dozens of commercial software packages can do it. Most field software can do it too. I’m not sure what field and office programs you are running, but I’d lay odds that whatever postprocessing software you have can do the computations. When we process our data in TBC, we can query all any point’s scale factor(s) and decide which one we want to use.
If you really want to DIY it, the equations aren’t difficult either. An Excel spreadsheet with a few formula cells could do it.
(3) Our state standards require boundary distances to be horizontal ground distances; however, we show grid distances and list the combined scale factor. We primarily do boundary using GPS, with our data and drafting in the SPCS. Other than manually calculating ground distances using the combined scale factor we calculated at a single point (this point usually being the POB), where ground distance is equal to grid distance divided by the combined factor, how else would we show ground distances?
Pick the desired combined scale factor (use a primary control point, or average of all points, or whatever you want) and scale your data by its reciprocal. Again, most postprocessing software can do this on the fly. At the most basic, one could take a CAD drawing file and apply the scalar to all entities.
That way the map is at least showing “ground” distances, and the CSF can still be listed for reference, but the reader does not have to manually scale distances to get to ground.
When I’ve asked other surveyors, they have said that because the combined scale factor is so close to 1, the difference between ground and grid distances is minimal, so they don’t worry about converting to ground distances.
That’s possible, assuming your project falls in the right location at the right elevation and is the right size. I don’t know if I would believe a surveyor claiming that all of their projects can be classified as such, unless they are only working in a very specific area.
“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” Neil Postman 
You could use NGS Data Explorer to go to your project location, then perform a radial search near where you want the CSF. Assuming some marks are found, you can then go to list view and see what type of control the found points are. If there are horizontal points, pick one and look at the datasheet. It should have the CSF for that point right on the datasheet.

An example of a large CF yielding a halfmeter difference in a 1 kilometer line is at the Telluride, CO airport.
See attached data sheet for a point located at the highest elevation airport with commercial flights.

@arkansas90 NCAT will give you all information you need if the input information is put in. So ellipsoid ht maybe elevation would work. It needs the ellipsoid to compute the ellipsoid factor to create the combined factor. You can have multiple points csv or text file and output your desired information in a excel spreadsheet or csv etc or just one point. So if you are getting N/A it’s because no input information to compute.

I believe Carlson cad can do all of this . I know TBC can. I am getting plat together now all on grid state plane. I can list distances by ground or grid on the auto line label. It will also generate a CF at each point i can easily use to compute an average as well. Just depends on my project size and location how I approach which method to use. Unfortunately if I am on state plane it computes the acreage at grid. So i use the ngs published manual I think 235! I then use my CF to correct the auto label. From the square feet etc. It was a good published document that when NAD27 was used they had everything a Land Surveyor needed to do boundary work on the grid all the corrections and formulas. I am doing the whole school thing with kids. Two kids two different schools and lots of kids. But i will try and post that ngs doc tonight or tomorrow here. I had it saved look through this its a good one just remember we use ellipsoid factor not elevation factor now to get to combine factor
https://geodesy.noaa.gov/library/pdfs/Special_Publication_No_235.pdf
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