Hello all!
Just for background of my knowedge I would call myself an amature enthusiest in surveying. I bought a used theodolite and surveyed a couple of properties. Not for money or any real purpose other than locating pins & lines.
My day job is an estimator for a seeding company. I recently bought an RTK receiver and am trying to used this for measurement of properties for measurement prior to planting and as a map for future maintenance applications.
In my used of the equipment, it seems to be pretty accurate relatively speaking, but I seem considerably off for absolute coordinates.
I am using the SparkFun Express RTK removed link
I am in Indiana so I am using INDOT sponsered INCORS systems for RTK removed link
I have been using SWMAPS for data collection.
If I mark a point, I can get back to it with reasonable accuracy of an inch or two over several days. My concern is trying to locate some of the INDOT benchmarks in my area. The closest I have come to this is 6 feet, but have been as far as 30 feet from the Lat/Lon provided.
Maybe that is as good as I can do with the equipment I have? It will still serve the purpose for me, but if there is a change I can make to have more accurate records, I would appreciate any guidance.
I cannot attach files to this post. When I get to that point, I have data information from SWMaps and the skyplot that may shed some more light on my situation.
Thanks in advance!
What data collector are you using and what software?
I'd have to ask how the record benchmark positions were determined. If they were determined by scaling from a map, or even with recreational grade receivers - which is commonly the case - you are lucky to hit them within 10 feet. IOW, it's not you, it's them.
Are these marks whose published lat-lon data was found with GNSS? Did you get the data from the DOT or elsewhere?
I'm thinking of the NGS data sheets, which have various classes of accuracy. Often elevation marks have very loose horizontal data, so you have to distinguish ADJUSTED vs HH1 vs HH2 vs SCALED.
What data collector are you using and what software?
I have been using swmaps app for Android. I am not very versed in it yet, but I am planing to import into QGIS
I'd have to ask how the record benchmark positions were determined. If they were determined by scaling from a map, or even with recreational grade receivers - which is commonly the case - you are lucky to hit them within 10 feet. IOW, it's not you, it's them.
The benchmarks are reported by the Indiana Dept of Transportation. They are listed as verified and accurate, but at least two of the three have a typo on the benchmark sheet
Are these marks whose published lat-lon data was found with GNSS? Did you get the data from the DOT or elsewhere?
I'm thinking of the NGS data sheets, which have various classes of accuracy. Often elevation marks have very loose horizontal data, so you have to distinguish ADJUSTED vs HH1 vs HH2 vs SCALED.
Indiana Department of Transportation has a published benchmark database. They are supposedly checked but it does not indicate how they are located. It just provides lat/lon and elevation. The three I have checked have all been on bridge/overpass abutments with a bronze plate.
Had a quick look at the Swmaps documentation.
I can find no references to spheroids, geoids, projections or coordinate systems
It would appear to work only in terms of WGS84
My guess is that Indiana DOT use something else - hence the mismatch in numbers
Here is a link to the SW Maps manual. On page 16 it explains how to set a coordinate system for a project. I t also says it defaults to UTM based on the zone it determines you are located in. I'm unfamiliar with Indiana DOT but they likely will say what projection their coordinates are based on. Make sure you are using the same system in SW Maps if you want to match their points.
https://aviyaantech.com/SwMaps/assets/SW%20Maps%20Manual%20V3.0.pdf
I also found this blurb on page 56 indicating WGS84 EPSG 4326 is used if no projection is defined.
To use the ID-X-Y-Z-Remarks format, the project must have a coordinate system
defined. Lat-Lon-Alt uses geographic coordinates in the WGS84 geographic system
(EPSG:4326)
I took a quick look at the IDOT website for benchmarks. The few I looked at if they had a Lat, Long listed it was a tenth of a second or nearest 10' in latitude and 7 to 8 feet in longitude. Not great accuracy. Also, the date on the survey of one with listed L,L was 1989. Doubtful it was a GPS and possibly not even NAD83 conventional surveys.
I'm guessing the L, L is some kinda close number, certainly not something to use as a check; possibly a photo ID#. However, the elevations should be good, you would need to be applying a Geoid Model to make that work.
My I-phone gets me closer than 30' horizontally.
Get on the NGS website and get some good control points, be sure they say they are surveyed points with using GPS. Use them for your checks.
You'd be better off getting a GOOGLE EARTH Lat, Long. number on a Manhole cover.
@lurker 404 - Your link is broken. Try https://aviyaantech.com/SwMaps/docs.html instead
Looks like Google is getting ever worse - it served me up v1.3 of the docs
Can anyone confirm if it works with anything other than Transverse Mercator. I dont have the software to see if it handles Conical projections
They could well be verified and accurate in the vertical component, they are benchmarks after all. Your run of the mill standard benchmark does not usually have a surveyed horizontal location. I'm not familiar with the IDOT benchmark sheets, but most agencies will state accuracies in both vertical and horizontal positions separately.
They are listed as verified and accurate .....
To what level of accuracy?
The accuracy stated that I see is "plot verified".
This is a classic example of someone seeing some data and assuming it's valid for a use it isn't at all valid for.
Humans have types, some never believe anything, some believe everything, then there is the spectrum in-between.
Basically, the database is screaming "DON'T USE THIS DATA FOR HORIZONTAL CONTROL".