I recently bought an RTK Express, and just to get used to this new gizmo I downloaded the corners of my lot from the Boulder County Geospatial Data and entered the lat/lon values into Google Earth. So far so good!
(apparently this system doesn’t like Google Drive links)
You can see in the front of my house, there’s a main sidewalk, and then two paths of stepping stones making a kind of oval. Those stones are easy to see in the map, and easy to find in my yard, so using Google Earth, I clicked on one of the stepping stones and found its lat and lon:
I then took my RTK Express and set it in that same spot. Using SW Maps, it said it had a lat error of 290 mm and a lon error of 260 mm which is awesome.
Looking at the raw output using SW Maps, the lat/lon were bouncing around in the least significant 2 or 3 digits. I wrote down 6 lat and 6 lon values, and then entered those points into Google Earth. The 6 points are nicely bunched up, but they’re 89 cm away from the actual location, which is about 3x what the RTK said it was doing.
If I understand you correctly: you’re obtaining a lat/long from dropping a pin on a thing (oval rock) in google maps, then walking outside and expecting the rock to have the same lat/long? I’m not surprised they don’t line up. Imagery is closely aligned, but not nearly as accurate as the RTK products.
Imagine this: you’re a low earth orbit satellite about 50 miles above the earth. You take a bunch of photos that then have to be stitched together and then aligned to the surface of the earth. Google (and really any imagery) is close, but off by, I dunno, easily meters, but not 10?
Just because I think it’s interesting, checkout the recent google maps image of SparkFun:
Note the ice that was on the camera lens that google’s algorithm’s didn’t pick out because of our white roof.
What I’m more interested in is repeatability. Can you go out to the same rock day after day and hit the same lat/long? It doesn’t sound like you’re using the device in RTK Fix mode yet, but that’s when the fun really begins.
Please keep asking questions if something doesn’t make sense!
RTK Fix mode sounds really cool, but it sounds like it requires two things - (1) a second RTK Express, and (2) a point whose location is known with great accuracy. Right?
I want to play some more with the RTK Express, and seeing how well it lines up with various sources I find online. For example, according to https://www.gislounge.com/what-is-the-p … ll-use-it/, “Surveyors were sent out by the United States Geological Survey (USGS) to place brass markers on the ground at the corners of each PLSS section” and according to randymajors.org, the southeast corner of a section is right next to the SparkFun HQ (at the corner of Hwy 52 and 79th st):
So I should be able to drive up to that intersection, find the brass cap, set my RTK Express on top of the brass cap, and get lat/lon readings that are really really close to the values reported by earthpoint?
It seems like your forum software is kind of a mess. There’s a row of 4 boxes at the bottom of the page that should contain links to other posts. I pick one at random (From 30 Dec, “Lasagna on me this time OK?”) and click on it - and it brings me right back to my same post.
RTK Fix mode sounds really cool, but it sounds like it requires two things - (1) a second RTK Express, and (2) a point whose location is known with great accuracy. Right?
So I should be able to drive up to that intersection, find the brass cap, set my RTK Express on top of the brass cap, and get lat/lon readings that are really really close to the values reported by earthpoint?
This is a very cool approach but I’m not convinced there is a monument at the corner, and/or it may be in the middle of the intersection However, just down the road (and up the hill) you can use a known marker: https://rtklibexplorer.wordpress.com/20 … -d302-rtk/
I found Tim’s (rtklibexplorer) posts years ago when I started designing the RTK products, and always wanted to replicate it once I got the hardware to a ready-enough place but forgot about this particular experiment until you jogged the memory loose. I’ll see if I can go visit the Somerset monument later this week. Note: SparkFun operates a public correction source called bldr_SparkFun1 that you can view on rtk2go.com:2101 (of course it’s down as I write this but I’ll kick the server when I’m in the office next) so well within the 10km baseline needed for good RTK. I’ll be interested to see if our base’s PPP sourced location correlates/matches the NGS marker.
It seems like your forum software is kind of a mess.
Indeed. I’ll see if I can get someone to do some cleanup.
I wandered up to that marker you found in the blog post, set my RTK Express antenna right over the spot, and after letting it sit for a minute or two recorded some readings.
That latitude varied between 40.08746502 and 40.08746620, and the longitude varied between -105.15048816 and -105.15049261. Those points are all within 30 cm of each other which is awesome!
However, those points are all about 175 cm ENE from the actual point, according to the NGS Data Sheet.
I can’t figure out how to get the “easy-to-use tool from the U.S. National Geodetic Survey that will translate from one coordinate system to another” to work, am I running into the difference between NAD83 and WGS84?
However, just down the road (and up the hill) you can use a known marker: 
