I performed a localization in Emlid Flow w/ Survey on a rectangular piece of ground that covers about 100 acres and is about 3,700 feet long by 350 feet wide. Five years ago I set fifteen ground control points across the property and was able to relocate four of them last week for the initial localization. The control points are in a local coordinate system relative to a flat, level horizontal plane established using a total station. Those four points are located roughly toward one corner of the 100 acre rectangle. The localization using the four “Measured” points had good accuracy with very small errors (0.041’ horizontal and 0.039’ vertical). After applying the localization, I used Stakeout to locate and “Measure” another four points near the other end of the property. What I noticed was that, during Stakeout, I could precisely locate each stakeout point horizontally, but vertically there was increasing vertical error the farther I got from the four points used for localization (e.g. about 1.5’ vertical error at the stakeout point 2,000’ away from the localization area). I assume this is due to the Localization creating an inclined plane. However, the Localization Preview screen (in the Inclined Plane section) didn’t seem to indicate that the Localization contained any slope (Preview Results showed 0.0 ppm for both East and North). What am I missing here? When I located the four additional control points (using Stakeout) and “Measured” them to include them in the Localization, the sloping plane seemed to flatten out very nicely and I was able to go to any of the 15 control points (or hundreds of survey points from five years) with ago very little vertical difference from the old coordinates. Perhaps I don’t fully understand what’s going on in Localization, but it appears to me that Localization calculates and applies a (potentially sloping) plane based on whatever points are used in the Localization and, using only three or four Control/Measure pairs over a small area runs the risk of creating a sloping plane that could translate to very large vertical errors at points distant from the Measure group of points. Is this correct? Is there a setting in Localization that forces it to create flat, level, horizontal plane similar to what a total station will create? Thanks.
I dont really use Flow, but other survey software… but from what i understand, to avoid an inclined plane, ONLY hold to 1 vertical, not ALL of them when localizing. Typically you can still measure them all, evaluate your verticals and only use the BEST one to hold to, unchecking or not using the rest of the verticals with high residuals.
That makes way too much sense. Such a simple solution. I certainly over-thought the problem. Thank you!!
We tend to ALL do. 
I’ll have to look again… but I think there is a warning in Flow about selecting / holding to more than 1 vertical will cause a inclined plane? Cannot remember… and if not, probably should have this warning in red.
Using 4 points horizontal and vertical on one side of the site isn’t an accurate way to relocate points 3700’ on the other side of a project and to expect great accuracy recovery. If I did find them, I would take their stated accuracy in the software with a grain of salt.
As @timd1971 said, you are constraining your localization to a few points with supposed 0.04’ accuracy horizontal/vertical then transferring that accuracy 3700’ on the other side of the site. Imagine using a terrestrial traverse (which you used to begin with) to the other side of the site expecting the same error accuracy… it won’t happen. Was the original traverse net a closed loop and balanced or just an open traverse ?
Using your control marks as “fixed” for the rest of the site is not very wise. Use at least 3-4 points scattered throughout the site with holding 1 vertical component and then compare. You’re magnifying your found points error exponentially across the site.
Hi Steve, Four points for a control point is good enough, however, we recommend spreading the points evenly across the entire area for localization.
We have this document about localization. I suggest spreading the control point and checking if the vertical error decreases.
To PREVENT AN INCLINED PLANE do not hold to more than 1 vertical.
I discussed this case with the team. Since your control points are clustered only on one side of your survey area, when you use more than two vertical control points, the plane tends to be inclined, and the error increases as it gets farther from the control point.
If you can distribute a control point evenly in your work area, like on the four sides, you can use more than two vertical points. However, if it’s clustered on one side, then just use a maximum of two vertical points for calculation.
For now, we don’t have this feature to choose whether to use a flat or an inclined plane, but we will add yours as a feature request.
???
It’s already there.
If you want FLAT. use 1 vertical or NONE. (Check to hold just 1 vertical or uncheck all vertical)
If you want INCLINED PLANE, use 2 or more verticals.
If anything this needs a NOTE in red or something warning about an inclined plane may be created if using 2 or more verticals, simple as that.
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I think Tim’s suggestion to add some sort of warning feature to Emlid Survey indicating a sloped plane during Localization has a lot of merit. I’ve applied, with good success, his previous suggestion to look at all of the Localization vertical errors of the paired points and then unchecking all but one vertical.
I especially like the ability in Emlid Survey of being flexible enough to “Measure” only a few easy-to-find control points for a preliminary Localization, then use Stakeout to find and “Measure” additional control points, and then finally re-execute Localization on all of the “Measured” points. It would be helpful to be able to perform a preliminary Localization on only two “Measured” control points rather than needing to "Measure’ three control points. Sometimes that third point is difficult to find. I come from a Trimble robotic total station background where it requires only two known points to perform what it called a “Resection”.
Thanks.
That is bare minumum. Best to use more as you know to perform a proper resection.
As far as what I have described for localization, this is pretty standard in most reputable professional survey software.
Emlid, if not already, should get a hold of all the major survey software or at least most poupular and start replicating and knocking these standard (and expert) features off of their to-do list. Going to obviously need more man-power at this rate to compete.
Tim, I’m curious what other survey software you’ve had success with using Emlid hardware (e.g. the Reach RS3). Emlid Flow has been great to get started on, but I’d like to find an Android program to use on a tablet that allows me to bring in a base map or a dxf drawing for a background while doing stakeouts (as well as more COGO functions). As a point of reference, I’ve been using the Trimble TSC3 for years, and the TSC5 more recently, but I barely scratch the surface of what those can do and don’t need all of that power. Thanks.
My all-time favorite is MicroSurvey FieldGenius for WINDOWS as it supports Leica robotic total stations which i need. (Trimble stripped support from it years and versions ago) The Android version is very nice too, but NO “Robotic” total station YET. (Been over a year or so of that promise?) MicroSurvey, like Emlid, it’s taking EONS for full survey feature implementations in the Android version. Ongoing Work In Progress (WIP) I don’t have YEARS to wait.
You may find the Android version suites you just fine though. Get the FULL FEATURED 30 point limit Windows demo and not fully fearured Android demo and try them. They are great.
Many here use them along with Flow.
There are MANY MANY chinese apps and others also. Do a search of the emlid community… but the most popular seems to be variations of SurPad due to features and very low cost. I dont use any of them as no support for robotic total stations.
Trimble Access is probably the best period though… $$$$$$$$$$$$$$$$$$$$$$$$$ but apparently only works with their own equipment for obvious reasons. Locked down pretty good dont even think can connect a NMEA receiver to it.
Yes, we do have an option to choose how many horizontal and vertical points we want to use. For now, we can only use one or two control points for the flat plane.
The feature request is to have an option to choose between a flat and an inclined plane. With this feature, we would be able to use three or more points to calculate a plane, ensuring it remains flat if needed.
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