OnX accuracy
- Thread starter buckbull
- Start date
Gellar
Well-known member
In 2021 I was hunting a unit in Colorado. Through boots on the ground scouting we found a spot that we’d have to skirt private to hunt. In the dark following onx I thought I was 50 yards above the private line. I turned on my headlamp and did a 360 to see the reflective glow of a boundary sign on my right, when I thought it should be on my left. I walked to it to confirm, I was 50 yards on the wrong side of the boundary even though Onx said I was 50 yards on the good side.
Hunting Wife
Well-known member
In a word, yes. Typical and to be expected. Your phone GPS receiver is not as accurate as a survey grade device. The layers on OnX come from a variety of sources, were collected in a variety of datums using a variety of equipment and methods, and are only as good as the devices they were collected with and the methods they were processed with. All OnX really does is compile and display all of these disparate datasets in one place. They really don’t map anything themselves.
No consumer grade application, especially at the scale we’re talking with OnX, is going to be without some level of error. How much error depends on the variables above. OnX is a great tool but people need to realize that it is not, and will never be, the final authority when it comes to accuracy.
No consumer grade application, especially at the scale we’re talking with OnX, is going to be without some level of error. How much error depends on the variables above. OnX is a great tool but people need to realize that it is not, and will never be, the final authority when it comes to accuracy.
Khunter
Well-known member
Onx does not say that is where the property line is. The county govt from whom Onx downloaded gthe data says that is the APPROXIMATE property line.
You have +/- accuracy of the county maintained parcel lines and the +/- accuracy of the phone GPS indication of where on earth the waypoint is located AND the +/- accuracy of the satellite imagery everything is overlain on top of at play.
You have +/- accuracy of the county maintained parcel lines and the +/- accuracy of the phone GPS indication of where on earth the waypoint is located AND the +/- accuracy of the satellite imagery everything is overlain on top of at play.
Bullshot
Well-known member
That last one is always misunderstood. Photo basemaps have all been cut and rendered and or stretched to some degree to be accurately geo referenced based on whatever datum/coordinate systems and projections are in use. They are often damn good. But it's easy to see significant differences from survey, or photo sets taken at different times. There is always some angular distortion from the oblique nature of aerial photos, they do have edge overlap when collected to minimize this, but only 1 point can ever be directly below the lens or sensor be it airplane or satellite. It's just optical physics. Then draping that over a curved landscape to render 3D imagery is another fun source of some error. All in all, its amazing we have it so good given the hundreds or thousands or more of different data sources needed to make modern maps.
Bullshot
Well-known member
And another thing, comparing a point taken by one device to a point taken by another device is meaningless unless you are comparing data in the same system or using a proper conversion. You can set this on your GPS and see what I mean. For example, if you take a point in WGS84 and plot it assuming it will match the "same" one taken in NAD27 or NAD83, etc, you might find yourself on the wrong side of a road or river depending on how you plot it. You need to be consistent, or be aware of the need to convert it back in your processing to the other datum or otherwise properly define it so map software can project it correctly.
Bullshot
Well-known member
Caseknife
Well-known member
I also find that with heavy cover, the OnX point can be off a bit. If you have clear sky view, it is a lot closer. Just did this the other day, I was sitting under a metal awning in front of a business, my blue dot was wandering around out in the middle of the street. I moved our into the street and it showed me in the proper orientation to the buildings on the satellite image.
