Does a GPX file record GPS accuracy for each point?

The short answer

A GPX point can carry accuracy-related fields — hdop, vdop, pdop, sat, fix — but every one of them is optional, and the overwhelming majority of tracks recorded on a phone simply omit all of them. Open a GPX file exported from a typical hiking or running app and you will usually find latitude, longitude, elevation and a timestamp per point, and nothing else.

That is not a sign of a corrupted or incomplete file. It means the app never had a number of the specific kind those fields expect, so it left them out rather than writing something misleading into a tag with a defined meaning.

What the schema actually sets aside for this

GPX 1.1 lets a track point carry, among other optional elements, hdop (horizontal dilution of precision), vdop (vertical dilution of precision), pdop (position dilution of precision), sat (the number of satellites used for that fix) and fix (the type of fix — 2D, 3D, DGPS and so on). None of them are required. A point with only a latitude and longitude is just as valid a GPX point as one carrying all five.

These fields are a holdover from an earlier generation of GPS hardware — dedicated handheld units and marine or aviation receivers — where the chip computing your position could also report exactly how strong the satellite geometry was at that instant. A low dilution-of-precision number meant the satellites in view were well spread across the sky; a high one meant they were clustered together, which weakens the fix. Writing that number alongside the coordinate was a natural thing for those receivers to do, so the format made room for it.

Why a phone describes accuracy differently in the first place

A phone does not hand its apps the raw dilution-of-precision figures a dedicated GPS chip might compute internally. iOS reports location accuracy as a horizontal accuracy value in metres — in effect, a radius around the reported point inside which the true position is likely to fall. That is a genuinely useful number for an app to show live while recording, but it is not the same measurement as HDOP, and there is no direct conversion from one to the other. An app cannot write a meaningful hdop value into a GPX point because it was never given one to begin with; it only has a distance in metres, and the format has no standard field built for that particular figure.

So the gap is not an oversight in how recording apps export their data. It reflects a real difference in what modern phone location APIs report compared with what the classic GPX accuracy fields were designed around.

What this actually costs you

Less than it sounds like. A recording app already uses whatever accuracy information it has while a hike is underway — deciding whether a fix is good enough to log, smoothing out an obviously bad reading, waiting a moment longer for the receiver to settle before it starts a track. By the time a point makes it into the saved route and later into an exported GPX file, that filtering has already happened. The file you get is the set of points the app was willing to stand behind, not a raw feed of every reading together with a confidence score attached to each one.

A GIS tool or a research workflow that specifically wants a dilution-of-precision figure for statistical filtering is really asking a question phone-based tracks were never built to answer. That is a legitimate use case for the kind of dedicated GPS hardware the field was designed for, and one a general fitness- and outdoor-recording app was never trying to serve.

Things that trip people up

• Assuming an empty hdop field means the track is untrustworthy — it usually means nothing more than that the file came from a phone, since the field is optional and phone apps have no matching value to put there.
• Expecting a mapping or GIS tool that asks for a dilution-of-precision figure to accept a phone-recorded GPX file the same way it accepts one from a survey-grade receiver — the field being absent is a difference in what the recording hardware reports, not a defect in the file.
• Confusing the live accuracy figure shown on screen while recording with something that ends up written into the exported file — the two are related in purpose but are not always the same field, and most consumer apps do not carry the on-screen number through into the GPX export at all.
• Assuming every recording app leaves these fields out for the same reason — some simply never had the data; a handful of dedicated GPS units genuinely do have proper dilution-of-precision figures to write, because their chips compute one directly.

Where TrailCam fits in

TrailCam exports a route as GPX 1.1 with the fields every reader in this series of guides actually depends on — latitude, longitude, elevation and a timestamp for each point. It does not attach a dilution-of-precision figure, for the same reason described above: that is not the kind of accuracy number an iPhone's location system hands an app in the first place. Export is part of the optional TrailCam Pro upgrade; the app itself is free to download.