A field-grade coordinate instrument built around a map you aim rather than poke.
A field-grade coordinate instrument with six formats, offline measurement and a stamped camera, built around a map you aim rather than poke. Its most interesting code is the test suite: the platform rules that cost me a debugging session each are encoded as invariant tests that fail the build.
Every coordinate app puts a pin under your thumb. You tap, the finger covers the number you came to read, and the fix you get is wherever your fingertip landed, not where you meant. Worse, the moment a surveyor, a driller or a pilot needs MGRS, a stamped photo or an area measurement, the consumer apps stop and the professional ones start at a subscription price with a training course attached. CoordKit had to be precise enough to trust in the field and simple enough to open once, in the rain, with one hand.
A fixed reticle
The map moves under a crosshair that never moves. The map's bottom padding equals the panel height, so the camera's own centre *is* the reticle's point. There is no offset arithmetic anywhere in the codebase, and the coordinate is a continuous edit rather than a discrete guess.
Modes, not routes
Position, Convert, Measure, Compass and Speed swap one panel's contents while the map and the framed point stay put, with no navigation between tools and no state to rebuild when you switch.
Honest precision
The app prints only the decimal places the device's reported accuracy justifies, and names which source an elevation came from, because a barometric altitude and a surveyed height are different claims about the world.
Invariants as tests
Every platform trap that cost a debugging session became a test that fails the build: banned APIs, disposal rules, sheet safe-area, and a cross-check that the code never requests a permission level the Info.plist has no string for.
How it is put together
Sensing
GNSS stream, magnetometer with interference detection, barometer and a terrain-dataset elevation source with named provenance
Coordinate kernel
Decimal degrees · DMS · DD N/S/E/W · UTM · MGRS · Plus Codes, with smart detection on paste in either direction
Measurement
Spherical-model distance and area, live from the framed point rather than from tapped pins
Field recorder
Coordinate-stamped capture burned into the image and its EXIF, plus GPX, KML and CSV in both directions
Invariant test suite
Build-failing tests for banned APIs, controller disposal, sheet safe-area and permission-level/usage-string agreement
The calls worth defending
Treating the readout as the product rather than the map is what makes the fixed reticle possible, which makes a permanent bottom readout possible, which makes tools into modes of that panel instead of separate screens. One decision, and the whole navigation model falls out of it.
A comment saying 'don't use .when here' survives exactly as long as the person who wrote it. Riverpod 3 retries a failed provider, so a failure settles as loading-with-error and `.when` picks its loading branch forever. That is now a test that fails the build if `.when(` reappears in `lib/`. Same for disposing a `TextEditingController` as a local, for sheets that skip `useSafeArea`, and for asking iOS for a photo-library access level with no matching usage string, which does not throw but terminates the process.
The ad SDK was removed outright rather than configured off. A linked ad framework still ships a sample app id in both manifests and still forces a tracking permission string for a prompt the app never shows. Pro is the only revenue, and the privacy label is honest because there is nothing to disclose.
CoordKit and Latitude Longitude Finder share a problem space and a private `coordinate_kit` package, but are independently designed. Two distinct products can rank for the same searches; one product with two skins cannibalises itself and confuses both listings.
What shipped
Aim, don't poke
Fixed reticle over a moving map · six coordinate formats at once
Convert and keep
Smart-detect any input format · saved points with GPX, KML and CSV export
Instruments for the field
Interference-aware compass · speed, trip and moving average
Proof of where you stood
Coordinate-stamped camera with EXIF · accuracy you can defend
Most mapping apps treat the map as the answer. CoordKit treats it as an input device. The camera has bottom padding equal to the panel height, so the camera's own centre is the crosshair's point. There is no offset arithmetic anywhere in the codebase, and a pan is a continuous edit of the coordinate rather than a discrete guess.
That one decision cascades. Because the point is framed rather than tapped, the readout can live permanently at the bottom of the screen without ever being obscured. Because the readout is permanent, the tools can be modes of that panel instead of separate screens. Position, Convert, Measure, Compass and Speed swap its contents while the map, the framed point and the coordinate stay exactly where they were.
A consumer GPS receiver will happily hand you eight decimal places of latitude while being twelve metres wrong. CoordKit refuses to print digits the fix does not support: the number of decimals shown is derived from the accuracy figure the device reports, so the readout degrades visibly when the sky closes in.
Elevation follows the same rule. The app prefers a public terrain dataset, falls back to the device's own altimeter, and tells you which one it used, because a barometric altitude and a surveyed height are different claims about the world.
The most transferable thing in this codebase is not a feature. It is the set of tests that exist purely to stop a specific class of bug from ever returning.
AsyncLoading with an error, and .when picks its loading branch forever. A test fails the build if .when( reappears in lib/.TextEditingController disposed right after await showDialog looks correct and is not. The route keeps rebuilding its subtree through the exit animation, so a still-animating TextField uses a dead controller and throws a frame later, on a device, never in a build log. A test enforces that these are state fields.useSafeArea: true, or a sheet that grows to full height puts its top under the status bar. Enforced.None of these are things a linter catches or a code review reliably remembers. Writing them down as prose would have been a document nobody re-reads. Writing them as failing tests makes the knowledge outlive the person holding it, which is most of what architecture is for.
Six coordinate formats (decimal degrees, DMS, DD N/S/E/W, UTM, MGRS and Plus Codes) with smart detection on input, so pasting anything recognisable works. Distance and area measurement on a spherical model. A compass that flags magnetic interference instead of quietly pointing the wrong way. Speed with trip distance and a moving average. A camera that burns coordinates, elevation and time into the photo and its EXIF metadata, for when a screenshot is not evidence. Saved points with GPX, KML and CSV in both directions.
No advertising, at all. The ad SDK was removed outright rather than configured off, because a linked ad framework still ships a sample app id in both manifests and still forces a tracking permission string for a prompt the app never shows. Pro is the only revenue.
The documents that ship with CoordKit.
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