Update docs

correctedforecaster/internal/server/server.go

@@ -148,6 +148,8 @@ func (s *Server) correctWithBetterTopography(request *internalprotocol.GetForeca
 	}
 
 	altitudeDiff := *modelAltitude - realAltitude
+	// Only correct when the altitude difference exceeds ±100 m. Smaller gaps are
+	// within the noise of the model grid and not worth adjusting.
 	if altitudeDiff < -100 || altitudeDiff > 100 {
 		correction.UpdateTemperature(interpreted, altitudeDiff)
 		correction.UpdateDewpointTemperature(interpreted)

healthz/internal/health/probe.go

@@ -46,6 +46,10 @@ func NewProbeResult(serviceProblems, dataProblems map[string][]string, maxfailed
 func runProbe(conf *config.ProbeConfiguration) ProbeResult {
 	log.Println("Perform probe...")
 
+	// serviceProblems and dataProblems are tracked separately so that health can be
+	// reported on two independent dimensions: service (any location failing means the
+	// API itself is broken) vs. data (a configurable number of locations may have stale
+	// or missing data before the data dimension is considered unhealthy).
 	serviceProblems := map[string][]string{}
 	dataProblems := map[string][]string{}
 

jsonfrontend/internal/server/server.go

@@ -79,6 +79,9 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		metrics.OutsideAllGrids.Add(1)
 		return
 	case internalprotocol.ForecastStatus_PointTooFarAway:
+		// The point is within a grid's bounding area but too far from any grid cell.
+		// Return 200 with a GeoJSON error body rather than 4xx so that clients receive
+		// a structured response with location context instead of a plain HTTP error.
 		doc = encode.EncodeError(data, "no data at the given location")
 		metrics.PointTooFarAway.Add(1)
 	default:
@@ -193,7 +196,8 @@ func getParam(q url.Values, name string, from float32, to float32) (float32, err
 }
 
 // expires returns a randomized time.Time for use as a value to the Expires header.
-// Maximum value is current + maxOffset seconds.
+// The expiry is randomly drawn from [0.8×maxOffset, maxOffset) rather than being
+// a fixed value. This spreads cache invalidation across clients to prevent stampedes.
 // Returns current time + 1 minute if maxOffset <=0.
 func expires(current time.Time, maxOffset int) time.Time {
 	if maxOffset > 0 {

rawdataforecaster/README.md

@@ -1,53 +1,18 @@
-# Simple Forecaster
+# rawdataforecaster
 
-Serves unmodified data from a forecast. The term 'simple' refers to the data not having been processed by forti.
+Serves raw (uncorrected) forecast data over gRPC from a blob store (Azure, S3, or local `file://`) in the [forti-internalformat](https://github.com/metno/forti-internalformat) format.
 
-## Serving data
+## Loader strategies
 
-```mermaid
-graph LR;
-server --> forecast;
-forecast --> dataset;
-dataset --> index;
-dataset --> values;
-```
+The `loader.type` config key selects how forecast data is held in memory:
 
-Four components are mainly involved in serving data: 
+| Type | Behaviour |
+|---|---|
+| `memory` | Downloads the full grid blob at startup into CGo-allocated memory (bypassing GC pressure). Zero I/O at query time. Capped by `max_size_gib`. |
+| `blob` | Downloads nothing upfront; issues a byte-range read per query (2 s timeout). |
 
-### server
+Use `memory` when latency matters and the dataset fits in RAM; use `blob` otherwise.
 
-Handles incoming grpc requests, including protobuf serialization.
+## Native dependencies
 
-### forecast
-
-Determines what is the correct group (and version) to serve data from. Forwards requests to the relevant `dataset` handler.
-
-### dataset
-
-Each object of type `dataset.Dataset` serves data for a single area/version. They maintain a list of grids for its area. A grid is a unique collection of latitude/longitude pairs within a single area. They exist because different parameters may have different grid resolutions.
-
-Handles requests for a given latitute/longitude pair. For each grid, lookup the correct index from `index`, and find relevant data from `values`.
-
-### index
-
-Handles lookup from latitude/longitude to a grid index.
-
-### values
-
-A collection of all data having the same area and grid id. 
-
-Provides a `Reader` interface, for looking up data with a given index. The index is provided by the `geo` component. There are several implementations of this interface.
-
-## Loading data
-
-`forecast` component contains a function, `Forecast.update`, that is called periodically in a goroutine. It checks a blob store for updates, and loads data if needed, by calling `dataset.Download`.
-
-## Other modules
-
-### internal.health
-
-Provides grpc healthcheck, meant for kubernetes readiness probe.
-
-### pointdata
-
-Defines internal data format. Its placement reflects that several modules in various places in the hierarchy needs access to this.
+The geographic index uses [s2geometry](https://github.com/google/s2geometry) and [PROJ](https://proj.org/) via CGo. These are pre-installed in the devcontainer; building outside it requires both libraries.

rawdataforecaster/cmd/lookup/main.go

@@ -15,7 +15,9 @@ import (
 func main() {
 	latitude := flag.Float64("lat", 59, "latitude to query")
 	longitude := flag.Float64("lon", 11, "longitude to query")
+	altitude := flag.Float64("altitude", -1, "altitude to query; set to 0 for sea level, default -1 means not set")
 	address := flag.String("address", "localhost:5052", "Server to connect to")
+	parameter := flag.String("parameter", "", "Only show data for the given parameter")
 	flag.Parse()
 
 	// Set up a connection to the server.
@@ -33,6 +35,12 @@ func main() {
 		Latitude:  float32(*latitude),
 		Longitude: float32(*longitude),
 	}
+	if *altitude != -1 {
+		request.Altitude = &internalprotocol.Altitude{
+			Override: true,
+			Value:    float32(*altitude),
+		}
+	}
 
 	forecast, err := c.GetForecast(ctx, &request)
 	if err != nil {
@@ -46,6 +54,9 @@ func main() {
 	fmt.Printf("updated at: %v\n", forecast.ForecastMeta.UpdatedAt.AsTime())
 	fmt.Printf("next update: %v\n", forecast.ForecastMeta.NextUpdate.AsTime())
 	for _, meta := range forecast.ParameterMeta {
+		if *parameter != "" && meta.Parameter != *parameter {
+			continue
+		}
 		fmt.Printf("%s (%s):\n", meta.Parameter, meta.Units)
 		for i, t := range meta.Times {
 			value := forecast.Data[i+int(meta.SliceFrom)]

rawdataforecaster/internal/server/forecast/dataset/index/geo.go

@@ -29,6 +29,10 @@ type indexID struct {
 	GridID  string
 }
 
+// idCache maps a (area, version, gridID) triple to the MD5 checksum of its lat/lon data.
+// checkSumCache maps that checksum to a shared GeoMap (the s2geometry spatial index) with
+// a reference count. Together they allow datasets with identical grid geometry to reuse
+// the same GeoMap across version updates, avoiding an expensive rebuild.
 var idCache map[indexID]string
 var checkSumCache map[string]*cachedMaps
 var cacheMutex sync.Mutex