Fetch data fields by name

README.md

@@ -28,6 +28,11 @@ allow_loading_unsigned_plugins = spectraphilic-windrose-panel
 
 Restart Grafana service.
 
+Add a panel to your dashboard with the *Windrose* visualization type. Set up the
+query to provide data with `speed` and `direction` fields. The speed can be in
+the unit of your choice (can be set in the settings), while the direction is
+always in degrees.
+
 ## PostgreSQL
 
 Example query for PostgreSQL:
@@ -74,6 +79,22 @@ Set another query for direction:
 This information was provided by @newrushbolt ; for further details see
 https://github.com/spectraphilic/grafana-windrose/issues/18#issuecomment-1007648330
 
+## Flux
+
+Example for InfluxDB v2 filled from SignalK.
+
+```
+from(bucket: "bucket")
+  |> range(start: v.timeRangeStart, stop: v.timeRangeStop)
+  |> filter(fn: (r) => r["_measurement"] == "environment.wind.speedTrue" or r["_measurement"] == "environment.wind.directionTrue")
+  |> filter(fn: (r) => r["_field"] == "value")
+  |> pivot(rowKey:["_time"], columnKey: ["_measurement"], valueColumn: "_value") // put dir and speed values into the same row based on timestamps 
+  |> filter(fn: (r) => exists r["environment.wind.directionTrue"] and exists r["environment.wind.speedTrue"]) // drop rows that don't have both values
+  |> rename(columns: {"environment.wind.directionTrue": "directionRad", "environment.wind.speedTrue": "speedMps"})
+  |> map(fn: (r) => ({ r with  direction: r.directionRad / 3.14 * 180.0 })) // convert to degrees from radians
+  |> map(fn: (r) => ({ r with  speed: r.speedMps / 0.514 })) // convert to knots from m/s
+  |> aggregateWindow(every: v.windowPeriod, fn: first, column: "direction", createEmpty: false) // sample the first row for each window (real aggregation would show fake values in gusty winds)
+```
 
 # Development
 

src/module.js

@@ -122,10 +122,31 @@ class WindroseCtrl extends MetricsPanelCtrl {
         let angles = [];
 
         if (data[0].type == 'table') {
-            // e.g. PostgreSQL
+            // e.g. PostgreSQL and InfluxDB
+
+            let speedCol = null
+            let dirCol = null
+            for (let i in data[0].columns) {
+              if (data[0].columns[i].text == "speed") {
+                speedCol = i
+              }
+              if (data[0].columns[i].text == "direction") {
+                dirCol = i
+              }
+            }
+
+            if (speedCol === null) {
+              console.warn("no `speed` column in data")
+	      speedCol = 1
+            }
+            if (dirCol === null) {
+              console.warn("no `direction` column in data")
+              dirCol = 2
+            }
+
             for (let row of data[0].rows) {
-                speeds.push(row[1]);
-                angles.push(row[2]);
+                speeds.push(row[speedCol]);
+                angles.push(row[dirCol]);
             }
         } else if (data[0].datapoints) {
             // e.g. ClickHouse