Live

1 Values

procedure (live-web-number   url             key-line             regexp-pattern            [ error-value             delta-nb-lines])   →   number?

url : string?

key-line : string?

regexp-pattern : string?

error-value : number? = 0

delta-nb-lines : number? = 0

Extracts a value in a web page.

Returns error-value if value not found or internet connection failed.

Example to get wind velocity on a spot location (via winds-up web page)

Which gives

> (live-web-number "http://www.winds-up.com/index.php?p=spots&id=21"

"Aujourd"

"[0-9]+"

-1

3)

Returns wind velocity read as an integer on winds-up web site at 3 lines after that containing "Aujourd" word. Otherwise returns -1.

Another examples:

Wind velocity at Belle-Ile, France via meteociel web site

> (live-web-number "http://www.meteociel.fr/observations-meteo/vent.php"

"Belle-Ile"

"[0-9]+ km/h")

Water level web service

(define (water-level id-station)

(lambda ()

(live-web-number (string-append "http://www.vigicrues.gouv.fr/niveau3.php?idstation="

(number->string id-station)

"&idspc=21&typegraphe=h&AffProfondeur=24"

"&AffRef=auto&AffPrevi=non&nbrstations=3&ong=2")

"<tr><th>Date</th><th>"

"[0-9]+\\.[0-9]+")))

2 Graphics

procedure (live-graph label function rate title) → any/c

label : string?

function : (-> number?)

rate : number?

title : string?

Graphic evolution of value in web page.

An example to display water level at Cavaillon in France (id-station = 142)

> (live-graph "Water level (m)"

(water-level 142)

(* 5 60) ; refresh each 5 minutes

"Cavaillon")

An other example to obtain pressure level in Paris

(define (pressure-paris)

(live-web-number "http://www.station-meteo.com/historique-fr75020-paris/"

"<td>Pression atmosphérique"

"[0-9]+\\.[0-9]+"

-1

7))

With axis scale parameterize

(parameterize ([delta-x (* 12 3600)] ; 12 hours

[delta-y 0.01])  ; 1 %

(live-graph "Level pressure (hPa)"

pressure-paris

(* 5 60)

"Paris"))

Use live-dashboard function to plot multiple web services

procedure (live-dashboard labels functions rate title) → any/c

labels : (listof (listof string?))

functions : (listof (listof (-> number?)))

rate : number?

title : string?

This function displays graphics in rows and columns disposition. Each sublist is a row.

> (live-dashboard '(("Ners" "Besseges"))

(list (list (water-level 38) (water-level 31)))

(* 5 60)

"Water level (m)")

The same but with one function of label parameter

procedure (live-dashboard-one-ft   labels             function             rate             title)   →   any/c

labels : (listof (listof string?))

function : (-> string? number?)

rate : number?

title : string?

Example:

> (live-dashboard-one-ft '(("Paris" "Marseille"))

pressure

(* 15 60)

"Pressure level (hPa)")

(pressure "Paris") and (pressure "Marseille") will be called every 15 minutes.

3 Database

Data displayed in graphs can be saved in real time in a database. For this you can use new-value-event parameter with insert-into-db procedure.

First, describe your dabatase schema in a db-struct structure

struct (struct   db-struct  ( connection         table-name         field-label         field-date-time         field-value))

connection : connection?

table-name : string?

field-label : string?

field-date-time : string?

field-value : string?

Then, use this function in new-value-event handler

procedure (insert-into-db db label seconds value) → void?

db : db-struct?

label : string?

seconds : exact-integer?

value : string?

Example with a table named T_Data containing 3 fields F_Label, F_DateTime and F_Value:

(define my-db (db-struct (odbc-connect #:dsn "BdLive" #:user "" #:password "")

"T_Data" "F_Label" "F_DateTime" "F_Value"))

(parameterize ([new-value-event (lambda (label seconds value)

(insert-into-db my-db label seconds value))])

(live-graph "test" (lambda () 10) 2 "demo"))