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Define the date period to download

Stijn Van Hoey

2023-05-05

Source: vignettes/define_date_periods.Rmd
define_date_periods.Rmd

Introduction

When downloading time series with the get_timeseries_tsid() method, the ts_id argument provides the link with the variable, location and frequency of the time series, but not the extent/period to download.

The time period to download is defined by a combination of the arguments from, to and period. The usage is similar with the VMM documentation for the API itself. The main difference is that the wateRinfo package uses existing R functions to interpret the date strings given by the user before sending these to the API (as a formatted string according to %Y-%m-%d %H:%M:%S).

This vignette aims to briefly explain how to define the arguments.

Which combinations?

In order to define a period, a start and end date is required. Defining all three will result in an error, but any combination of from/to, from/period and to/period is allowed. Moreover, if only period or from are defined, the waterinfo.be API will automatically define to as the current time. Hence, defining the last x days/months/years/… can be achieved by only using the period option.

How to define the from/to dates

The package will both except valid date strings as well as valid date objects (POSIXct, POSIXt) as input for the from and to arguments. When using a string value, it can be defined on different resolutions:

  • “2017-01-01 11:00:00”
  • “2017-01-01”
  • “2017-01”
  • “2017”

According to the lubridate package, these orders are accepted: ymd_hms, ymd, ym, y. As a result, also "2017/01/01", "2017 01 01" or "20170101" are valid date string inputs. Make sure the order of year-month-day is respected. For example, "01/01/2017", "01-01-2017" and "01-2017" are NOT valid.

How to define the period

The period string provides a flexible way to extract a time period starting (in combination with from) or ending (in combination with to) at a given moment. Moreover, by using only the period as argument, it will cover all cases where one is interested in the last x days/months/years/….

Some examples are:

  • P3D : period of three days
  • P2Y : period of 2 years
  • PT6H : period of 6 hours
  • P2DT6H : period of 2 days and 6 hours
  • …

In general, the period string should be provided as P#Y#M#DT#H#M#S, where P defines Period (always required!) and each # is an integer value expressing the number of…. The codes define a specific time interval:

  • Y - years
  • M - months
  • D - days
  • W - weeks
  • H - hours
  • M - minutes
  • S - seconds

T is required if codes about sub-day resolution (day, minutes, hours) is part of the period string. Furthermore, D and W are mutually exclusive.

More examples of valid period strings are:

  • P1DT12H : period of 1 day and 12 hours
  • P2WT12H : period of 2 weeks and 12 hours
  • P1Y6M3DT4H20M30S: period of 1 year, six months, 3 days, 4 hours, 20 minutes and 30 seconds

Examples

When interested in irradiance (15min frequency) data, the following stations provide time series:

get_stations("irradiance")
##      ts_id station_latitude station_longitude station_id station_no
## 1 78845042         51.27226          3.728299      12207   ME03_017
## 2 78879042         50.86149          3.411318      12209   ME05_019
## 3 78947042         51.20300          5.439589      12213   ME11_002
## 4 78913042         50.73795          5.141976      12211   ME09_012
## 5 78862042         51.24379          4.266912      12208   ME04_001
## 6 78896042         50.88663          4.094898      12210   ME07_006
## 7 78930042         51.16224          4.845708      12212   ME10_011
##              station_name stationparameter_name parametertype_name
## 1            Boekhoute_ME                   Rad                 Rn
## 2              Waregem_ME                   Rad                 Rn
## 3             Overpelt_ME                   Rad                 Rn
## 4 Niel-bij-St.-Truiden_ME                   Rad                 Rn
## 5              Melsele_ME                   Rad                 Rn
## 6           Liedekerke_ME                   Rad                 Rn
## 7            Herentals_ME                   Rad                 Rn
##   ts_unitsymbol dataprovider
## 1          W/m²          VMM
## 2          W/m²          VMM
## 3          W/m²          VMM
## 4          W/m²          VMM
## 5          W/m²          VMM
## 6          W/m²          VMM
## 7          W/m²          VMM

Focusing on the data of Herentals, the ts_id to use is 78930042. We have different options to define the period to get data from:

  1. data about the last day, using period only:
irr_lastday <- get_timeseries_tsid("78930042", period = "P1D")
ggplot(irr_lastday, aes(Timestamp, Value)) +
    geom_line() + xlab("") + ylab("irradiance (W/m2)")

  1. data about the last 12 hours, 30 minutes, using period only:
irr_lasthours <- get_timeseries_tsid("78930042", period = "PT12H30M")
ggplot(irr_lasthours, aes(Timestamp, Value)) +
    geom_line() + xlab("") + ylab("irradiance (W/m2)")

  1. historical data from July till August 2014, using from and to on month level
irr_2014 <- get_timeseries_tsid("78930042", 
                                from = "2014-07-01", 
                                to = "2014-08-01")
ggplot(irr_2014, aes(Timestamp, Value)) +
    geom_line() + xlab("") + ylab("irradiance (W/m2)")

  1. historical data for one day from July 1st 2014, using from and period 
irr_2014day <- get_timeseries_tsid("78930042", 
                                from = "2014-07-01", 
                                period = "P1D")
ggplot(irr_2014day, aes(Timestamp, Value)) +
    geom_line() + xlab("") + ylab("irradiance (W/m2)")