R Workshop

Before We Begin

• The EPSG code for ITM is 2157 ( see https://epsg.io/2157 )

• A useful online tool is https://irish.gridreferencefinder.com/

• We will use the {sf} R package

library(sf)

Worked Example 1: The Spire

• The ITM co-ordinate for the Spire of Dublin on O’Connell Street is \((715830, 734697)\).

• The corresponding WGS84 coordinates are \((53.349799, -6.260265)\). (N.B. Google Maps reports a coordinate on a Latitude, Longitude basis)

GPO_ITM <- c(715830, 734697)

GPO_GPS <- GPO_ITM  %>%
  st_point() %>%
  st_sfc(crs = 2157) %>%
  st_transform(4326)

GPO_GPS

## Geometry set for 1 feature 
## Geometry type: POINT
## Dimension:     XY
## Bounding box:  xmin: -6.260248 ymin: 53.34979 xmax: -6.260248 ymax: 53.34979
## Geodetic CRS:  WGS 84

## POINT (-6.260248 53.34979)

• Note that {sf} and R report the coordinate on a Longitude-Latitude basis

Worked Example 2: The Cork Opera House

• The WGS 84 co-ordinate for the Cork Opera House is \((51.9002522,-8.4752863)\).

• The corresponding ITM coordinates are \((567469,572117)\).

COH_GPS <- c(51.9002522,-8.4752863)

COH_ITM <- COH_GPS  %>%
  rev() %>%
  st_point() %>%
  st_sfc(crs = 4326) %>%
  st_transform(2157)

COH_ITM

## Geometry set for 1 feature 
## Geometry type: POINT
## Dimension:     XY
## Bounding box:  xmin: 567291.8 ymin: 572117.9 xmax: 567291.8 ymax: 572117.9
## Projected CRS: IRENET95 / Irish Transverse Mercator

## POINT (567291.8 572117.9)

Worked Example 3: Increasing the Accuracy

COH_GPS <- c(51.90025879194425, -8.472700675148365)

COH_ITM <- COH_GPS  %>%
  rev() %>%
  st_point() %>%
  st_sfc(crs = 4326) %>%
  st_transform(2157)

COH_ITM

## Geometry set for 1 feature 
## Geometry type: POINT
## Dimension:     XY
## Bounding box:  xmin: 567469.7 ymin: 572117.5 xmax: 567469.7 ymax: 572117.5
## Projected CRS: IRENET95 / Irish Transverse Mercator

## POINT (567469.7 572117.5)