Dear All,

I have a dataset of lon/lat coordinates with about two thirds in datum AGD66/84 and the other third in datum WGS84. From what I have read I think there is about a 200m different between these datum. I want to change all of the AGD66 coordinates to be correct in WGS84 to fix this difference.

My data looks like:
lon                          lat                           datum
145.1167              -37.83333             AGD66
144.9756              -38.36555             WGS84

So far I have tried 1:
# to choose the pts from the dataset
pts66<-pts[which(pts$datum=='AGD66'),]
# to assign the AGD66 datum
pts66 = SpatialPoints(cbind(pts66$lon,pts66$lat), CRS("+init=epsg:4202"))
# to transform this data to WGS I have tried two different methods
pts66t = spTransform(pts66, CRS("+init=epsg:3033"))
# and
pts66t = spTransform(pts66, CRS("+proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0"))

The first of these transformations, using CRS("+init=epsg:3033"), transforms the results to the following:
lon                          lat
11736428             3368292

While the second, does not result in any transformation:
lon                          lat
145.1167              -37.83333

Why are these two transformations different? I had thought they would do the same thing because I have used "+proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0" to reproject raster files from one CRS to WGS84.
How can I get the points to transform and stay in the same lon/lat format?

I just want to get the points that were taken in AGD66 to be at the right spot on the map when I use them in conjunction with raster files in WGS84. I think there must be some fundamental concept I am misunderstanding when working with this data. Can anyone help me out and/or point me in the right direction. Thank you very much for your time and help in advance.

Kind regards,

Adam Cardilini,
PhD Candidate,
Deakin University,
School of life and environmental sciences,
75 Pigdons Rd, Waurn Ponds,
Victoria, 3126
Mob: 0431 566 340
adamcardilini.wordpress.com<http://adamcardilini.wordpress.com/>


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