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I am new to this site, and in general, to coding for what I would like to do.

I have used this code in the past, and it worked for when I was working with a map of China, but now I would like to use it for a different region of the world, and I am stuck

I have a 3 part question:

1.) I have a map of Papua New Guinea in GIF format that I would like to convert to a raster (easy)

2) Define coordinates of raster file

3) Lay over a map of Papua New Guinea and make sure it matches the raster of Papua New Guinea that I have created.

Step 1 is done, step 2 I believe is fine (please tell me if you see an error), however, there is a bug between step 2 and 3.

I am using R, and here is the code I have written so far

library(raster)
library(maps)
library(magick)
library(rgdal)

setwd( "where I am working from ")

#upload image

Species_id<-1
Species_i <- image_read(paste("Species (", Species_id, ").gif", sep=""))

Species_i_rotated<-image_rotate(Species_i,0)
image_write(Species_i_rotated, path = "Temporary.png", format = "png")

#create raster
Converted<-raster("Temporary.png", band=1)

# cut raster to fit precisely as possible the borders of Papua new guinea

ext<-c(26,445,0, 275) 

Converted.cr<-crop(Converted, ext)

plot(Converted.cr)

#### This is where step 2 starts and the issue may stem from here, however, I have followed this procedure in the past, and it worked just fine
#Define the coordinates of the borders of the rasters using the sr-org projection 7852 - Australia - modified wgs84
# borders defined manually here http://spatialreference.org/ref/sr-org/7852/

xmin(Converted.cr) <- 41368.792496

xmax(Converted.cr) <- 1715419.242596

ymin(Converted.cr) <- 8696732.363608

ymax(Converted.cr) <- 9783651.873356

# This is where my code will NOT work, and I suspect its because I used this when I was working with China, and something needs to be adjusted, Nonetheless, I get an error: 

crs(Converted.cr) <- "+proj=aea +lat_1=15 +lat_2=65 +lat_0=30 +lon_0=95 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_def"

newproj<-"+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs"

Converted.proj <- projectRaster(Converted.cr, crs=newproj)

Error in if (maxy == miny) { : missing value where TRUE/FALSE needed

# Here is the end goal:

plot(Converted.proj)

map(region="Papua New Guinea", add=T)

here is an example of a map I am working with

enter image description here

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  • 1
    If I understand it right, you defined your boundaries by one coordinate system (SR-ORG:7852) but then you assigned a different one to it. I assume crs(Converted.cr) <- "+proj=tmerc +lat_0=0 +lon_0=145 +k=1 +x_0=500000 +y_0=10000000 +ellps=WGS84 +units=m +no_defs" (this is the proj4string from your link) should be more appropriate.
    – Janina
    Jan 5 '18 at 13:06
  • Hello This was the right answer, and exactly what I was trying to do! Thanks a lot for your help. May I ask, where did you come up with the answer? I would like to know because I will be doing this for other countries as well. Thanks again
    – Andy
    Jan 5 '18 at 13:23
  • @Janina please, post your comment as an answer.
    – aldo_tapia
    Jan 5 '18 at 13:44
  • @aldo_tapia yes, I wasn't sure if that would solve everything. But the OP managed to post the answer before me :-) The whole workflow seems a bit shaky to me but I'd have to see the data.
    – Janina
    Jan 5 '18 at 14:16
  • @Andy right there on the link you provided (SR-ORG:7852) there is a list of the coordinate system definitions used by different softwares. If you click on the Proj4 you will get directly the string which is used in R.
    – Janina
    Jan 5 '18 at 14:19
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The answer was written by Janina, and it was how the boundaries of the coordinate system were assigned.

I changed this, and it works great now!

crs(Converted.cr) <- "+proj=tmerc +lat_0=0 +lon_0=145 +k=1 +x_0=500000 +y_0=10000000 +ellps=WGS84 +units=m +no_defs"

This is the proj4string from your link and should be more appropriate

Many thanks for the quick tip :)

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