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neilcharles / geoviz

Functions to make it easy to process DEM data and add GPS traces to rstats Rayshader scenes, and to overlay mapbox and elevation shading imagery
http://www.hilltop-analytics.com
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Having trouble with OS Terrain 50 #40

Closed BeetrootShoulders closed 4 years ago

BeetrootShoulders commented 4 years ago

Having trouble using this with OS Terrain 50. I get the following error:

Error in mosaic_files("terr50_gagg_gb/data/nn", extract_zip = TRUE, zip_file_match = ".*GRID.*.zip", : Input files have no CRS, use the file_crs option to set it

neilcharles commented 4 years ago

You need to tell it the CRS of the OS Terrain 50 files. Try adding this to your mosaic_files() call.

file_crs = 'EPSG:27700'

I'm away from my personal machine so let me know if that fails & I'll test it properly.

BeetrootShoulders commented 4 years ago

That threw an error so I did a bit of Googling and found that it in fact needs:

file_crs = '+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +datum=OSGB36 +units=m +no_defs '

However, on running I now get a fresh error:

Unzipping files...
Merging files...
Error in .local(.Object, ...) : 

Error in .rasterObjectFromFile(x, band = band, objecttype = "RasterLayer",  : 
  Cannot create a RasterLayer object from this file.
neilcharles commented 4 years ago

This should be fixed now, thanks for logging the issue.

Use this snippet to run the merge (also changed in the readme), which changes file_match so that it doesn't pick up an extra xml file from the OS Terrain 50 zip files. I've also fixed a bug in the merge function.

mosaic_files(
  "path/to/zip/files",
  extract_zip = TRUE,
  zip_file_match = ".*GRID.*.zip",
  file_match = ".*.asc$",
  raster_output_file = "mosaic_out.raster",
  file_crs = '+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +datum=OSGB36 +units=m +no_defs'
)

Until it's on CRAN, install with remotes::install_github("neilcharles/geoviz")