Error in png::readPNG(img) : file is not in PNG format

[gremms1]

Hello,

I am trying to get the following code to work, but it's not working out:

library(sf)
library(maptiles)

p = st_point(c(110784.2,494605.3))
p = st_sfc(p)
p = st_set_crs(p, 28992)
bb = st_bbox(st_buffer(p, 300))

url <- "https://geodata.nationaalgeoregister.nl/tiles/service/wmts/opentopo/EPSG:28992/{z}/{x}/{y}.png"
mffp <- list(src="OpenTopo", q=url, sub=NA, cit='')

t <- get_tiles(bb, provider=mffp, crop= T, forceDownload = T, zoom=5)

I get the following error: Error in png::readPNG(img) : file is not in PNG format
The strange this is that entering the following url in my browser does yield the correct tile:
https://geodata.nationaalgeoregister.nl/tiles/service/wmts/opentopo/EPSG:28992/5/16/12.png
So the error that it throws me seems strange.

[rCarto]

Hello,
I've tried to save this tile (right-click, save):
https://geodata.nationaalgeoregister.nl/tiles/service/wmts/opentopo/EPSG:28992/5/16/12.png
and saw that the file is actually a jpeg despite its png extension.

So I tried this url for the tile server:

url <- "https://geodata.nationaalgeoregister.nl/tiles/service/wmts/opentopo/EPSG:28992/{z}/{x}/{y}.jpeg"

but maptiles does not understand jpeg extension, only jpg and png.
So I've update maptiles to allow jpeg extension and you can try this (using the dev version of the package):

remotes::install_github('riatelab/maptiles')

library(sf)
#> Linking to GEOS 3.9.0, GDAL 3.2.2, PROJ 7.1.0; sf_use_s2() is TRUE
library(maptiles)

p = st_point(c(328452.9,267552.5))
p = st_sfc(p)
p = st_set_crs(p, 28992)
bb = st_bbox(st_buffer(p, 300000))

url <- "https://geodata.nationaalgeoregister.nl/tiles/service/wmts/opentopo/EPSG:28992/{z}/{x}/{y}.jpeg"
mffp <- list(src="OpenTopo", q=url, sub=NA, cit='')

t <- get_tiles(bb, provider=mffp, crop= T, forceDownload = T, zoom=7)
plot_tiles(t, adjust = TRUE)

^{Created on 2022-02-15 by the reprex package (v2.0.1)}

I have modified point coordinates and zoom level from your original example to show something not on the sea :-)

[gremms1]

Hi, I came to the same conclusion (concerning the jpeg) yesterday evening! Thanks for acting so promptly. Getting the tiles now works, the only thing I can´t figure out is what is going wrong with the projection. Using the following code

library(sf)
library(maptiles)
library(stars)
library(tmap)
p = st_point(c(328452.9,267552.5))
p = st_sfc(p)
p = st_set_crs(p, 28992)
bb = st_bbox(st_buffer(p, 300000))
url <- "https://geodata.nationaalgeoregister.nl/tiles/service/wmts/opentopo/EPSG:28992/{z}/{x}/{y}.jpeg"
mffp <- list(src="OpenTopo", q=url, sub=NA, cit='')
t <- get_tiles(bb, provider=mffp, crop= T, forceDownload = T, zoom=7)
plot_tiles(t, adjust = TRUE)
map <- stars::st_as_stars(t)
tmap_mode("plot")
tm_shape(map) +
  tm_rgb() +
tm_graticules(lines=F)

shows that the map is way bigger than it actually should be.

[rCarto]

I suspected something odd with the projection stuff.
I think it has something to do with this part of the url (and the way tiles are delivered): EPSG:28992
Most of tiles providers ask for lon & lat in EPSG:4326 and offer tiles in EPSG:3857 (web mercator) and this projs are actually hardcoded in maptiles.
Can you direct me to the API documentation just to be sure of what input/output proj are expected?

[gremms1]

I think you're right. this is the KVP WMTS GetCapabilities page. If you ctrl+f and search for opentopo you can see EPSG:28992. Thanks for your help!

[gremms1]

Additionally, here a working example with an interactive tmap (requires dev-version):

remotes::install_github('r-tmap/tmap')
library(tmap)
library(leaflet)
epsg28992 <- leafletCRS(
  crsClass = "L.Proj.CRS"
  ,code = "EPSG:28992"
  ,proj4def = "+proj=sterea +lat_0=52.15616055555555 +lon_0=5.38763888888889 +k=0.9999079 +x_0=155000 +y_0=463000 +ellps=bessel +towgs84=565.417,50.3319,465.552,-0.398957,0.343988,-1.8774,4.0725 +units=m +no_defs"
  ,origin=c(-285401.92,903401.92)
  ,resolutions = c(3251.206502413005,1625.6032512065026,812.8016256032513,406.40081280162565,203.20040640081282,101.60020320040641, 50.800101600203206,25.400050800101603,12.700025400050801,6.350012700025401,3.1750063500127004,1.5875031750063502,0.7937515875031751,0.39687579375158755,0.19843789687579377,0.09921894843789689,0.04960947421894844)
)

url <- "https://geodata.nationaalgeoregister.nl/tiles/service/wmts/opentopo/EPSG:28992/{z}/{x}/{y}.jpeg"


data(World)
tmap_mode("view")

tm_shape(World) +
  tm_polygons() +
  tm_basemap(NULL) +
  tm_view(projection = epsg28992, set.view = c(5.092098,52.093992,4)) +
  tm_tiles(server = url) +
  tm_mouse_coordinates()