How do we add a truly custom provider (like NASA's M20 Mars feed)?

[olyerickson]

NASA is maintaining an excellent tiles API for the Jezero Crater area, "home" to the Perseverance Rover and the Ingenuity helicopter drone:

https://mars.nasa.gov/mmgis-maps/M20/Layers/M20_HiRISE_RGB_mosaic_25cm_v4p2/{z}/{x}/{y}.png

(valid zoom levels are 11:19)

Unfortunately, there doesn't seem to be any easy way to simply add this to the providers brought in by leaflet.providers. What is the best way to "point" Leaflet at such a "custom" endpoint??

NOTE: I've made an attempt, by "forking" the leaflet.providers package and adding a "M20" provider using the above, but it only "sort-of" works. I can observe when forced invalid requests for tiles are made by Leaflet (ie "good errors"), but I'm not actually seeing tiles when valid requests are made (no errors are seen in e.g. Chrome console). I know that Leaflet is doing the slippy math correctly.

Advice is welcome!!

[olyerickson]

These are the valid tiles for NASA's M20 endpoint (ie the Jezero Crater area):

x_min  y_min  x_max  y_max y_dim x_dim total_tiles zoom
1   1463   1130   1465   1131     2     3           6   11
2   2927   2260   2930   2262     3     4          12   12
3   5855   4520   5860   4525     6     6          36   13
4  11710   9041  11720   9050    10    11         110   14
5  23421  18083  23440  18101    19    20         380   15
6  46843  36167  46880  36202    36    38        1368   16
7  93687  72334  93760  72404    71    74        5254   17
8 187375 144669 187521 144809   141   147       20727   18
9 374751 289338 375043 289618   281   293       82333   19

[olyerickson]

I've also tried simply adding the provider via addTiles(), e.g.:

leaflet(
  options =
    leafletOptions(
    #   crs = leafletCRS(
    #     crsClass = "L.Proj.CRS",
    #     code = "EPSG:3006",
    #     proj4def = "+proj=utm +zone=33 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs",
    #     resolutions = c(
    #       256),
    #     origin = c(0, 0)
    #   )
    # )) %>%
      crs = leafletCRS(crsClass = "L.CRS.EPSG3857"))) %>%
  addTiles(
    urlTemplate = "https://mars.nasa.gov/mmgis-maps/M20/Layers/M20_HiRISE_RGB_mosaic_25cm_v4p2/{zoom}/{x}/{y}.png",
    attribution = "Mars via NASA",
    options = tileOptions(minZoom = 11, maxZoom = 19)) %>%
  setView(-18.44222, 77.42151, 12)

[olyerickson]

I'm convinced this is e.g. a Leaflet option or config issue and not a provider issue; it's clear Leaflet is accepting the M20 provider URL via addTiles(). The problem is Leaflet not rendering the png's being returned.

[olyerickson]

I discovered that by adding the M20 placenames layer, things suddenly work (but Leaflet reverses the rows):

library(leaflet)

points <-     cbind(y=rnorm(40)/30 + 77.42151, x=rnorm(40)/30 + -18.44222)

leaflet(
  options =
    leafletOptions(
      crs = leafletCRS(crsClass = "L.CRS.EPSG3857",
                       resolutions = c(256),
                       bounds = c(-18.53349066,
                                  -18.35094107,
                                  77.32109070,
                                  77.52193451))
    )) %>%
  addTiles(
    # Surface tiles
    urlTemplate = "https://mars.nasa.gov/mmgis-maps/M20/Layers/M20_HiRISE_RGB_mosaic_25cm_v4p2/{z}/{x}/{y}.png",
    attribution = "Mars via <a href=\"https://mars.nasa.gov\">NASA</a>",
    options = tileOptions(minZoom = 11,
                          maxZoom = 19,
                          tms = FALSE)) %>%
  addTiles(
    # Place names tiles
    urlTemplate = "https://mars.nasa.gov/mmgis-maps/M20/Layers/M20_Placenames_175k_800dpi/{z}/{x}/{y}.png",
    attribution = "Mars via <a href=\"https://mars.nasa.gov\">NASA</a>",
    options = tileOptions(minZoom = 11,
                          maxZoom = 19,
                          tms = FALSE)) %>%
  setView(77.42151, -18.44222, zoom = 12) %>%
  addMarkers(data = points)

[mdsumner]

can you point to a valid tile in particular?

I don't see anything at https://mars.nasa.gov/mmgis-maps/M20/Layers/M20_HiRISE_RGB_mosaic_25cm_v4p2/11/0/0.png (or any others that I can determine)

in general these are easy to hit up with GDAL readers (which wouldn't help leaflet, but at least I thought I could validate what you should see), but (while you say it works in part) I can't see anything so I'm wondering how to hone in

[mdsumner]

ah, no worries I got one using your table of tile index above, thanks! I'll come back if I figure anything helpful (having trouble with the WMTS services because of the non-earth projection, but I should be able to get around that) - I wonder if there's a radius-assumption in leaflet configs because of the pixels-per-degree being different from the 20037508 earth extent?

oh here's the one I hit up: https://mars.nasa.gov/mmgis-maps/M20/Layers/M20_HiRISE_RGB_mosaic_25cm_v4p2/11/1463/1130.png

[olyerickson]

Please close this ticket. After further research (and interaction with NASA!!) , we've established how to make the NASA M20 endpoint work as TMS. Here is a minimal example: NOTE: Please update the Leaflet et.al. documentation to make it clear that BOTH `{-y}` AND `tms=TRUE` are required!!!! ``` library(leaflet) # Random test points in the Jezero area points <- cbind(y = rnorm(40) / 100 + 77.42151, x = rnorm(40) / 100 + 18.44222) leaflet() %>% addTiles( # Surface tiles urlTemplate = 'https://mars.nasa.gov/mmgis-maps/M20/Layers/M20_HiRISE_RGB_mosaic_25cm_v4p2/{z}/{x}/{-y}.png', attribution = "Mars via <a href=\"https://mars.nasa.gov\">NASA</a>", options = tileOptions( minZoom = 11, maxZoom = 19, tms = TRUE ) ) %>% addTiles( # Place names tiles urlTemplate = "https://mars.nasa.gov/mmgis-maps/M20/Layers/M20_Placenames_175k_800dpi/{z}/{x}/{-y}.png", attribution = "Mars via <a href=\"https://mars.nasa.gov\">NASA</a>", options = tileOptions( minZoom = 11, maxZoom = 19, tms = TRUE ) ) %>% setView(lng = 77.42151, lat = 18.44222, zoom = 15) %>% addMarkers(data = points) ```