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Fix: Handle sf objects with Z/M dimensions in leaflet rendering #962

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Fix: Handle sf objects with Z/M dimensions in leaflet rendering #962

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@Copilot Copilot AI commented Oct 8, 2025 •
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Problem

Leaflet fails to render simple features (sf objects) with Z (elevation) or M (measure) dimensions, throwing obscure errors instead. This affects LINESTRING, POINT, POLYGON, and other geometry types when they contain 3D or 4D coordinate data.

library(leaflet)
library(sf)

# This fails with an obscure error
s1 <- st_linestring(matrix(c(0, 1, 0, 1, 5, 6), ncol = 3))  # Z dimension
leaflet() %>% addPolylines(data = s1)  # Error!

Root Cause

The internal sf_coords() function expects exactly 2D coordinates (lng, lat) but sf objects with:

  • Z dimension have 3 coordinates (X, Y, Z)
  • ZM dimensions have 4 coordinates (X, Y, Z, M)

When sf_coords() tries to assign 2 names to 3+ columns, it fails with an error.

Solution

Following @jcheng5's suggestion, this PR adds sf::st_zm() calls to remove Z and M dimensions at all entry points where sf objects are processed. The st_zm() function:

  • Safely removes Z and M dimensions from geometries
  • Returns 2D geometries (XY only) suitable for mapping
  • Is safe to call on objects that already don't have ZM dimensions

Changes

Added sf::st_zm() calls to 5 methods in R/normalize-sf.R:

  1. sanitize_sf() - handles sf data frames
  2. pointData.sfc_POINT() - handles sfc_POINT collections
  3. pointData.POINT() - handles individual POINT objects
  4. polygonData.sfc() - handles sfc collections (LINESTRING, POLYGON, etc.)
  5. polygonData.sfg() - handles individual geometry objects

This ensures ZM dimensions are removed regardless of how sf objects enter the leaflet system.

Testing

Added comprehensive test coverage for:

  • LINESTRING with Z dimension
  • LINESTRING with ZM dimensions
  • POINT with Z dimension
  • sf data frames with Z dimension
  • sfc collections with Z dimension

All tests verify that geometries with Z/M dimensions are correctly converted to 2D coordinates and render without errors.

Example

After this fix, the following code works correctly:

library(leaflet)
library(sf)

# Create a linestring with Z dimension
s1 <- st_linestring(matrix(c(0, 1, 0, 1, 5, 6), ncol = 3))

# Now renders successfully!
leaflet() %>% addPolylines(data = s1)

Fixes issue where sf objects with Z or ZM dimensions fail to map.

Original prompt

This section details on the original issue you should resolve

<issue_title>Simple features with ZM dimensions fail to map</issue_title>
<issue_description>Leaflet will not render linestrings with Z or ZM dimensions. Instead it gives an obscure error with an obscure traceback. It would be helpful if leaflet removed or ignored the ZM dimensions or at least gave a helpful error message.

library(leaflet)
library(magrittr)
library(sf)
#> Linking to GEOS 3.6.1, GDAL 2.1.3, proj.4 4.9.3

s1 <- rbind(c(0,3,1),c(0,4,1),c(1,5,1),c(2,5,1))
(ls <- st_linestring(s1))
#> LINESTRING Z (0 3 1, 0 4 1, 1 5 1, 2 5 1)

leaflet(ls) %>% addPolylines()
#> Error in if (length(nms) != n || any(nms == "")) stop("'options' must be a fully named list, or have no names (NULL)"): missing value where TRUE/FALSE needed

# Works
leaflet(st_zm(ls)) %>% addPolylines()
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
<comment_new><author>@jcheng5</author><body>
Looks like there's no harm in calling `st_zm()` on a linestring that already doesn't have ZM, should we just do that always? @bhaskarvk @timelyportfolio </body></comment_new>
</comments>
Fixes #482

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@Copilot @jcheng5
Add st_zm() to sanitize_sf to handle ZM dimensions + tests
564b792 
Co-authored-by: jcheng5 <129551+jcheng5@users.noreply.github.com>
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Copilot AI and others added 2 commits October 8, 2025 20:49
@Copilot @jcheng5
Add st_zm() to all sf geometry methods for comprehensive ZM handling
a63347b 
Co-authored-by: jcheng5 <129551+jcheng5@users.noreply.github.com>
@Copilot @jcheng5
Add test for sfc with Z dimension to match issue example
c76efa0 
Co-authored-by: jcheng5 <129551+jcheng5@users.noreply.github.com>
@Copilot Copilot AI changed the title [WIP] Fix rendering issue for linestrings with ZM dimensions Fix: Handle sf objects with Z/M dimensions in leaflet rendering Oct 8, 2025
Copilot finished work on behalf of jcheng5 October 8, 2025 20:54
@Copilot Copilot AI requested a review from jcheng5 October 8, 2025 20:54
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Simple features with ZM dimensions fail to map

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