plotly / plotly/plotly.py

Scattermapbox fill plotting jagged lines

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bug P3
Dominant language
Python
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Description

Issue

I'm plotting filled polygons on a map using Scattermapbox. It successfully plots the corner markers, but doesn't show a straight line between the two points, seen in the first image. When zooming in on the map, it makes even more jagged lines on all the polygons, seen in the second image.

I tried running the code and opening the .html file on both a windows and linux machine, with the same results.

Specifications
  • Windows 10
  • Chrome 92.0.4515.131
  • python 3.8.11
  • plotly 5.1.0

Issue also appears with:

  • Ubuntu 18.0.45
  • Firefox 91.0 / Edge 91.0.864.64
  • python 3.6.9
  • plotly 4.14.3
Code to produce the images
import numpy as np
import plotly.graph_objects as go

corners1 = np.array([[5.5, 13.6, 6.2, -2.1], [27.2, 25.9, -5.1, -3.9]])
corners2 = np.array([[-12.9, -2.0, -17.3, -25.9], [30.9, 27.9, 9.9, 16.2]])
corners3 = np.array([[27.8, 35.2, 32.3, 24.9], [25.0, 24.0, 1.4, 2.5]])

sat_corners = [corners1, corners2, corners3]

fig = go.Figure()
for corners in sat_corners:
    fig.add_trace(go.Scattermapbox(
        fill="toself",
        lat=corners[:][1],
        lon=corners[:][0],
        marker={'size': 5, 'color': 'royalblue'}))

fig.update_layout(
    mapbox={
        'style': "stamen-terrain",
        'center': {'lat': 11.547231, 'lon': -5.885243},
        'zoom': 3.5},
    showlegend=False,
    margin_t=20, margin_r=20, margin_b=20, margin_l=20
)

fig.show()
fig.write_html('test_map.html')
fig.write_image('test_map.png', width=1000, height=1000, engine='kaleido')
Resulting Images

These images are screengrabs from Chrome:

Dog leg is visible in the lower left corner of the center polygon.
reset_axes

Here, jagged lines are visible on all polygons. Lines stay like this as far as you can zoom in.
small_zoom

These images are the .png files with different zoom parameters given in fig.update_layout:

zoom=4:
test_map_zoom4

zoom=3:
test_map_zoom3

zoom=2:
test_map_zoom2

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by running the supplied Scattermapbox example with the listed polygon coordinates and compare the interactive HTML output with the generated PNG at different zoom levels. Investigate the Scattermapbox fill rendering path and verify the result across the reported browser and Plotly versions. Done means polygon edges render as straight lines without the reported jagged artifacts.

Written by the indexing model from the issue text.

Assessment

Tech stack
plotly, python
Domain
data-visualization
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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