[FEATURE] add built in coordinate conversions

Hello,

The GIS and mapping capability of Bokeh is good and growing but lacks ability to convert units between (lat,lon) pairs and Web Mercator Easting and Northing coordinate pairs.

pyproj is a simple, focused and mature coordinate conversion utility for converting between recognized standard coordinate frames.

Adding pyproj or a similar capability would allow native Bokeh code and examples to perform coordinate conversions as a normal part of GIS mapping and plotting. For example, this code and associated documentation example could be included:

I propose adding pyproj. How can this get considered for the next version update?

Alternative codes and methods:

1. OpenStreetMap Mercator wiki with conversions written in multiple programming languages
2. Web Mercator projection wiki has formulas and good explanations

References:

1. discourse link located here.
2. pull request with working example except for pyproj dependency.

[jbednar]

For what it’s worth, Datashader also needed the specific projection from lon,lat to web Mercator for our examples, and to avoid having a dependency on pyproj we just added that specific function in a numpy/pandas compatible form:

import numpy as np 
def lnglat_to_meters(longitude, latitude):
    """
    Projects the given (longitude, latitude) values into Web Mercator
    coordinates (meters East of Greenwich and meters North of the Equator).

    Longitude and latitude can be provided as scalars, Pandas columns,
    or Numpy arrays, and will be returned in the same form.  Lists
    or tuples will be converted to Numpy arrays.

    Examples:
       easting, northing = lnglat_to_meters(-40.71,74)

       easting, northing = lnglat_to_meters(np.array([-74]),np.array([40.71]))

       df=pandas.DataFrame(dict(longitude=np.array([-74]),latitude=np.array([40.71])))
       df.loc[:, 'longitude'], df.loc[:, 'latitude'] = lnglat_to_meters(df.longitude,df.latitude)
    """
    if isinstance(longitude, (list, tuple)):
        longitude = np.array(longitude)
    if isinstance(latitude, (list, tuple)):
        latitude = np.array(latitude)

    origin_shift = np.pi * 6378137
    easting = longitude * origin_shift / 180.0
    northing = np.log(np.tan((90 + latitude) * np.pi / 360.0)) * origin_shift / np.pi
    return (easting, northing)

[comperem]

@bryevdv ,

Did the simple GIS coordinate conversion submitted by @jbednar [immediately above] (https://github.com/bokeh/bokeh/issues/10009#issuecomment-636555037) ever get added?

It looks like this task was dropped, or never initiated. If I recall correctly, this unit conversion code was the only remaining detail needed to get the mapping tile demo integrated into the Bokeh code base.

What’s the next step to completion?

This thread is already a feature request. How about putting that function in a new file in a new folder called GIS_utils or something similar?

Nobody knows how to proceed except seasoned maintainers.

Marc