transformation between WGS 84 Web Mercator / WGS84 Web Mercator (Auxiliary Sphere) and WGS 84 (ellipsoid)

23191
2
05-17-2015 12:26 AM
Labels (1)
larryzhang
Occasional Contributor III

Team,

You may already read the articles on WGS 84 Web Mercator / WGS84 Web Mercator (Auxiliary Sphere) and WGS 84 (ellipsoid). For example,

  1. The Google Maps / Bing Maps Spherical Mercator Projection | Alastair Aitchison
  2. http://blogs.esri.com/esri/arcgis/2010/03/05/measuring-distances-and-areas-when-your-map-uses-the-me...

In practice, how do you deal with the datum/projection transformation between WGS 84 Web Mercator / WGS84 Web Sphere Mercator  and WGS 84 (ellipsoid). Also, how to transfer major local datum /projection like WKID 102204 (Ain_el_Abd_1970_Aramco_Lambert_2 ) into WGS 84 Web Mercator / WGS84 Web Sphere Mercator  'properly'?

Any advice?

0 Kudos
2 Replies
MelitaKennedy
Esri Notable Contributor

If you're using EPSG:3857 / ESRI: 102100 / OpenLayers:900913, you don't need to do anything different than converting to the regular old EPSG:4326, WGS 1984. The funky WGS 1984 "sphere" conversion is done in the projection algorithm, rather than via a geographic/datum transformation. You would just need to pick or define a transformation to convert from Ain el Abd 1970 to WGS 1984.

If you're using Esri:102113 or EPSG:3785 (why??), those do use a sphere-based GeoCRS and you had to do some sort of bookkeeping transformation to convert between then. However, no actual coordinate change takes place.

Melita

larryzhang
Occasional Contributor III

Thx, Melita,

...

The funky WGS 1984 "sphere" conversion is done in the projection algorithm, rather than via a geographic/datum transformation.

...

It looks that some offsets exist, in the North part of the Middle East Peninsula, if no transformation applied.

Your info gives some hints, which may trigger me to try something else.

+++++++++++++

For EPSG 3785, one of the reasons that our customers accept 'was' as follows:

EPSG:3785

Popular Visualisation CRS / Mercator

  • WGS84 Bounds: -180.0000, -85.0000, 180.0000, 85.0000         
  • Projected Bounds: -20037508.3428, -19971868.8804, 20037508.3428, 19971868.8804
  • Scope: Certain Web mapping and visualisation applications.
  • Last Revised: March 14, 2008
  • Area: World - 85°S to 85°N
0 Kudos