The students in one of our labs have been cranking out daily satellite derived Sea Surface Temperature and Chlorophyll maps for a few years. They are published for public consumption and we have been using them in our global visualization lab overlaid on Google Earth for years.
We have been making them available on a lab website in the browser overlaid on Google Maps and as a Google Earth plugin. Now we would like to embed them into an ArcGIS Online web app so they can be more easily embedded on other lab pages.
The problem is that ArcGIS Online appears to be shifting the PNG overlay images, but a colleague of mine who has ArcGIS Desktop says that the images are not shifted when he opens the KML files using them using Desktop.
We opened a ticket with ESRI support and the answer we got back was:
"The reason for this discrepancy comes from the difference in projections between Google Earth and ArcGIS Online. Google Earth uses a "Simple Cylindrical projection with a WGS84 datum for its imagery base" [see reference: https://support.google.com/earth/answer/148110?hl=en] while ArcGIS Online uses WGS 1984 Web Mercator (Auxiliary Sphere). While these projections are similar, they're not the same, and therefore you will not see the exact same results in both maps when displaying the same data." And that "Although you are correct in that the data does not align in AGOL identical to Google Earth, the data is still be displayed as-expected, so I won't be able to log a bug or enhancement request for this situation."
While I imagine we could try to alter our code so that the PNG file is based on a different projection, I'm thinking that will hose those users who are referencing them for their research as now they'll have a problem displaying the KMLs using Google Earth. Plus I'm confused why ArcGIS Desktop would display them properly and ArcGIS Online would shift them.
The PNG files that the KMLs reference are updated daily and are available here: http://modata.ceoe.udel.edu/dev/mcimino/MODIS/GSFC/KMZ/ and http://modata.ceoe.udel.edu/dev/dhaulsee/MODIS/GSFC/KMZ/
Any thoughts as to how we can resolve this so that the existing users of the data aren't disrupted but where ArcGIS Online web apps can be leveraged to facilitate expanded web visualizations of the data? It seems naive if ArcGIS Online claims to display KMLs, but only if they're re-projected specifically for use on ArcGIS Online only.