Vishful thinking…

GIS Standards gone crazy (EPSG especially)

Posted in GIS by viswaug on April 1, 2009

A couple of weeks ago I had written about how the different axis ordering that can be defined in EPSG coordinate system standards makes the lives of any GIS software provider that wants to implement these standards a whole lot harder. Today, I came across some information that really doesn’t make any sense to me. Previously Morten had written about EPSG finally getting around to adding the web mercator to their standards with the EPSG code “3785”. But in February, EPSG decided to change the EPSG code from “3785” to “3857”. Look at the change request info in the image below. That information can be obtained at



Also, as you might have already heard, OGC had accepted KML as an OGC standard sometime last year. The KML standard includes its own method of defining styles/symbology for 2D & 3D features along with other things. But OGC in fact already had its own existing standards for defining 2D feature styles/symbology in map layers called the Styled Layer Descriptor (SLD).

Now, the OGC has two standards to define features styles in XML which really kind of makes it a double standard.

Now, from what I read, the OGC is working on combining both those standards into one. Which is going to be a tough job since there are so many overlaps between KML and other existing OGC standards.


Lack of good transparency support in Silverlight and what it means to online mapping apps

Posted in ESRI, GIS, Silverlight by viswaug on April 1, 2009

The support for transparency in PNG images in Silverlight is to say the least really bad. Here is what the Microsoft docs says about PNG transparency support in Silverlight

Silverlight does not support all possible color depths that are included in the PNG specification. The following are the PNG color depths supported in Silverlight:

  • Indexed color: 1-bit, 4-bit, or 8-bit color depth (per channel).
  • Truecolor: 24-bit color depth, or 32-bit color depth (per channel) for truecolor plus alpha.

Notably, gray scale (with or without alpha), and 64-bit truecolor, are not supported in Silverlight.

Note that they don’t mention anything about the support for 1, 2, 4 and 8 bit PNGs. This creates some problems when using the ESRI Silverlight API and you might what to keep your eye out for it and pay good attention to how your map caches are being generated. Look at the results when I overlay ArcGIS Online’s Transportation layer on top of the Imagery layer in the ESRI Silverlight maps.

<esri:Map x:Name=“MyMap” Grid.Row=“1” Grid.Column=“2”>










And here it what the map look like. As you can see, the the tile areas outside the continental US are grayed out.


Also, check out this Silverlight forum post where Morten schools Microsoft about the issue mentioned above.