We have been working to continue the evolution and compliance with the Web Map Tile Service (WMTS) specification. The following email outlines two areas in which we have modified our WMTS compliance. For additional information, please refer to the GIBS documentation located at http://earthdata.nasa.gov/gibs.
Time Dimension
Unique to the GIBS implementation of the WMTS specification is the underlying data's dependence upon date. GIBS imagery provides a full global image for every day, unlike static maps like Bing or Google Maps. Previously, the GIBS WMTS endpoint utilized an additional, unspecified, parameter for time. Our WMTS GetCapabilities responses now include a formal time dimension within each layer's definition. A sample Dimension block is shown here:
<Dimension> <ows:Identifier>time</ows:Identifier> <UOM>ISO8601</UOM> <Default>2013-05-29</Default> <Current>true</Current> <Value>2012-05-08/2013-05-29/P1D</Value> </Dimension>
(Note: "2012-05-08" and “2013-05-29” will be replaced by the layer's start and end UTC date, respecitvely)
The parts of the Dimension data structure are taken from the WMTS 1.0.0 spec (Table 9, p. 22). However, since the WMTS spec doesn't address the time dimension (other than the use of "Current"), we are adapting some aspects of the WMS spec regarding the time dimension, specifically:
- The contents of the <UOM> part match the contents of the "units=" attribute in the WMS <Dimension> element.
- The contents of the <Value> part match the contents of the WMS <Extent> element.
If the time dimension is omitted in the WMTS request, tiles for the current UTC date will be returned. Be aware that many of the current date’s tiles will be empty because the imagery is generated as the satellites orbit from east to west.
We are working with the OGC WMS SWG to continue to growth of the WMTS standard and specifically to deal with limitations like this that we run into.
RESTful Access
In addition, our WMTS now supports RESTful requests as specified in the GetCapabilities document:
The template is of the form:
and a sample request is:
If you have any questions, please contact support@earthdata.nasa.gov
