Copyright © 2012 Open Geospatial Consortium
80 A path has multiple key areas of interest bounding boxes where each AOI bounding box is a set
of four points. As we move forward or backward in time, the server is interpolating each point between consecutive key AOIs using a pre-defined interpolation method. The result is an
intermediate AOI at a given instant in time between the two key AOIs. From a server’s perspective, an intermediate frame is one GetMap request asking for one AOI.
Figure 12: Example path based AOI rendering of WAMI data
23.4 GetMap in WMS and Image Service
As you can see, a GetMap request in an Image Service IS is almost identical to a GetMap request in OGC WMS. There are a few differences but they are fundamental.
1. In Image Service, the CID parameter replaces the Layers parameter. The server
implementation may choose to implement the fact that the system only handles one collection per request CID=a or multiple collections in a single request specified as a
comma separated ordered list of Collection IDs CID=a,b,c.
2. The Time parameter implementation is required in IS but it is optional in WMS. It shall have
the idea of specifying time value and time ranges as set by OGC as well as in terms of absolute frame numbers. Both methods are intuitive, provided some preliminary information
is available from a Collection Service metadata response for leaf nodes from a collection tree. If the server implements multiple frame requests, it must support a response that enables
having multiple separate data elements in a single response message. For instance: a. If absolute frame numbers of collections are known, then requesting for frame numbers
becomes more intuitive than time ranges based on time of acquisition.
Time = T1 + 10s Time = T1 + 8s
Time = T1 + 3s Time = T1
Example: Original WAMI data has 20 frames captured at 2 FPS, at times T1, T1+0.5s, T1+1s,
T1+1.5s… until T1+19.5s. Rendering uses Catmull‐Rom spline interpolation
6 map images Smooth movement
Feels like zooming out while panning
10 map images Smooth movement
Feels like zooming in while panning
4 map images Smooth movement
Feels like a fast pan 1280
7 2
20, 1280 x 720 map images rendered using four key AOIs
Copyright © 2012 Open Geospatial Consortium
81 b. If the time of acquisition of each frame is known and reasonably constant, even if the
request asks for a frame at an approximate time of acquisition or frame within a temporal range for an given bounding box AOI for a set of collections.
c. The specification could resolve any ambiguity in dereferencing a time value into an absolute frame number within a collection. For example, the specification may state: If
for a given collection, the requested time of acquisition T matches frame F
A
at time of acquisition T
A
and F
B
at time of acquisition T
B
because |T-T
A
| = |T-T
B
| then select F
A
, if F
A
F
B
. d. While this determination is completely arbitrary, it removes any ambiguity.
e. It could be made more complex by selecting F
A
or F
B
based on the context of the value of T. That is, for time ranges, select F
A
, if F
A
F
B
for start time of acquisition ambiguity resolution, and select F
B
, if F
A
F
B
for end time of acquisition ambiguity resolution. f. It is however recommended that time of acquisition to frame number ambiguity
resolution should be kept as simple as possible.
3.
A parameter named Metadata is introduced to include metadata in the response as part of a multipartRelated response content-type. The Disposition needs to be one of ‘ordered’ or
‘unordered’ for Metadata to be returned as part of a GetMap multipart request. It is generally useful for high latency environments. The implementation of this parameter is optional. The
Metadata parameter, if supported, shall be constrained to the allowed values of the GetCapabilities response.
24 IS service model
24.1 Summary
