Copyright © 2012 Open Geospatial Consortium
78 5. Send a single GetMapGetPathMap request and receive a stream of still images and
optionally metadata.
23.3 Path
One path comprises of one or more tracks. One track comprises of two or more key AOIs that fall within one collection’s spatial and temporal bounds. For each track, the server generates
intermediate AOIs based on these key AOIs. Number of intermediate AOIs can be client controlled or server automated. The server renders a path, i.e. one or more tracks, as a sequence
of images of fixed width and height and delivers them as a stream of images. As soon as the first image is available to the server, it is sent, as soon as the second is available, it is sent, and so on
until all images are sent.
Each path requires the following inputs:
1. Width and height: Dimensions of the output images. All output images from a rendered
path shall be of the same size.
2. Output format: The format in which the output shall be rendered. In our case it is a
sequence of map images in a known file format MIME type.
3. CRS: Coordinate reference system of the input bounding boxes of key AOI points as well as
for the output sequence of map images.
4. Options: Vendor supported special options for formatting the output sequence of map
images.
5. Metadata: Optional inclusion of per frame metadata, the server provides a list of types of metadata that it supports. If Metadata is included, the Output format should be set
accordingly.
6.
Tracks: An ordered-list of tracks.
23.3.1 Track
The reason for having at least two Key AOI values is simple. Use GetMap for everything else. Each track consists of the following inputs:
1. Collection ID: Comma separated ordered list of one or more collection IDs of the collections
from which to extract a sequence of frames that follow this track. Spatial and temporal overlap rules apply to a track in the same manner as they do in a GetMap request.
2. Method: The interpolation method to generate an intermediate AOI corner points from a
sequence of Key AOIs. For example, the server may implement linear interpolation, Ease- inEase-out curve based interpolation, B-spline based interpolation, or a Catmull-Rom spline
based interpolation on the bounding box corner points from one instant in time to the next.
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79
3. A list of Key AOI entries: A list of two or more Key AOI entries2 this is analogous to
specifying key frames in key frame animation. For each Key AOI entry, the required elements are:
a. Bounding Box: The bounding box of the AOI BBOX=minx, miny, maxx, maxy. The
bounding box values are set in the coordinate reference system set in CRS.
b. Time of acquisition: The time of acquisition TOA of a specific frame within the
collection. This value is specified as a single time value or frame number Time=ISO8601 Time Value; Time=Fnumber. The specified bounding box must
at least partially intersect the bounds of the WAMI frame at that specific instant in time. If the TOA is set as an ISO8601 time value and the captured frame does not fall exactly
at that that time, the server maps it to the closest valid captured frame.
c. ΔT: The time increment. This value is specified as frames or seconds between this key
AOI and the next key AOI. The last key AOI shall have a ΔT of zero. If a client sets a key AOI ΔT to be zero and this key AOI entry is not the last key AOI entry, it means the
client is requesting the server to determine the number of intermediate AOIs to generate. Δ
T is assumed to be in frames if Time of acquisition is set in frames. ΔT is assumed to be in seconds if Time of acquisition is set as an ISO8601 time value.
d. Server-side automation of intermediate frames is useful for sensors whose acquisition frame rate is not constant. For instance, assume that this collection was acquired at the
rate of about 1.8 frames per second: e. Consider that a request comprises of two key AOIs.
f. First key AOI is at time T1. g. ΔT is set to 0.
h. The next key AOI is at time T1 + 10 seconds. i.
This means a total of 18 frames were captured from T1 to T1 + 10 seconds. j.
The server returns a sequence of 18 maps images for this section of the track.
k.
Options: Additional information required to define each bounding box vertex. This is vendor specific and may be used for supporting description of parameters required for
curve-based rendering of intermediate AOI maps. For instance, a spline curve based interpolation method may need additional “knobs” when treating each bounding box
vertex as a control point.
23.3.2 Rendering a Track
Rendering of frames is based on the Key Frame Animation technique that has been the basis of moving characters since the advent of traditional and computer animation.
2
Key AOI Entry: A Key AOI entry is analogous to a Key Frame in Key Frame Animation.
