This page is English Version of the Japanese article of this blog.
WMS has weak points as pointed out in the article before. SVG Map can offer a complementary solution. Then, a concrete adjustment point of the specification of SVG Map and WMS is described as follows.
Cross-reference of specification:
- In the specification of WMS, SVG is provided for as one of the format of map drawing.
- In the specification of SVG Map, the GetMap request of WMS can be treated as one of the enhanced query part of URL.
Therefore, they have adjusted mutually.
Geographic coordinates of map:
- SVG Map buries geographic coordinates as metadata in map data.
- Geographic coordinates for the map appear on query part of the protocol in WMS.
Therefore, it is necessary to memorize the requested parameter in WMS to maintain geographic coordinates for the downloaded map. SVG Map will solve this problem.
Tiled map:
- SVG Map supports tiling by preparing container SVG data. Container SVG data refers to the tile data by URL.
- WMS can generate the tile of the arbitrary division. The tile can be accessed by enhanced URL (GetMap request).
SVG Map client doesn't know the access method to the map server excluding URL of tile data described in container SVG data. That is, the accesses other than these URL do not occur. Then, the server of WMS can achieve speed-up by caching URL described in container SVG data.
Layering:
- SVG Map supports layering by preparing container SVG data. Container SVG data refers to each layers by URL. (That is the Hyper-Layering.)
- WMS can generate the arbitrary layer. The layer can be accessed by enhanced URL.
On the other hand, the support of layering function on the server side is a difficult in the point of the performance.
Therefore, the WMS protocol and SVG Map adjust well, and will be able to have a supplementary relation.
Special purpose XML languages for WMS:
On the other hand, SVG Map doesn't basically support data other than the SVG format. (However, PNG and JPEG are supported. ) That is, the interpretation of data by proper XML languages for WMS (response data of GetCapability and GetFeatureInfo request) is outside the specification of SVG Map.
However, a considerable functions that those languages aims will be able to be converted into container SVG of SVG Map. This conversion will be able to be achieved by processing by javascript on the client side, or batch processing at data origination, or dynamic processing on server side etc. Convertible functions are as follows.
- Notification of range of map that server offers
SVG Map client doesn't know the access method to the map server excluding URL of tile data deployed in container SVG data. That is, the range of the map service can be transmitted to the client by deploying as URLs of container SVG. - Notification of kind of layers that server offers
SVG Map client doesn't know the access method to the map server excluding URL of tile data deployed in container SVG data. That is, the kind of the layers that provides the map service can be transmitted to the client by deploying as container SVG.
GetMap Protocol:
On the other hand, there might be a lots of use cases that tells the server the value of a geographic view box of the viewer for the SVG Map platform. Therefore, sharing the means for it might be significant. And, it is appropriate to use query part of http GET as this means. The GetMap request of WMS will be able to be used as the concrete specification. We plan to establish this function as one of the specifications of SVG Map Profile.
