Level Of Detail(2)

Satoru Takagi W3C SVGWG

6.21.2016

Update on standardization (6.21.2016)

Difficulty

• At webperf WG, the spec. investigation for deferred loading and lazy loading freezes.*1

• Difficulties in proposal work for putting into Media query at zoom feature *2

Progressed

• The work for defining the detailed concept of zoom at css sets up*3 , *4 in response to a zoom feature proposal.

• Investigation of the relation between complicated but practical Level od Detail logic and the contents of standardization (See the following pages)

Complicated but practical Level of Detail logic

• Microsoft’s Zoomable High-Res. Photoshttp://www.microsoft.com/web/solutions/zoomit.aspx

• Many Maps: google maps, openstreetmap etc.• And my implementations (Vector Map based on SVG)

http://svg2.mbsrv.net/devinfo/devkddi/lvl0.1/airPort_r11.html

Incidentally, such a processing explained on the following pages is already implemented on all the examples shown last time.

Determine the resource set which should be used based on zoom scale

1 < zoom <= 2

2 < zoom

largeImageTiles.svgmidImageTiles.svg

Level Selection step

Chiefly, it is about processing at the Level Selection step based on zooming. (see part one slide)

Zoom-in (Zoom=2.0) Loading(Zoom=2.0) Load completed (Zoom=2.0)

ResourcesFor zoom <= 1

Without such processing

With such processing

Initial state (Zoom=1.0)

Expands and displays loaded resources in spite of out of zoom range for a while.

Overwrite progressively.Remove tentative out of range resources.

Rendering is impossible for applicable resources have not been loaded yet.

Complicated but practical Level of Detail logic 2It is about processing for improving UX during transition until resource fetching for the applicable level is completed

What loading completed can be displayed progressively.

Resorcesfor 1 < zoom <= 2

Required functionality

The function to just change display status of the element for each zoom ranges is insufficient.

1. The data structure which can show an alternative resource in case loading is not completed is required.

2. Of course, it is also required to express and process the conditions that loading is not completed.

3. There may be many levels of detail. Accordingly, there are cases where alternative resources are specified for many each levels.

4. Such resources may be divided into tiles. And those tiles may be huge.

5. There may also be a case where the resources expected to be required in the near future navigation is pre-fetched speculatively.

We should advance gradual extension from the existing standards as much as possible.

Currently, even investigation of the declarative mechanism for deferred loading has not started yet. Therefore, the measure for requirements No. 2 and 5 may fall to javascript applications for the time being.

On the other hand, requirements No. 1 and 3 are related with the data structure of SVG. Where, in order to correspond to requirements No. 4, such a structure should align the tiling structure by SVG.

Then, elementary search results about the data structure for expressing alternative resources is shown in the following page.

Standardization

<picture> element of HTML• It is well known and designed.• Media queries which it uses does not support not only

complicated conditions which were described previously but zoom ratio.

• It is likely to be applicable only to the image element.• In order to apply to tiling, a certain support to the hierarchical

structure is required.

<switch> element of SVG• It is left alone while it had been maintained insufficiently.• It can support even not only various elements in svg name space

but hierarchical structure. • Its conditional factors are far from Level of Detail more than

media query.

Existing elements expressing alternative resources