A preliminary study of vector transduction in Webgis

1. Background

In the field of GIS, pyramid technology has always been a fundamental technology, and the WMTS specification specifically developed a format for slicing requests. With this technique, the front end can quickly display a map or image at a specified level.

However, since transduction itself is a picture, the elements of the image that appear to be points of interest simply cannot be interacted with at the front end. Therefore, for the display of vector data such as points of interest, the basic principle is to obtain the vector of geographical information (such as Geojson), in front of the drawing (the kernel is an element), then the element can be mouse response and other interactions.

2. Vector Data General presentation method 2.1 vector data on-demand request

As needed, the data returned by the request is drawn to the front-end each time a request is made to the server, such as based on geographic scope, attribute information.

The advantage is that on-demand requests, data returns are limited, and individual requests are more efficient.

The disadvantage is that frequent interaction with the server, while causing great pressure on the server, multiple requests, even some duplicate requests, will increase the front-end interaction time-consuming, reduce the user experience.

2.2 Vector data one request, show on demand

With the front-end technology becoming more and more mature, the computer memory is more and more large, RIA technology on the display of vector data to do more optimization, one of the common way is the vector data one request, on demand display way.

For example, the following examples are developed using leaflet: http://demo.qunee.com/map/LeafLet+MapABC.html

To view back-end requests:

As you can see, all of the vector information is read to the front end when the page is initialized, and then the clustering is presented according to the requirements.

The advantage is: reduce the interaction with the service side, reduce the pressure on the service side, improve the user experience.

The disadvantage is: the first request to return the amount of data is too large, the network time, the server to meet the first request is also a considerable pressure, and the client computer configuration has a certain dependency.

3. A new solution--vector cut Figure 3.1 What is a vector cut

What is vector transduction? To put it bluntly, it is to cut the vector data into a descriptive file in the form of a pyramid, such as organizing it in Geojson format or in a custom format.

This is a piece of vector data cut out after:

The specific contents of the file are organized in Geojson format:

3.2 Cut diagram Tool 3.2.1 Business Diagram Tool

One of the new highlights of ESRI, unveiled at the recent ESRI conference, is that their Arcgispro products support remote sensing data processing and three-dimensional, highly efficient displays, highlighting the support for vector transduction. However, the product is currently a beta version.

Earlier contact with the Suzhou Super-company, the other side of the product can also support the vector cut diagram, and on this basis, the other side also supports image data compression for streaming front-end real-time display.

3.2.2 Open-source cutting diagram software

Currently support Vector transduction open source software, on the Internet is the most respected Tilestache tools, installation of this tool is more energy-intensive, the following are the tools need to rely on other software environment:

To put it simply, the gdal environment needs to be configured, and the Python environment is configured before it can be used. and currently only tested on the Win7 run, on the win8 can not.

3.3 Front-end support vector tile display

At present, support vector tile display front end has Leaflet,openlayers,arcgis js4.0.

3.3.1 Solutions in ArcGIS js4.0

Show example Address: http://basemapsbeta.arcgis.com/preview/app/index.html

Its supported vector tile format is a format that satisfies Mapbox picture storage (https://www.mapbox.com/).

Solutions in 3.3.2leaflet

Show example Address: http://basemapsbeta.arcgis.com/preview/app/index.html

This is supported by vector tiles in the Geojson format.

4. Shortcomings found in the current study

A. The Vector cutter tool can only cut vector layers in the WGS84 coordinate system.

B.leaflet can only load vector tile data that can be converted to the WGS84 coordinate system.

5. Optimized 5.1 front-end supports vector tiles in any coordinate system

Inherit the Canvastilelayer from the existing GIS framework, rewrite the gettile and parse the redraw using the open source PBF parsing library. Get rid of the limitation of leaflet on vector tile coordinate system. Using this method, vector tiles can be supported in any coordinate system.

5.2 Front-End cache optimization

The read vector tiles are cached to memory in a certain cache mechanism, and are dispatched using the cache scheduling algorithm.

6. Usage Scenarios

A. When displaying vector data based on a range query, you can use vector-cut graphs entirely.

B. Sensory range and properties when displaying vector data, you can first return data based on the range, filter on the front end based on the attribute data, and finally show.

7. Areas to be resolved

The Open source Vector cutter tool is currently only able to cut WGS84 vector data, and it is unrealistic to convert any format data into WGS84 data. To solve this problem, it is an option to develop the vector cutting diagram tool. It is not very difficult to develop vector graph tools that can support point data, but it is difficult to develop vector-cutter tools that support line and polygon data. Further research is required for follow-up.

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A preliminary study of vector transduction in Webgis