GML, SVG, VML comparison GML, SVG, and VML are XML-based tag language that describes vector graphics, which are XML word layouts, their syntax is not difficult to understand, but they have their own different uses and features. The following is a brief introduction.
GML (Geography Markup Language) is based on XML-based space information coding standard, which is proposed by OpenGIS Consortium (OGC), and has been supported by many companies such as Oracle, Galdos, MapInfo, Cubewerx, etc. The geographic data and graphical interpretation of the encapsulation is clearly separated by GML.
GML based on XML text represents geographic information Since GML can be seen as an XML, it is more likely to understand GML. And as XML is widely used, GML will benefit. In addition, the text is relatively simple, intuitive, easy to understand and edit.
GML encapsulates geographic information and its attribute GML based on geographic information abstract model, namely space entity feature and attribute package. Geographic features include a series of attributes and corresponding geometries, which generally consists of names, types, and values, and geometric information consists of basic elements such as points, lines, faces, curves, polygons. At present, GML is primarily limited to two-dimensional applications, which is extended to two-dimensional and three-dimensional space and topological relationships between characteristics. GML allows quite complicated features, such as nested rooms. For example, the airport is composed of taxi roads, aircraft runways, etc.
GML encapsulates the spatial geographic reference system space geographical reference system is the basis for geographic information system data processing. GML encapsulates the spatial geographic reference system, the main projection relationship, etc., ensures distributed processing scalability and flexibility.
GML can realize the distribution of GML of geographic data. GML is very convenient for the distribution of geographic data, but its role is limited to this, which can also be an important means of geographic data distributed storage. The main technical tools are XLINK and XPOINTER. The introduction from the top can see some advantages of the GML as a meta-language that describes spatial information. It can only describe the vector information and attributes of the space entity, and there are two different ways when displayed: L GML Drawà Displayl GML Transform à SVG, VML Draw àdisplay first channels need to directly operate GML data to analyze and display. The second pathway is to convert GML data into data in the corresponding graphics format, such as SVG, VML, and X3D. Then it is displayed by software that already exists in these graphics formats. Let's introduce SVG and VML.
VML (Vector Markup Language) is an XML word schedule initially developed by Microsoft, and now only IE5.0 is supported by VML. With VML, you can draw vector graphics in IE, so some people think that VML is the functionality of the brush in IE. Here is the advantage of VML: XML standard XML is recognized as a next-generation network tag language with infinite vitality, and VML has innate advantages. It is simple, easy to expand, and more. Support high quality vector graphics Display VML supports a wide range of vector graphics features, which are based on the path of the line and the curve description path. Two basic elements are used in VML: Shape and Group. These two elements define all the structures of the VML; Shape describes a vector graphical element, and groups are used to combine these graphics so they can be processed as a whole. The VML specification includes a large number of elements that support multiple different vector graphic features. Below is a predefined graphical element of VML: l Pathl line L POLYLINEL CURVE L RECTL ROUNDRECTL OVALL ARCL Group The image consisting of text, and can be integrated into HTML to represent images due to VML, which can be used to use very little. Bytes indicate complicated images. VML is compatible with HTML, by declaring VML namespaces in HTML and declares the processing function, you can use VML elements as other HTML elements, and display images on the client browser. Inside the VML tag, most of DHTML can define most of the properties and events, such as ID, Name, Title, ONMOUSEOVER, and more. Support interaction and animation but VML's function is not just drawing, he can also embed text in the graphics, and you can implement a hyperlink, and you can implement a certain animation function in scripting languages. VML appreciation
SVG (Scalable Vector Graphics) SVG is an open vector graphical description language based on XML. The SVG image is a document compatible with XML1.0, and the SVG element indicates some instructions that draw images. Readers explains these instructions and display the SVG image on the specified device. Use SVG to display a wide variety of high-quality vector graphics on the web, supporting a lot of features you imagined: geometric graphics, animation, gradient, filter effect, etc. The most critical is that it is also described using ordinary text! That is, this is a text-based image format specifically designed for the network. SVG is a synthesis of PGML and VML, so the advantage of VML has become the advantage of SVG, such as XML standard high quality vector image consisting of text. We can use any image processing tool, SME. We can use notes with any image processing tool. A SVG image can be generated. This may be incredible for the operators of image processing. In fact, think about it can also be understood that the vector image is generally described in algorithm instructions, and all description statements in the SVG image based on text, so it is also very easy to make two modifications and updates. " The upgrade is characterized here to get the appropriate reflection. In addition, there are some advantages over the SVG compared to VML: flexible file format SVG upgradeable features are not just in secondary modifications, but also in addition to many places, including the flexible file format described here. In the previous image, the text is saved in the image as a bitmap. After the image formation cannot be modified separately; this is improved in the PNG format, and the text can be used as a separate layer; SVG is more flexible Extended the file format of the image, which consists of three parts: vector graphics, bitmaps, and text. Such SVG can not only apply vector images and text objects, but also in the bitmap, it can make the effect of any other format image. Since the file format is text form, it can be easily modified at any time. And during the operation of the page, you can also make instant modifications for many parts, where the graphic description can also be reused. Support interaction and animation SVG supports SMIL (SYNCHRONIZED MULTIMEDIA Integration Language), making users freely completing some interactions with elements in SVG, thereby completing established targets, this is currently alone, alone, is done, needed The scripting statement in the web page is implemented. Support Character Find Find characters in "Pictures", becomes possible in SVG. This is impossible in this picture file in other formats. Support XLINK and XPointers can make hyperlinks between SVG documents. SVG has a large number of support mechanisms as the format of W3C organization. As Adobe has declared all the features that will integrate SVG in the launched Adobe image processing kit such as Illustrator, Photoshop, Golive, and Cyber Studio, Netscape Navigator and IE plug-in to allow them to directly support the svg file browsing. Netscape and Microsoft have also begun to enter the SVG field, which marks the future web browser will have a support function for the SVG file. Summary GML, SVG, VML has a close relationship with the vector graphics: GML adds the other attribute information of the entity while indicating the spatial information of the entity, is the coding standard of the spatial information and attributes of the entity, but it does not support direct Show graphics. The VML and SVG are displayed on the vector information indicating the graphics (ie what kind of style display vector graphics), which is a better format showing the vector graphics.
