Gml Spatial Data Compression Mechanism

GML uses the XML standard (including geography characteristic geometry and attribute information) carries on the code to the geography information, mainly uses in transmitting, the exchange and the memory geography information. GML also already took the main network transmission the spatial vector data format. GML is based on the text, therefore reading with processing all quite simply, the versatility is strong. Regarding transmits the great data quantity spatial information, then must carry on the compression, But at present has not drawn up GML the compression standard.At present, some ordinary text compression algorithms already quite were mature, However these algorithms have not considered XML, the GML structure characteristic; But aims at XML specially some maturer compression system like XMill, Xpress, XGrind and so on, also all has not considered GML the characteristic; GML although its form is the XML form, but has its own remarkable characteristic, for example, the GML space data type many, the quantity is huge, Also therefore had decided the GML documents when make compression processing should have its special compression algorithm.This article base on the literature [20],fully unifies GML own characteristic, Proposed the GML GSC compression algorithm, the de-GSC decomposition algorithm which are suitable in the GML. This group of algorithm realized the GML documents non- damages compression processing, To the label, the attribute value, the attribute name, the spatial data in the document and so on many aspects have carried on compression processing. Simple introduction as follows:1. In GML space data the most essential factor is the feature object, It is the essential factor which has the certain geography significance. The paper unified the GML characteristic as well as the GML transmission characteristic, proposed the de-GSC decomposition algorithm. This algorithm is in front of compression algorithm GSC, does a step of pretreatment work, Withdraws the same name feature object to the identical document in, carries on decomposition processing to the GML documents, GML documents resolve into main documents, certain with feature sub-documents.2. Because the GML type many, the quantity is huge, after therefore had decided each decomposition obtains the GML documents analysis way uses flows the form the SAX way, Fully had considered the GML characteristic, has produced based on SAX the data stream environment GSC compression algorithm. This algorithm used the dictionary code method to make compression processing to the documents label; The element attribute name, the attribute value brings into line with in the algorithm consideration scope. Is processing the label and the processing data value intersection point, makes suitable processing, causes the algorithm to be more rigorous.3. The union geography space data compression algorithm, carries on the compression to in the GML space data part, applied the reference [ 26 ] center to state the algorithm to carry on to the spatial data has not had damages the compression.Based on this group of compression algorithm, this article has developed GML documents compression software GMLcompress, and has done the related some experiments. The experiment the identical GML documents after GMLcompress, XMill as well as some text compression tools compresses, carries on the comparison to the compression ratio. A series of experiments had proven the GMLcompress compression effect surpasses XMill as well as some text compression...