Data Exchange Standards (And Use of Run Length Encoding) : Direct Translation, Data Switchyard, and Neutral Format (Especially for GATE-Geospatial 2022)

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Data exchange is characterized as data import and data export. The data exchange process is not typically reciprocal, but rather, users import data purchased from data exporters (providers) . These are usually government agencies or commercial data sources. GIS users must know how to cope with the heterogeneous data environment. For data export, each internal data model must be converted to a specific file structure on disk or other media. The process is reversed for data import. The goal of data exchange is to transfer information to enable understanding of the phenomena being represented (Robinson, 1986) . There are three basic design strategies that can be used by data exchange software:

1. Data Exchange by Direct Translation

Data exchange between image systems using direct translation. This design is an effective method of data exchange because it involves the most efficient path between two systems. It is a good choice when only two systems are involved but requires an understanding of how the two systems work. Routines can be written to fit the data in the desired format. Problems with this design develop when more than two systems are involved. In such a case, alternative routines can be written for each system exchange.

Data Exchange by Direct Translation

2. Data Exchange between Image Systems Using a “Data Switchyard”

This method of data exchange avoids the factorial increase in the number of translation programs associated with direct translation. Data is converted into one internal standard. The software then translates data to the desired export format on output. Only two translation routines are required for all systems. This method works well when a large number of system translations are needed because it reduces the number of routines needed to convert the data.

Data Exchange by Converting into One Internal Standard

One important thing to consider when using the data switchyard is that attention must be paid to incoming and outgoing characteristics of the data so you don՚t lose information during the conversion. The central hub of data exchange must be all-inclusive so that you accommodate all the characteristics of the data.

3. Data Exchange between Image Systems Using a Neutral Format

When using the neutral exchange format, all parties must agree on one standardized common file. The advantage is that only two routines are required (one to read and one to write the exchange format) . Problems occur when a routine is unable to effectively encode and decode data to the neutral format and data characteristics are lost. The neutral structure must be all-inclusive and all parties must agree on a common implementation.

Data Exchange Using a Neutral Format

Common Technique for Data Encoding: Run-Length Encoding

Run-length encoding is a band sequential format that keeps track of both the brightness value and the number of times the brightness value occurs along a given scan line. For example, if a body of water were encountered with brightness values of 10 for 60 pixels along a scan line, this could be stored in the computer in an integer (213) format as 060010, meaning that the following 60 pixels will each have a brightness value of 10. Storing the two values 60 ar. 110 would require far less memory on disk or tape than storing 60 number 10s. However, if the data are exceptionally heterogeneous, with very few similar brightness values, this format is no better than the others.

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