Half of the earliest development of open-source GIS software was based on functions, features, and open interfaces that were not supported by a commercial GIS software. Therefore, different open-source GIS have different characteristics and are also suitable for different GIS application needs and development environments.

Main open-source GIS software

At present, the architecture of open source geographic information software has been very clear. Each project has a unique positioning, and each open source family has the corresponding functional characteristics of commercial software, which can achieve most of the functions.

About working on desktops and workstations:

The QGIS and Dig projects can fully meet the needs of ordinary cartographers and data collectors, completing functions such as simple editing and querying of geospatial information, and can replace expensive Arc GIS Desktop and Map Info Professional.

GRASS (developed by the U.S. Military Construction Engineering Research Laboratory) can fully serve as a professional operating tool for scientists and researchers. The complex spatial analysis algorithm and grid processing function can be comparable to ARC/INFO. It is the first GIS software on the Unix platform and, like other Unix software, has attracted the participation of multiple federal agencies, universities, and companies in research and development. In 1988, more than 1000 GRASS3.0 software packages were released. GRASS software has won three relevant awards from the federal government of the United States.

OSSIM (Open Source Soft Image) is a high-performance software used in remote sensing, image processing, geographic information systems, and photogrammetry fields. As a mature open source software library, it is designed to provide an integrated and optimal method and process for developers of photogrammetry and remote sensing software packages. The developers of the project have years of experience in commercial and government remote sensing systems and application software, and are funded by multiple government departments in the intelligence and defense fields in the United States.

The following is a list of commonly used open source GIS:

• Spatial database: PostGIS based on PostgreSQL database, MySQL spatial based on MySQL database, Ingres database with geographical target extension
• Geographic information servers: MapServer, GeoServer, Deetree
• WebGIS：OpenLayer、MapGuide
• Meta Data Catalog System: GeoNetwork
• Geographic information development library: GeoTools, JTS, TerraLib, Proj.4 (map projection library), GDAL, OpenCV
• Desktop GIS: uDig, GRASS, OpenJump, Quantum GIS
• Remote sensing image processing systems: OSSIM (Open Source Software Image Map), InterImage, PolSARPro
• 3D: WorldWind, OSSIMPlanet, OSG Earth, Cesium, Marble

The Use of Languages in Open Source GIS

The classification of open-source GIS software mainly includes C, C++, Python, Java,. NET, JavaScript, PHP, VB, Delphi, etc. according to the development language. Regardless of the language used, current open-source GIS software strives to support cross platforms to the greatest extent possible. Among them, 67.7% of open-source GIS software supports Windows, and 82.7% of open-source software can run in the Linux environment, which is related to Linux itself being an open-source operating system.

The Current Application Status of Open Source GIS Abroad

At present, the main users of open-source GIS software are universities, research institutions, and non-governmental organizations. At the same time, domestic GIS companies have also started holding open source GIS research and development competitions, focusing on the increasing application of open source GIS software. Based on the application of open-source GIS software both domestically and internationally in recent years, it can be seen that the current application of open-source GIS is still concentrated in universities and research institutions, and some industry users mainly use open-source GIS for WebServer applications. The open-source WebGIS platform has many applications, accounting for over 80% of open-source GIS applications. With more industry users becoming familiar and aware of open-source GIS, as well as the further stability and reliability of open-source GIS software, the application of open-source GIS will be increasing.

Copyright License System for Open Source GIS

The so-called free software refers to software that allows anyone to use, copy, modify and distribute freely, but it cannot guarantee free access to software. Free software is dual-mode in distribution/acquisition, that is, it can be shared free of charge or sold commercially.

The so-called open source software refers to the software's source code (the original files of the software program) that is completely open to anyone, that is, anyone has the freedom to obtain, use, copy, modify, and distribute the source code under the relevant license agreement specifications, but in order to protect the integrity of the initial source code. The relevant license agreement stipulates that there are certain restrictions on the freedom of the original creator to modify the subsequent behavior of the source code.

Free software and open source software have a wide range of common ground, which is generally referred to as "free and open source software"; Considering that they are increasingly involved in practical business activities today, we can also refer to them as "open source software".

Characteristics of Open Source GIS

Using open-source software has the following characteristics:

There is no need to pay expensive software purchase fees, which can save a lot of costs, upgrade for free, and widely promote applications.

Rich in resources, all the underlying layers are open, and users can freely choose to combine applications for seamless integration and transformation, fully meeting application needs and facilitating maintenance.

Open source software is designed and developed by a large number of top industry elites, with advanced design concepts and system architecture, new functions, and fast upgrades. Supports industry standards (OGC, SOA, J2EE, etc.), has good openness and scalability.

Because the underlying source program is open and there are no security issues (backdoor issues), it is beneficial for government, military, and security departments to adopt.

The advantage of open source GIS lies not only in its free nature, but also in its true meaning of freedom and openness. The former represents freedom and freedom, while the latter represents openness and extension. Unlike commercial GIS products, due to the free and open nature of open source GIS software, users can add features as needed. When everyone does this, the performance and functionality of open source products also surpass many commercial products, thus creating the advantages and vitality of open source. In addition, compared to general commercial GIS platforms, most open-source GIS products have cross platform capabilities and can run on systems such as Linux and Windows. Therefore, open-source GIS software has received increasing attention from academia and GIS platform manufacturers, becoming an important field of GIS research and application innovation.

License System for Open Source Software

The copyright licensing system for open-source GIS software usually adopts the open-source software licensing system. There are currently 58 open source agreements approved by the Open Source Initiative, among which the most famous licensing systems include GPL (the GNU General Public License), LGPL (the GNULesser General Public License), BSD (the Berkeley Software Distribution license family), and MIT (Massachusetts Institute of Technology).

1.There are certain differences between the GPL protocol and the BSD license.

The starting point of GPL is open source/free use of code and reference/modification/open source/free use of derived code, but modified and derived code is not allowed to be released and sold as closed source commercial software. The main content of the GPL protocol is that as long as a product using the GPL protocol is used in a software ("using library references, modified code, or derived code"), the software product must also adopt the GPL protocol, which must be open source and free. This is the so-called "contagion". Because GPL strictly requires that software products using the GPL class library must use the GPL protocol, for open source code using the GPL protocol, commercial software or departments with confidentiality requirements for code are not suitable for integration/adoption as the basis for class library and secondary development.

2.LGPL is an open source protocol designed primarily for the use of class libraries in GPL.

Unlike GPL, which requires that any software using/modifying/deriving GPL class library must use GPL protocol, LGPL allows commercial software to use LGPL class library through class library reference without the need for open source commercial software code, which enables open source code using LGPL protocol to be referenced, published and sold by commercial software as class library.

3.BSD is a protocol that provides users with great freedom and encourages code sharing, but requires respect for the copyright of code authors.

BSD allows users to modify and redistribute code, and also allows users to use or develop commercial software on BSD code for distribution and sales.

4.MIT is a license agreement as broad as BSD, and authors only retain copyright without any other restrictions.

The statement of the original license agreement must be included in the open source distribution version, regardless of whether you are publishing in binary or source code.

GPL, similar to Linux, is suitable for the market promotion and research and development support of open-source GIS software due to its ability to protect the interests of open-source institutions. Therefore, it is adopted by many open-source GIS platforms, such as GRASS, QGIS, and uDig. The statistical results of the copyright licensing system for open-source GIS software indicate that over half of open-source GIS adopt GPL copyright licensing. But there are also some open-source projects supported by non-governmental organizations based on MIT and LGPL, such as SAGA and Map Window.

OGC and OpenGIS

When it comes to open-source GIS, it is necessary to mention some data and interface standards of GIS. In addition to the development of technology, the compatibility of standards has played an important role in promoting the development of GIS, especially open source GIS.

The Open Geography Federation (OGC) is an international industry federation of 384 companies, government agencies, universities, and individuals involved in a concerted process to develop open geographic processing specifications. OpenGIS (Open Geodata Interoperation Specification, OGIS Open Geodata interoperability Specification) was proposed by OGC. Open interfaces and protocols defined by the OpenGIS specification support interoperability solutions, network, wireless and location services, and mainstream IT, so that complex spatial information and services can be used by authorized technical developers in various applications. The Open Geography Federation protocol includes the Network Map Service (WMS) and the Network Feature Service (WFS).

Geographic information systems classify OGC products into two major types based on complete and accurate software that follows OGC specifications. Geographic information system technology standards promote the exchange of GIS tools. Compatible products are software products that comply with the OpenGIS specification. When a product is tested and proven to be compatible through OGC testing projects, it is automatically registered as' compatible 'at that location. Real software products, which implement OpenGIS specifications but have not yet passed compatibility testing. Compliance testing cannot be applied to all specifications. Developers can register their products as implementation drafts or approved specifications, and OGC has the right to review and confirm each item.

The Development Trend of Open Source GIS

The development trend of GIS technology is open and interoperability, including open architecture, open data model and open ideas of developers. Open source GIS, as a new hotspot of GIS research, its trend will be to integrate openness, integration, standards and interoperability, and to develop from software to server oriented architecture (SOA). Through the construction of open-source GIS projects, the development cycle of GIS software can be reduced, software development costs can be reduced, software development efficiency can be improved, and the cost of using GIS platform software can be reduced, promoting the socialization and popularization of GIS. With the maturity of open-source GIS projects and the increasing number of applications, open-source GIS software has now formed a relatively complete product line, which is superior to commercial GIS platform software in some specific functions.

Although open-source GIS software lacks stability, practicality, and comprehensive functionality, its free and open advantages have led more and more enterprises, research institutions, and non-governmental organizations to invest in the research, development, and application promotion of open-source GIS software. Open source GIS software will become the best choice for theoretical teaching, scientific research, and GIS applications in small and medium-sized enterprises, and will also have better development.