GRAL
GSPF Reference Application Line

Some tasks such as computing user positions from satellite observations occur regularly in the day-to-day work of, for example, surveyors. For these tasks, complex software packages are often offered, but users are mainly interested in tools that are easy to use. Within the framework of the ESA GSTB-V1 project, IFEN had developed the Experimental IPF to provide a hosting structure for experimentation. Meanwhile this was developed further into the GSPF (GNSS simulation and processing facility).

This tool is very flexible and certainly able to fulfil many of the user tasks. But with its overwhelming capacities it is only suitable for expert users. IFEN also had developed the GNSS Software Series, a suite of tools each for a limited purpose, but with an intuitive MMI which was easy to use, even for the non-expert user. The idea was to combine the advantages of both of these tools. It should support experimentation by research engineers, but also be suitable for the common tasks of the surveying engineer. Simultaneously, algorithmic capabilities were to be extended further into geodetic applications.

GRAL is the prototype of a software package for processing GNSS observation data, providing tools to perform much of the day-to-day work for surveyors or research engineers working in the field of satellite navigation. The tools are based on a very flexible core software and enable the users to do their specific processing with only a minimum of interaction required.

Description

The GSPF software package consists of three basic elements: a user interface to create executable configurations, a processing kernel to execute these configurations, and a number of dynamically linked libraries (DLLs) to provide algorithmic modules that can be used in the configurations. Configurations are built of modules and their connections. The modules define algorithms to be executed, while their connections define the data flow between algorithms. The GRAL software was based on the GSPF, and the same basic architecture was adopted. A user interface provides the possibility to select the necessary settings, such as the definition of input data to be processed.

These settings are then translated into a GSPF configuration and executed by the processing kernel. Algorithmic modules used in the GRAL tools are supplied by means of DLLs. User interfaces, so-called default applications, are provided for common tasks that are expected in the day-to-day work of the standard user. Where this is not sufficient, e.g. for experimentation purposes, it is possible to start the GSPF user interface and adapt the default application configurations, for example with alternative algorithms or data flows, or with additional output. The activities necessary to accomplish this task were divided into three steps. First of all, the algorithmic functionalities of the GNSS Software Series were ported to GSPF algorithmic modules.

Then the algorithmic modules provided by DGC were added. Finally, suitable user interfaces were implemented, based on the functionalities of the GNSS Software Series. These user interfaces were developed so that there is as much commonality between them as possible.

Objectives

The objective of the GRAL project was to combine the advantages of both the GSPF and the GNSS Software Series in a single, newly developed software package. This new software tool should provide the expert user with the flexibility to put together their own configuration in order to experiment with algorithms and data flow, while simultaneously allowing the non-expert to easily perform their simple tasks.

A further objective was to extend the tool into the area of geodetic applications by adding more algorithmic models, which were to be implemented by DGC. It was intended to develop the software up to prototype status. Any further steps such as commercialisation of the software were not part of the project.