As everybody knows a GPS fix is obtained when there are at least 4 satellites signals received. But in urban canyons this is challenging and it could be only three on sight. When the GNSS receiver receives only three satellites, it is however possible to solve the navigation equations by assuming that the user’s elevation is known. This is where HiMap kicks in with a precise elevation database of worldwide urban areas. in addition, even with 4 satellites or more elevation data continues to be helpful to improve speed and accuracy
But using DEM is in itself a technological challenge. Indeed, the problem of a worldwide DEM is its huge size: a resolution of a few meters in elevation requires more than 40 gigabytes of storage, something that is impractical to store on a mobile device.
To solve this challenge CellGuide employed a compression technique using a 2-step approach. First, the database focuses on urban areas, and minimizes data for rural and ocean areas. Second, an advanced compression algorithm is used to further compress DEM data. The resulting database size is only a few megabytes.
HiMap can also be customized in terms of coverage, minimum size of cities in the database, DEM resolution and accuracy.
HiMap is now commercially available for CellGuide's ACLYS chip, ACLYS IP Core, and GPSense engine. the database is also available for licensing as an add-on to third party GNSS receiver manufacturers.