Abstract: Methods and apparatus for processing of data from GNSS receivers are presented. A post-processing engine and a post-processed accuracy predictor are described. The post-processing engine provides high accuracy GNSS (GPS) position determination with short occupation time for GIS applications. The post-processed accuracy predictor calculates during data collection an estimate of the accuracy likely to be achieved after post-processing. This helps to optimize productivity when collecting GNSS data for which post-processed accuracy is important. The predictor examines the quality of carrier measurements and estimates how well the post-processed float solution will converge in the time since carrier lock was obtained.