If a higher horizontal accuracy is required, following requirements exist:

- For maximum of 3 m positional (RMS) error: All (handheld) GPS have to be equipped with a high accuracy chip (e.g. Sirf III for PDA/GPS), all image data have to be re-georeferenced with newly collected ground control points, newly acquired images have to meet the Precision level of imagery (CE90: 4.1 m, RMS: 1.9 m), collected vector maps have to be checked and also re-georeferenced (either with conversion parameters, or re-calibrated)

- For a submeter positional (RMS) accuracy: GPS have to be single-frequency GPS retriever (considerably more expensive and complex) or data from handheld GPS to be postprocessed, if synchronous GPS data from a reference base station within a distance of less than 50-100 km are available), all image data have to be re-georeferenced with newly collected ground control points, newly acquired images (only QuickBird) have to meet the PrecisionPlus level of imagery (CE90: 2.0 m, RMS: 0.9 m), collected vector maps have to be checked and also re-georeferenced (either with conversion parameters, or re-calibrated)