Expert Land Surveyors in Derby

Relative accuracy refers to how accurate the survey measurements are in relation to each other. For example, the relative accuracy of a determined boundary plan should be +/- 10mm (0.010 metres). So the position of a fence, compared to a building corner, should be very accurate - even though overall the survey only needs to fit the Ordnance Survey map within 300mm (see above).

Imagine stopping to ask somebody for directions and being told "just keep going for 5 miles". To be safe, you then wait for another passer by and check with them. They say "It's 4.32 miles ahead". When you get there, you check the odometer and it reads 5.13 miles. The first helper was quite accurate, but not very precise. The second helper gave a very precise distance, but it wasn't accurate. An accurate AND precise answer would have been "it's 5.13 miles ahead".

This can range from historic aerial photography which can be used as evidence in a boundary survey, to high resolution drone survey images and video, which can be processed into 3d maps, models and orthophotos.

Land surveyors are now blessed with an abundance of technological advancements - but a good understanding of the source of errors is still paramount to delivering accurate and reliable survey data. These sometimes carry different names, but include natural errors (e.g. atmosphere,refraction), Instrumental errors (incorrect calibration of equipment) and human errors (e.g. poor vision). These must all be accounted for appropriately depending on the accuracy requirements of the project. Blunders, or Gross Errors are essentially mistakes often caused by fatigue or inexperience. They are typically the most catastrophic, due to their often large size but this also makes them very easy to spot with sufficient quality control procedures.

Photogrammetry is the process of image capture and processing to allow measurements to be taken from photographs. Commonly used at ground level for building facades and aerially from camera equipped drones, a number of survey and mapping tasks can be completed or benefited by this method.