Producing a CAD model will generally involve more than one method of data gathering. For example, total stations do not work well at very close range and they are cumbersome to use for small details. GPS is excellent for landscape survey but works less well for the details of standing architecture. Photogrammetry is difficult and expensive but excellent for details seen well in photographs. Tapes and traditional hand-measuring systems are slow but useful in areas that are inaccessible to total stations. Digitising existing plans, drawings or photographs allow existing data to be utilised. Each system has its drawbacks and each has its strengths.
When planning a data-gathering exercise a number of issues should be taken into account: