For the restoration of monuments it is now becoming normal practice to carry out a preliminary study of the monument before starting any kind of work. The metric survey is one of the main operations required. For this reason, photogrammetry applications already have a large bibliography. In particular, digital photogrammetry is currently an effective system, providing different solutions of both the vector and raster type. For an 18th-century gate in the Malta fortification walls, many tests were carried out in order to establish a suitable procedure for the creation of digital orthophotos. A photographic metric product, showing maximum detail without subjective interpretation of the object and the conditions of the material, could be very interesting in supporting any restoration work. The use of automatic procedures is also particularly suitable where large-scale surveys have to be carried out on very large objects with homogeneous characteristics, as is the case with the Malta fortification Walls. The advantages of digital over manual processing lie in the possibility of measuring a very large number of points without fatigue and with a high level of productivity. Digital orthophotos require a digital surface model as input, but the production of a high-fidelity reconstruction of surfaces by automatic measurement of points in close range photogrammetry still remains an open problem. Particular difficulties are caused for instance by object details that are not imaged or with strong shadows, or by complete failure of the image matching algorithms. Discontinuities in the surface, very common in architectonic objects, complicate the generation of models and surfaces. Within this work, several tests using commercial software were carried out, to define the best parameters for the automatic generation of DSM (Digital Surface Model) related to the monument being studied. The initial tests are based on the different dimension of the search window and the consequences of this choice on the accuracy and reliability of the matching procedure. Further tests are related to the number of points needed to start the matching procedure: firstly, points have been entered following a regular grid, then a greater number of points from the analytical plotting have been entered. The results are compared, also taking in account practical and economic considerations. Finally, different aspects for the creation of representative surfaces of the object have been analysed due to the non planarity of the object, presence of linear discontinuities and noticeable overhangs. The above-mentioned tests lead to several general considerations regarding strategies for creating orthophotos as a suitable qualitative and quantitative tool for the restoration of a monument.