4.2　Indoor Work

4.2.1　According to the project planning，topographic maps of 1∶50，000 and 1∶100，000 for areas which the lines run through should be collected and topographic maps of 1∶10，000 shall be collected for complicated areas.For longer lines，topographic maps of a smaller scale may be collected.All collected topographic maps which have the same scale should have uniform coordinate and elevation systems.

4.2.2　Satellite remote sensing images，aerial photographs and Digital Elevation Model，where available，shall be collected and used according to the project requirements.

4.2.3　The collection and processing of satellite remote sensing images shall satisfy the following requirements:

1　The collected satellite remote sensing images should have a ground resolution of no more than 15 m，and the number of spectral bands should not be less than three.

2　The satellite remote sensing images shall meet the mapping requirements for images of 1∶50，000 or 1∶100，000.

3　Images which are taken recently and reflect the latest information should be selected.

4　The elements of images such as definition，cloud amount，hue，and contrast，shall satisfy the applicable quality acceptance requirements.

5　Any processing on imaging data such as pre-processing，rectification and fusion shall be conducted with professional remote sensing software.

6　The scale of maps produced from satellite images should be 1∶50，000 or 1∶100，000.Various geographic information should be indicated on the maps，including coordinate grids，main residential areas，roads，water systems，and planning areas.

4.2.4　The collection and processing of aerial photographs shall satisfy the following requirements:

1　The scale of aerial photographs shall be no less than 1∶30，000 for flat and hilly areas，and no less than 1∶40，000 for mountainous areas.

2　When using aerial stereopairs，photographing parameters and documents about acceptance of original results shall be obtained as well.

3　Aerial photographing data shall be processed with a digital photogrammetric system.

4　The results of aerial photographing processing shall include routing orthophoto map，digital elevation model，stereoscopic model，and so on.

4.2.5　The collected digital elevation model shall have its grid spacing of no more than 25m and the format shall be suitable for subsequent software processing.

4.2.6　The colleted digital elevation model may be used to produce skeletonized sectional data or graphic documents of the proposed route so as to meet the needs of pole and tower planning.