Creating DTM's where there is no 3D point data available, oftentimes means that one has to covert a old 2D AutoCad survey in order to process the DTM. The contours which are from old surveys are most probably a series of unconnected lines or polylines. Usually they are not connected because they have been broken around text or other drawing elements. These gaps can be fairly large and to connect hundred and possibly thousands of line segments and convert them to 3D polys for DTM processing sometimes can take up to 2 man days work, especially for large survey drawings. At present VW "compose" command is the answer but unfortunately for this to work the end points of all segments have to be coincident, therefore requiring much manual intervention to make them so. I have also found VW algorithm very slow if multiple lines with many segments are selected. The "compose" command, algorithm is not geared for such work. My suggestion is that NNA should rewrite this code to include a tolerance setting, whereby the large gaps can be bridged by interpolation. Also VW compose algorithms speed should be looked at and any redundancies removed so that it can handle multiple lines with many segments.
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Mbuck
Creating DTM's where there is no 3D point data available, oftentimes means that one has to covert a old 2D AutoCad survey in order to process the DTM. The contours which are from old surveys are most probably a series of unconnected lines or polylines. Usually they are not connected because they have been broken around text or other drawing elements. These gaps can be fairly large and to connect hundred and possibly thousands of line segments and convert them to 3D polys for DTM processing sometimes can take up to 2 man days work, especially for large survey drawings. At present VW "compose" command is the answer but unfortunately for this to work the end points of all segments have to be coincident, therefore requiring much manual intervention to make them so. I have also found VW algorithm very slow if multiple lines with many segments are selected. The "compose" command, algorithm is not geared for such work. My suggestion is that NNA should rewrite this code to include a tolerance setting, whereby the large gaps can be bridged by interpolation. Also VW compose algorithms speed should be looked at and any redundancies removed so that it can handle multiple lines with many segments.
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