No Picture in the Field …

The larger the topographic survey, the more complicated it was to code the linework. Since the older generation data collectors had very crude graphic capabilities, if any at all, any errors in the coding would only be found back in the office after the file was processed. It was common for field crews to return to the field to pick up more shots, or correct linework errors.

Figure 1 - Example SDR Coding

In Figure 1 we have a simple example of how you would code the edge of a road with SDR codes. EG1 represents the “string” or simply a list of points to be connected based on a common description, in this case EG1. At point 1, a linework code of ST indicates that a line should be started here. At point 100, the linework code STCV indicates the start of a curve and at point 102, EC indicates the end of the curve.

It is important to give some thought to how the user entered this into the data collector. There was no graphical picture to refer to, just a prompt asking them to enter a description for the shot. If they got distracted for whatever reason, it was very easy to forget what needed to be entered – for example, what if you forgot which line you were working on? “Am I working on line EG1 or line EG2?” The linework generated was only as good as the coding done in the field.

It was common for the surveyor to draw a rough sketch of their topographic survey in a field book or sketch pad. This was done so if points did not process correctly, they would have a sketch to refer to – it was a lot of extra work, but back then, you had no other choice.