Request a SnakeGrid

To request a SnakeGrid parameter file for use on your project, please get in touch with us with details of the project for which you  require a SnakeGrid parameter file. This could be a verbal description, but ideally it would be  accompanied by a simple map.

Include in this any particular requests that you have for the characteristics of the grid. For  example, if you want it to match with an existing grid at any particular point (generally only  one is possible) or if it has difference branches that you would like to include on one single  grid.

We can normally accommodate branches a few kilometres apart on the same seamless  coordinate system. However, where different branches diverge more substantially we can  create a separate grid that is continuous at an indicated junction point. Within a few  kilometres of this junction point the two grids will be identical to within a few millimetres, thus  enabling continuous surveys across the join.

We generally aim to keep the scale factor distortion less than 20 parts per million (ppm) on  the track or road, which is compatible with surveys at 1:50,000 accuracy. If your requirements  are different to this, then let us know.

At this stage we shall be in a position to indicate the one-off price for the design of the grid.

The next stage will be to send us a coordinate description of the route of the project. This is  referred to as a set of “seed points” and simply means selected points along the route,  spaced at about 1 – 2 kilometres, with three dimensional coordinates (latitude, longitude and  height) in the WGS84 system or one of its equivalents (ITRF, ETRF89, NAD83, etc). These  only need to be accurate to about 100 metres in plan and 10 – 20 metres in height. It is  emphasised that the height needs to be above the WGS84 ellipsoid, and not above a local  land levelling datum. At the same time, you let us know your chosen name for the grid and its  associated parameter files. We can accommodate up to 16 characters (no spaces).  Examples might be, Route66_09 or BPV_09 for a route that went from Berlin to Vienna via  Prague. This then becomes a unique SnakeGrid identifier.

Once we have this information we then create a SnakeGrid parameter file that defines the grid  system to be used on your project. We can usually turn this around in a few days, but it  helps to establish the timescale when you first make contact.

We then send you a CD to install the software, together with a copy of the parameter file. We  also supply a report detailing the characteristics of the grid, the maximum scale factor  distortion to be encountered, and so on.