Volume 9, Issue 2
Tricks of the Trade
In and Out
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Updating a Geographic Database
Here is the example of Figure 2. Table 1 gives the measured coordinates and the coordinates of the database. First we choose pt3 and pt504 as a basis for the similarity transformation. Then we show that another basis, for example pt30 and pt31, will give the same result for the final coordinates of a measurement.
Table 1. Measured coordinates and database coordinates.
We choose and as a basis. The other control points are the points , , and . We transform the local coordinates of the control points and the free points (, , , and ) with respect to the chosen basis. Here we only work out .
We transform the local coordinates of the control points and the free points (, , , and ) with respect to the chosen basis. Here we only work out .
Next we compute the database coordinates of the new house with the following formula.
Here are the final coordinates of , , , and .
Table 2 summarizes the result.
Table 2. The transformed coordinates with respect to pt3 and pt504.
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