Automatic generation of elevation data over Danish landscape

C.1.3.3 Calculation options
C.1 Description of the analysis programme PIL
To make the programme run, a work directory c:/work, and a result directory c:/res must be established.
There are three different calculation options in the programme. The wanted calculation is chosen by the
user by marking:
1) Analysis and cut-out
2) Analysis and cut-out after local offset
3) Analysis and input reference file > level 3
1) Analysis and cut-out
With the calculation option ”Analysis and cut-out”, a differential calculation is done, and the statistical data
is calculated. All differences, which numerically exceed the gross error limit determined in level 3, are cut
out. If this calculation method is chosen, the cut-outs are done numerically without regard to a possible
offset.
If all points are to be included, the gross error limit in level 3 is set so high that there will be no differences
larger than this value.
2) Analysis and cut-out after local offset
If the choice is to do the calculation with the option ”Analysis and cut-out after local offset”, a possible offset
is determined first, and the cut-out is then done numerically from this offset.
If all points are to be included, level 3 is set higher than the greatest difference.
3) Analysis and input reference file > level 3
If this calculation option is chosen, the elevation differences are determined. Points, where the elevation
differences are numerically larger than the gross error limit indicated in level 3 after shift of offset, are
taken out, and elevation data from the reference file is put in instead of the grid point from the test file. For
example, a new, generated elevation model (test file) may be compared to an existing model (reference
file), and in case there is a difference in elevations greater than the value in level 3, elevation data from
the existing elevation model are put in. As reference file, the existing elevation model from the National
Survey and Cadastre might be used.
In case the two grids are not coincident, a bi-linear interpolation is done to move the grid points from the
reference file to the grid position for the test file.
A new grid file is generated which includes the automatically generated points plus put-in points. The new
grid file is placed in c:/work. It is then possible to compare this new grid file with the analytically determined
reference file. This offers an opportunity of analysing how good an accuracy can be achieved, if
grid points from an existing elevation model are included.
If, for example, a poor accuracy is achieved by the inclusion of the NS&C elevations, it is still possible to
avoid putting in the NS&S elevation data by using calculation option 2). This results in a grid full of holes,
where the cut-out points lie in the file ”Udklip.txt” or by self-chosen indication with the ending ”*ukl.txt.”. In
the files ”Udklip.txt” or ”*ukl.txt”, the cut-out points are found in list format. In the file ”Dummy.asc”, the
points in GeoCAD format are found. The external points will be assigned the landscape code 00 in here.
It is then possible to re-measure these points.
Use marked
For all three calculations options, it is possible to add ”use marked”. If an interpolation is included, the grid
point out of the four, which has an elevation difference larger than the one chosen in level 3, is cut out
(marked by the computer). This point will not be included in the interpolation of the neighbouring point. If
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