or across the Alps,
is this <i>ΔH</i> equal?
That is the question that is posed in this quiz.
In 1995 Switzerland upgraded its national Geodesy,
in particular a rigorous system was defined for altitudes,
namely the system <i>RAN95</i> which is the new national altimetric network.
It is a rigorous orthometric system,
so the altitude measurements according to the theory of potential gravitational field.
We apply to the raw leveling measurements
the orthometric corrections
and we have now a perfect model for our altitude in Switzerland.
If we now compare the model defined in 1902, <i>NF02</i>,
with this new model,
we have the following map which shows these differences.
We can note in the plateau region,
so here in this area,
I see that the altimetry differences are near zero
or a few centimeters;
in contrast if I go to the Alp region
where the geoid is more disturbed by steeper slopes,
and well, in this case, I see that I may have these differences
between the two models up to 40-50 cm.
So these elements are now documented
and we have a rigorous network of altitudes for Switzerland.
When talking about documentation,
each of the points along the federal and cantonal leveling,
is documented in the records in which
we will find a certain number of information,
namely, identification of the point,
we have its region, we have a number corresponding to the national map,
then you will obviously have the approximate coordinates
to situate the point on a map;
associated with this, you have a photo that can identify this point in the landscape
in this case here, at the foot of a building,
we have an indication of the materialization,
in this case a pin
that was realized by the Federal Office of Topography
and we obviously have the value of the altitude here in the system <i>NF02</i>
with an estimated precision here of 3 millimeters.
We also see in this record
that there are regular updates and the controls here
of these altitude points, which are made by the Federal Office of Topography.
The measuring principle:
to be able to measure with the level,
it is necessary that the line of sight is horizontal.
We remind you here that the spirit level used to calibrate the level,
we have here the guideline;
once the bubble is in the upper portion of the tube,
the tangent in this upper portion here gives the guideline.
If the level is adjusted, this guideline will be parallel to the line of sight
and thus enable us to make measurements on an horizontal plane.
The measures is done on the staff;
the graduations of the staff are as following:
you have first the meters, the decimeters
and then the centimeters that are given here by the small black and white markers.
The millimeter will be estimated by eye with a precision of plus or minus one millimeter.
In this example here, we can say that we have one meter,
we have two decimeters
and we can count the number of centimeters starting from here to here
and we have seven centimeters,
and the estimation of millimeters we give here is about eight millimeters,
so that the height reading is 1,278 meters.