To conclude the creation of our own source of elevation , started in
previous articles( Starting with ArcGis
Pro: create your own
source of elevations ( 1) and (2)
) we are
going discuss the use of the raster calculator with ArCGis Pro.
We have two different areas in our work surface:
- a terrestrial area
- a marine area
We
have finished calculating the marine area with the command Topo to raster:
We will create a continuous DEM by following the following steps :
1-cutting the marine DEM with the ” sea ” polygon
2-cutting of the terrestrial DTM with the ” earth ” polygons
3-filling of the empty cells eventually created in the boundary of both areas (
land-sea )
Cutting the marine DEM with the “sea “ polygon
We will select the polygon “sea” of
the polygon terrestrial-sea layer ( in Map tab of the ribbon “Select”
button)
In the Geoprocessing window , click on Toolboxes and go to Data Management
Tools -> Raster -> Raster Processing -> Clip
You
must indicate that you want to cut the raster with the layer terrestrial_sea AND
check Use Input Features for geometry Clipping. This makes ArcGIS Pro to use,
only, the entities selected for cutting , in this specific case, the ” sea
” polygon.
Cutting
of the
terrestrial
DTM
with the
“earth” polygons
We
start by loading the whole terrestrial area DTM in the view window
We will perform the
same operation as before, but by using the “terrestrial” polygons.
Since the ” sea ” polygon is always selected, just click on the terrestrial_sea layer in the legend window -> Select -> select switch to invert
the selection and get all “earth” polygons
selected.
The
Raster Clip command is executed again , but this time on the srtm raster . It just
replaces the name of the input raster.
The result is loaded
into the view :
Now that we have both sections of the desired DTM, we need to join them in an unique raster. To that end we will use the ArcGis Pro Raster Calculator .
In
the Geoprocessing window, return to the Toolboxes and click Spatial Analyst
Tools -> Map Algebra -> Raster Calculator
The formula is the
following :
Con ( IsNull (“ MntMer
“), “srtm_36_031_Clip”, “MntMer”)
In French , this
means that, depending on the following condition (Con):
if the pixel of the MntMer raster is empty ( IsNull (” MntMer “)), we will retain the
value of the terrestrial raster , if not we will retain the value of the sea
raster.
The
only problem with this formula
is that some pixels on the terrestrial-sea boundary
are empty on both input
raster (the pixels that appear in white):
It is enough to replace these null values by 0, which corresponds to the height of the coastline.
To this end , in the raster calculator you must type the formula
Con ( IsNull (“Mntcommun1”),
0, “Mntcommun1”)
The
result is the following :
Now we can click on
the Scene tab and edit the dtm used for the 3D
view .
By
default the Aerial image appears in
the dtm provided with ArcGis Pro:
By clicking the ribbon, MAP tab, Add Preset button-> Ground and
pointing to dtm that we have just created, we get:
Even if it is subtle enough , we can see that the absolute
flat surface of the marine part of the first picture is replaced by the actual seabed elevation.
