The DWG format is an Autocad proprietary binary
format. When we want to load layers in
QGis from this format, multiple problems arise.
QGis uses the GDAL library to read / write external formats ,
such as DWG.
Firstly a clarification: do not confuse the DWG format and
DXF format. Often references for DWG / DXF
format are found which is a misuse of language. Both
formats are different . The
DWG format is the native format for Autocad software.
is a proprietary format and, in theory,
subject to license. The DXF format is a data
export format for Autocad software.
public and not subject to license.
As it is not easy to have an
updated documentation of this tool, in this article there is some useful
information to make the most of it.
We will discuss one by one the toolbar available options.
The available option under this menu item is Mapnik
Mapnik is a free map rendering
software that is used by OSM to draw the main map. OSM
uses Mapnik to draw 256 x 256 px squares, which are then delivered from the
tile server at tile.openstreetmap.org.
Mapnik tiles are generated and
stored on the tile.openstreetmap.org server. They are
calculated by a weekly extraction which is currently carried out on Wednesday
mornings (GMT / BST time zone). Each tile has its date of
creation and a simple marking of obsolescence (flag or flag) meaning that it is
ready to be recalculated. The rendering engine follows
these few rules:
When a user checks a tile on the OSM site, there is an automatic control to discover
if it is more than seven days older than.
If it is > seven days, it is ticked as obsolete (and , therefore, it will renew ).
A rendering process generates through a background process, a list of all the ‘obsolete’ tiles and; then
launches the new rendering for these tiles . Once finished , it requests for a
new list of tiles marked as obsolete .
Therefore , if no one is watching an area, it will not be updated often
. The tiles are recalculated according to interest / attention. To tick a tile as
obsolete does not include those tiles covering
the same area at higher zoom levels as obsolete . If you read ‘More OpenStreetMap coming soon …’ on a tile,
it means that there is no data for this one and that it is on queue to be recalculated
The other OSM rendering engine, Osmarender , is not accessible with
Since ArcBruTile no longer displays Google Maps , this option remains
the most used . No need to search for Bing Traffic options , you are limited to
basic displays .
Stamen is a company
in San Francisco, that has developed applications from
The Terrain option only covers the United States, while two
, Watercolor and Toner, cover the whole
The option Watercolor is used
for the map background. It applies effects on the
OpenStreetMaps coverage that gives the map a
hand drawing watercolor style.
The Toner option is a rendering black
and white high contrast OpenStreetMap data.
The following figure shows an example
both options jointly .
The reference website for coordinate systems
during World War II is Thierry Arsicaud’s website
: Notes on the “Modified
British System” used on the European Theatre of Operations during the
1919, Great Britain adopted in its territory the “British System”,
based on a Cassini-type map projection and the use of a
grid designed to facilitate the reading of the coordinates of the designated
points . This system was replaced
1927 by the “ British Modified System”, more
suited to cover large geographical areas and military operational use by
land or airlift
“British Modified” system was used during the second world war
by the British and American armies by being
to European, North African, the Near East and South East Asian operation
The following figure , from
Thierry Arsicaud’s website shows
the areas corresponding to the projections in course
World War II.
Here is an excerpt of the thesis defended in
November 2005 by Nicolas Guilhot, currently Lecturer in History and Management
at IFROSS – University Lyon 3, at the Graduate School of Social and Law
Sciences of LYON II University – LUMIERE. Those
wishing to consult the full text will refer to: http://theses.univ-lyon2.fr/documents/lyon2/2005/guilhot_n “As in many other areas of official
cartography, the first world war confirmed and accentuated the current
evolution in the projection systems used, and, even, if the preference for the
quality of conformity was not questioned, a projection system more suitable to
the new military needs was adopted: the war of position and the central role of
artillery fire according to maps had demonstrated the need for the military to
have, not only, geographical coordinates (degrees or grades), but also
rectangular (kilometric) in order to obtain the coordinates of a position
directly by their measurement on the map. However the polycentric system did
not allow assembling several sheets in a coherent system of rectangular
coordinates, a gap particularly problematic given the small area covered by the
breaks in the master plans.During the
war, the SGA had adopted Lambert’s projection in 1915, a consistent modified
With version 10.3, ESRI has announced a new possibility for the
geodatabase file: you can make them non-copy and you can give them a deadline
access date. Firstly, let’s discuss all you have to do, then a nice example of
how to make yourself absurd by living in isolation.
Joins between tables or layers pose virtually no problem when we have a
unique match between the two elements we are trying to join. For one record of
the reference table or layer, there is one or no record in the table or layer
to be joined. The resulting table or layer of the join can be treated as any
other table or layer.
Things always get complicated when the table or layer to be joined
contains more than one record corresponding to the same reference record. This
is called a 1-n relationship. We will discuss a hidden option that allows us to
answer some of the questions we have in the event of 1-n type space joins.
Firstly, let’s use a simple example.
There are two things you need to learn: the Python language and how to
use the ArcGis Python geoprocessing library. As for Python, tutorials abound. But
do not forget that you will only need some basics of the language. You will
basically string together already existing ArcGis tools.
Have you decided to get started? It’s time to put all the assets on your
side . It’s already enough complicated to learn a new language, it is useless
to add pitfalls! This is a checklist and a few tips to start smoothly. Firstly
, if you are accustomed to program and Python or another language leaves you
completely indifferent , just take a look at the few traps described below and tackle
down the Python tutorial of your choice .
On the other side, if you back
off, start by convincing yourself that it is not necessary to master Python in
order to use it for our tasks with ArcGis. It is quite possible to link the
processing in a Python script by only knowing the basics of the language .