QGIS Whisperer

Search This Blog

My first QGIS map: the aid from Cyrene

Posted on December 16, 2017

1

Get link
Facebook
X
Pinterest
Email
Other Apps

Tanaka method or how to make shaded contour lines

Posted on December 07, 2017

Get link
Facebook
X
Pinterest
Email
Other Apps

Article moved to LandscapeArchaeology.org

Get link
Facebook
X
Pinterest
Email
Other Apps

Comments

My first QGIS map: the aid from Cyrene

Cyrene, Lybia Sometime during the reign of Alexander of Macedon a famine broke out in Greece. We don't have many documents reporting the gravity of situation; apparently Greece was suffering much during the tumultuous years just before and after the Macedonian conquest. The prosperous city of Cyrene , on the coast of today's Libya, came to rescue and sent an extraordinary quantity of grain, all in all some 40 to 50 thousand tons. Our main source of information is an inscription graved in marble and boastfully displayed in one of main public areas in the city centre. The inscription details quantities of the shipped grain: it is basically a shipping list mentioning 43 recipient communities and two women, mother and sister of Alexander himself. Such data just begs for a map. I didn't find a nice map of the Cyrenian shipments, so I made it myself, after the data in Garnsey (1998). The process of map design makes a perfect introduction to basic GIS cartography...

Looping through numpy arrays (e.g. moving/rolling window)

Numpy is the cornerstone of matrix based calculations in QGIS (and elsewhere). It does wonders with raster data (unless it hits the limit of available live memory...). A recurrent problem with Numpy is the implementation of various looping routines, such as the sliding window which is frequently used in image filtering and other approaches focused on cell neighbourhood. Below is the illustration of the problem: for each cell the window needs to query a specified neighbourhood (square, circular or other). Now, there exists a solution in the form of "stride tricks" within the Numpy library. However it is really cryptic (the SciPy cookbook uses the "devious" epithet); after all the very name "tricks" implies it being ... tricky. Numpy documentation actually discourages its use . We can do it in a more understandable manner - which also means more configurable - and without any particular computational overhead. Let's first examine the problem....

Powered by Blogger

My first QGIS map: the aid from Cyrene

Tanaka method or how to make shaded contour lines

Comments

Post a Comment