## ArcHydro : 2- Preparing a corrected DTM for hydrology – Part 1

A  Digital Terrain Model is a representation of the elevations of a territory. Each cell (pixel) of this DTM contains a height value. According to the generation means used for the surface and the allocated size ofr the cells, the height assigned to each one is more or less close to the exact reality.

If you want to use the DTM for a 3D view of the territory (ith ArcScene, for example), you can use it as it is and without any special precaution. By cons, if you want to model the water flow on the surface of this territory, the first thing to do, and the most important is to correct and adapt it to this objective.

What you will be doing during this step will define the quality of the results obtained regarding the watersheds and the different hydrological calculations available. Continue reading “ArcHydro : 2- Preparing a corrected DTM for hydrology – Part 1”

## Hydrology with a GIS, for the Dummies (that we are): calculation of the flow (4)

In the last three articles, we have discussed an example of application for each of the main methods for calculating the flow of a watershed. Although they are quite self-explanatory, we must go through a little theory to complete the subject.
First of all, let’s see what happens with the most widespread method, mainly used for all ArcGis hydrological calculations, the D8 method. Continue reading “Hydrology with a GIS, for the Dummies (that we are): calculation of the flow (4)”

## Hydrology with a GIS, for the Dummies (that we are): calculation of the flow (3)

In the two previous articles ( Hydrology with a GIS, for Dummies (that we are): calculation of the flow (1)   and   Hydrology with a GIS, for the nulls (that we are): calculation of the flow (2 ) we have approached three methods to calculate the flow of flow: two one-dimensional methods (D8 and Rho8) and a two-dimensional method (MFD).

Now we will discuss a variation of the most widespread method (D8) which we addressed first. Continue reading “Hydrology with a GIS, for the Dummies (that we are): calculation of the flow (3)”

## Bivariate display with ArcGis

It is not easy to visualize a bivariate map with ArcGis , i.e a map where the entities are categorized according to two variables located in two independent layers.

The colour assigned to each entity responds to a colour scale along two axes, X and Y:

Therefore each layer must be classified according to four classes. The entities which belong to the first class of each of the layers share the colour located at the bottom and left, those belonging to the strongest class of each layer will have the colour located at the top and on the right. Continue reading “Bivariate display with ArcGis”

## How to integrate free marine and terrestrial weather forecasts into QGis

In the previous article we discussed How to integrate free marine and terrestrial weather forecasts into ArcGis.
In this article we will discuss how to integrate weather forecasts into a QGis project . We will use marine forecast data for 8 days. These data is provided by the companies   NASCA   and   ACTIMAR , via the products  enav-forecast . Besides the software that employs and shares these forecasts for consultation and analysis ( enav-viewer ,   enav-forecast ,   enav-forecast for iPhone ,   enav -Pilot ), these companies also provides you with access to data via a WFS connection.

What data is available? Continue reading “How to integrate free marine and terrestrial weather forecasts into QGis”