CERA release version 2015

CERA introduces GIS compatible shapefiles for hurricane season 2015

April 24th, 2015

Emergency managers, weather forecasters, and GIS specialists show a great interest in obtaining storm and non-storm related surge and wave information for their daily work. Online mapping interfaces for visualizing ocean model results and predictions are as valuable as GIS based files which allow the end-users to produce their own maps and imagery.

It is with great proud to announce the CERA release version for the hurricane season 2015 that will provide the ADCIRC results as GIS compatible shapefiles. This version is available for the CERA Northern Gulf system at http://cera.cct.lsu.edu and the CERA Atlantic Coast system at http://nc-cera.renci.org .

The CERA team always seeks productive feedback from clients. We endeavor to understand how their experience has been and how it can be improved. We take the requests for new features very seriously. Providing the ADCIRC model results as GIS shapefiles and making them available via a download functionality on the CERA website will fulfill a major request and is a critical and important step in the entire process of a real-time storm guidance system and an essential precondition for a wide acceptance in the community.

We have worked hard to produce clean geometries, multi-polygon features, an adequate splitting of the model output into shapefile classes and much more. The new CERA version allows you to download the data as shapefiles with an accompanying color file (lyr) to directly open the data in ArcGIS. You will also be able to save the data in the NetCDF file format.

We are looking forward to guiding you through the hurricane season 2015!

If you have any questions, please contact:

Carola Kaiser, email: ckaiser@cct.lsu.edu

CERA: http://coastalemergency.org


CERA “Shapes” Up

Using the matplotlib library to create clean geometries for GIS compatible shapefiles

By: Carola Kaiser

The Coastal Emergency Risks Assessment (CERA) team provides guidance about storm surge and waves for the Northern Gulf and the Atlantic Coast through its online portal (http://coastalemergency.org). In addition to that, we are working towards the goal of providing all layers in the shapefile format compatible with GIS software. This feature will be available for the hurricane season 2015.

We use the Python Matplotlib library (http://matplotlib.org/) to convert the ADCIRC NetCDF format into contours which can then be used to generate shapefiles. While working on the algorithms, the CERA team has discovered some specifics which are essential to produce clean geometries. Clean geometries in GIS terminology do not include any self-intersections, overlapping, or duplicate features and ensure the hassle-free usability for GIS specialists and emergency managers.

The CERA team would like to thank Ian Thomas from the matplotlib developer team for helping us create useable and valuable contours and geometries.

Here are the specifics and bug fixes that we have addressed:

  1. Matplotlib ‘tricontourf’ expects a data array, but does not support masked arrays. If you pass a masked array, it will be ignored. The triangulation should only contain triangles with valid data at all three vertices. The solution is to either remove invalid triangles from your ‘element’ array before creating the triangulation, or set a mask on the triangulation once it has been created.
  1. The created contours will contain one or more polygon exteriors and zero or more interiors. They can be in any order (an exterior is not necessarily followed by its interiors). This has to be explicitly tested in your own script. The CERA code takes care of this issue.

We provide the CERA Matplotlib contouring script as Open Source on the CERA GitHub website https://github.com/CERA-GROUP/cera_contour.

If you have any questions, please contact:
Carola Kaiser, email: ckaiser@cct.lsu.edu

CERA: http://coastalemergency.org