Results visualisation in a thematic application based on geobrowser
The geobrowser of the portal uses the metadata of a job processing results to handle data visualisation on the map. It actually exploits the Terradue Cloud Platform API (see Production API here). Any results produced on the platform is analysed to provide with the map visualisation context. The results data are harvested once staged out of the production to find information such as quicklooks, geolocation, time, tags or any useful information. It also groups similar files to present them as one result entry with different format.
In this article, we describe this analysis process and give the main keys to format your workflows result.
As a first process, the data are listed to find all similar files for regrouping them as a single result entry. The filename without the extension is used for this aggregation.
For instance, if the result folder contains the following files
Flood_Map_20170405_max_extent.shp Flood_Map_20170405_max_extent.shx Flood_Map_20170405_max_extent.prj Flood_Map_20170405_max_extent.dbf Flood_Map_20170405_max_extent.png Flood_Map_20170405_max_extent.pngw Flood_Map_20170405_max_extent.properties Flood_Map_20170405_freq.tif Flood_Map_20170405_freq.rgb.tif Flood_Map_20170405_freq.tif.legend.png Flood_Map_20170405_freq.png Flood_Map_20170405_freq.pngw Flood_Map_20170405_freq.xml logs.zip
After analysis, the result metadata report will list only 3 items (datasets) but with many different types of data available for download
Flood_Map_20170405_max_extent |- Shapefile (zip) |- PNG |- PNGW |- Properties |- Legends (PNG) Flood_Map_20170405_freq |- GeoTiff |- PNG |- PNGW |- XML |- Legends (PNG) logs.zip
For the rest of the article, keep in mind that each group is now called a
dataset even if the group may contain only 1 file.
dataset in the job results, the harvester searches for a file that it can render as a raster via
WMS. Typically a geolocated images such as a
GeoTiff or any image geolocated with a
Here is the ranked (first found, first used) list of supported files that can be rendered as a
WMS layer and thus visualised on the map
- GeoTiff: georeferenced tiff raster (extent + projection referential)
- Shapefiles: set of files of vectorial spatial data
- Image + World file
- Image + properties file with the extent defined (see data properties later)
BUT when any of previous files is a raster AND contains RGB bands, it goes in priority for the map quicklook.
If any of the case listed above is found, the system creates a
WMS layer in the layer server and link it with the dataset. Therefore, when the geobrowser finds the link, it uses it as map quicklook of the dataset.
More precision about the raster rendering in WMS is given is the following paragraphs
Basically, the system handles the tifs in 3 ways according to the bands present in the file:
RBG(A): simple case where the the
RGBcolor model with an optional but recommended alpha channel information for transparency is used.
Paletteband : each pixel value is represented by a color in a palette. Usually 0 value as transparent color if
nodatavalue is not specified.
Grayscaleband : unique band with raw value. The system try to present the pixel value as a ramped grayscale palette. Usually 0 value as transparent color if
nodatavalue is not specified.
Image + World files
For any image file (preferably PNG with alpha band for transparency), you can geotag it with a world file. It will be a file with the same name as the image suffixed by
w (e.g. data.png --> data.pngw).
remark : if a geolocated PNG is found along with a greyscale GeoTiff, the system will choose preferably the PNG to be displayed as quicklook on the map.
A dataset can also contain a java properties file (key=value), named as the data file it described by replacing the extension or suffixing with
.properties, to give additional information about a result file. This additional information will be added into the metadata entry of the output file as metadata information. All keywords / value from the
.properties file are added as a table to the
summary element (used for metadata display on the geobrowser). Some keywords can set specific metadata such as:
date: in the format
startDate/endDatewith the date in ISO8601 format, it sets StartDate and EndDate values). A single date sets a instant time.
title: defines the title visible in the list of result
bbox: georeferences the dataset using the format
envelope: georeferences the dataset using the format
Env[minX : maxX, minY : maxY]
geometry: georeferences the dataset using WKT format
image_url(http://<my_image_url> or file://<my_image_path> : add a thumbnail image in the summary table)
copyright: add credits in the summary table)
When a dataset contains an XML file, the system tries to identify a known namespace and then exploit the metadata. The list of XML file format supported are:
ISO 19115-1:2014Geographic Information – Metadata
- Earth Observation Profile metadata model
In order to attach a legend to describe the dataset, a file suffixed with
.legend.png enables a map functionality that display the legend when the data is selected.
Footprint on the map
When displaying the results in the geobrowser and whenever possible, the datasets footprint are displayed on the map according to the harvested information in this ranked order:
extentderived from the file (Raster, CSV, kml, PNGW)
It is therefore recommended to avoid duplicated georeference (e.g. Geotiff + geometry) as they could result in odd rendering on the map.