VAPOR provides various support for geo-referenced data. The term "geo-referenced" means that there is a mapping (i.e. map projection) of the horizontal (X-Y) coordinates of the VAPOR domain to the earth's surface. VAPOR supports the four map projections used by WRF-ARW, including: Lambert Conformal Conic, Mercator, Polar Stereographic, and Rotated Lat/Lon (sometimes called Cassini). VAPOR also supports the standard Lat/Lon projection.
When model data is converted to a VAPOR VDC, or if model data is imported into VAPOR, the geo-referencing information is automatically derived from the data. Other (non-WRF) VDC's may also be geo-referenced. Instructions for specifying geo-referencing are provided in Preparation of Georeferenced Images.
VAPOR GUI's support for geo-referencing includes the following:
- In the VAPOR GUI Image panel, geo-referenced tiff images (geo-tiff images) are remapped to the VAPOR domain. These images and are displayed in the correct position in the associated VAPOR 3D scene relative to lat/lon coordinates on the earth's surface.
- When visualizing geo-referenced data, coordinates in the VAPOR GUI are often also provided as Latitude and Longitude coordinates. These include:
- In the Probe, Image, Contour, and 2D tabs, the lower-left and upper-right corners of the horizontal region, as well as the cursor coordinates in the tab's image, are presented in longitude and latitude.
- In the Region tab, the lower-left and upper-right corners of the current region are presented in longitude and latitude.
- In the Barbs tab, the lower-left and upper-right corners of the rake are presented in latitude and longitude
- In the View tab, the camera position and center of view are presented in latitude and longitude. Users may also specify these coordinates as lat/lon coordinates. When the camera position is specified in latitude and longitude, the camera will remain fixed in world lat/lon coordinates when the data domain changes over time (e.g. if the data domain is a moving WRF nest.)
The VAPOR installation package includes two command-line utilities, described in Preparation of Georeference Images, that make use of geo-referencing:
- getWMSImage.sh is useful in obtaining geo-referenced tiff images from Web Mapping Services, that can then be displayed in VAPOR GUI's Image panel.
- tiff2geotiff can be used to insert georeferencing information into a tiff file, converting it to a geo-tiff.
Images that are created by NCL can be converted to geo-tiffs and displayed in VAPOR. This process is described in the VAPOR tutorial Using NCL with VAPOR to Visualize WRF-ARW data .
