odin_dem

The odin_dem crate is a system crate that provides a digital elevation model (DEM). This crate is basically just a wrapper around the virtual GDAL VRT driver that is used to extract elevation data sets for given rectangular bounding boxes from a large mosaic.

1. Obtaining and Building the DEM VRT

Prior to using this crate you have to obtain respective source DEM image tiles, e.g. from https://apps.nationalmap.gov/downloader. Be aware that such data sets can be large (3dep 1/3 arc sec data for CONUS takes about 300 GB of disk space). The odin_dem crate provides the fetch_dem_files tool to download a file list of tiles via HTTP but this can also be done through publicly available 3rd party tools.

DEM data is available from several servers such as

• https://apps.nationalmap.gov/downloader
• https://earthexplorer.usgs.gov/
• https://opendap.cr.usgs.gov/opendap/hyrax/SRTMGL1_NC.003/N00E006.SRTMGL1_NC.ncml.dmr.html

We do provide sample file list for standard areas in the resource/ directory of this crate but be advised that such data might change - you should retrieve your own DEM tiles from the above sites.

Once the DEM tiles have been retrieved the GDAL gdalbuildvrt tool has to be used to create a *.vrt file from the downloaded DEM tiles. This *.vrt file is the basis for extracting the DEM for regions of interest such as incident areas, either as a synchronous function from within an existing server or through a simple standalong edge server.

Manual steps to retrieve tiles and build the VRT using the publicly available

• GNU wget
• GDAL gdalbuildvrt

cross-platform command line tools are:

$> wget -nv -i <file-list>
$> gdalbuildvrt <region-name>.vrt *.tif

2. DEM extraction

The basic function of odin_dem is the synchronous

#![allow(unused)]
fn main() {
fn get_dem (bbox: &BoundingBox<f64>, srs: DemSRS, img_type: DemImgType, vrt_file: &str) -> Result<(String,File)>
}

which takes the target Spatial Reference System (SRS), the bounding box (in SRS coordinates), the required result image type and the path to the *.vrt file (mosaic directory) to use and returns a std::fs::File of the extracted DEM.

This function can be called synchronously (no async operation involved) but - depending on the size of the VRT and/or the DEM to retrieve - it can take up to several seconds to execute.

The get_dem command line tool is a simple wrapper around this function.

3. Serving a DEM

Since the underlying DEM data for this crate does require large amounts of disk space we provide a simple stand alone edge server to run on dedicated machinery. This edge server needs to be configured with the path of the *.vrt file that references the tile data.