Introduction

The GetDTMTile service will take x/y tile coordinates and deliver one DTM tile from Vexcel’s high-resolution continuous orthorectified Digital Terrain Model (DTM). This service is particularly useful for:

Modeling a Landscape
Mapping Hydrologic Networks (Flood/Drainage Modeling)
Surveying for Land-Use
Geomorphological Mapping

Technical Details

The GetDTMTile service is accessed by specifying the zoom level and tile coordinate(x,y) according to WMTS (Web Map Tile Service) specifications. The tiles returned will be WMTS-conforming, 256x256 pixels at 22 cm resolution in 32-bit GeoTIFF format. Each pixel will have an elevation value in meters (over the EGM2008 geoid).

Each tile contains the header object cache-control: max-age, set to 21515 seconds or roughly 6 hours. max-age can be used by the end client to reduce the number of times the same tile is downloaded within a single user session.

Output Tile Specifications:

WMTS Specification
256 x 256 pixels
32-bit depth
Pixel elevation in Meters (over Geoid EGM2008)
7.5-centimeter resolution (accuracy RMSE 22cm)
Image format: GeoTIFF
Output format: Single image file.

Base URL

This service will answer to requests on following URLs:

Mandatory parameters only - Defined as ordered http REST parameters:
https://api.gic.org/images/GetDTMTile/{zoom}/{tilex}/{tiley}?token={token}
Mandatory parameters only - Defined as Key Value Pairs:
https://api.gic.org/images/GetDTMTile?zoom={zoom}&tilex={tilex}&tiley={tiley}&token={token}
All parameters - Defined as a mix of REST and Key Value Pairs:
https://api.gic.org/images/GetDTMTile?zoom={zoom}&tilex={tilex}&tiley={tiley}&layer={layer}&year={year}&aoi={aoi}&token={token}

Parameters

Parameter	Parameter Type	Data Type	Description	Example Format	Notes

Parameter	Parameter Type	Data Type	Description	Example Format	Notes
Mandatory:
`zoom`	Ordered REST (1st) / Key Value Pair (KVP)	Integer	The zoom level of the tile. `16` `17` `18` `19` `20` - highest resolution	Ordered REST: `/20` KVP: `zoom=20`
`tilex`	Ordered REST (2nd) / Key Value Pair	Integer	The X coordinate of the tile. (Datum WGS84)	Ordered REST: `/358276` KVP: `tilex=358276`
`tiley`	Ordered REST (3rd) / Key Value Pair	Integer	The Y coordinate of the tile. (Datum WGS84)	Ordered REST: `/837688` KVP: `tiley=837688`
`token`	Key Value Pair	String	The token used to authenticate the requests.	`token={token}`	Use the Authenticate Service to receive a token.
Optional:
`layer`	Key Value Pair	String	The name of the layer. `bluesky-high` - Default - Wide area data collected with Condor in North America (20cm GSD) `bluesky-high-europe` - Wide area data collected with Condor in Europe (20cm GSD)	`layer=bluesky-high`
`year`	Key Value Pair	String	The collection year of the tiles expressed with 4 digits (e.g. 2021 or 2018)	`year=2023`	If year is unspecified, the result is a combination of the most recent information available with combined coverage of all existing data.
`aoi`	Key Value Pair	String	The identifier of the specific Area of Interest (AOI) of the information	`aoi=USUSCON1901`
`ChildAOI`	Key Value Pair	String	The identifier of the child Area of Interest (AOI) which contains the desired imagery. This parameter can only be used in combination with the `AOI` parameter in cases where the AOI contains several smaller collection regions. bluesky-high: `ChildAOI=n33w87-us-al-tuscaloosa-2019` bluesky-high-europe: `ChildAOI=n53e14-de-bb-templin-2022`	`ChildAOI=n33w87-us-al-tuscaloosa-2019`

Examples

Yulee Sugar Mill Ruins Historic State Park, FL - Demonstrating key value pair mandatory parameters, layer and year
https://api.gic.org/images/GetDTMTile?zoom=20&tilex=283675&tiley=436681&layer=bluesky-high&year=2023&token={token}

Parameter	Value

Parameter	Value
`zoom`	`20`
`tilex`	`283675`
`tiley`	`436681`
`layer`	`bluesky-high`
`year`	`2023`
`token`	`{token}`

Orthomosaic representation:

https://api.gic.org/images/GetOrthoImageTile/bluesky-high/20/283675/436681?year=2023&token={token}

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Clingmans Dome Observation Tower, Great Smoky Mountains National Park - Demonstrating RESTful mandatory parameters, and aoi

https://api.gic.org/images/GetDTMTile/17/35135/51666?aoi=USUSCON2101&token={token}

Parameter	Value

Parameter	Value
`zoom`	`17`
`tilex`	`35135`
`tiley`	`51666`
`aoi`	`USUSCON2101`
`token`	`{token}`

Orthomosaic representation:

https://api.gic.org/images/GetOrthoImageTile/bluesky-high/17/35135/51666?aoi=USUSCON2101&token={token}

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Arkansas River - Boone, Colorado - Displaying several adjacent DTM tiles

Tile-specific elevation scales:

Normalized elevation scale:

Orthomosaic representation

External Resources

Lat/lon to x/y/zoom coordinate Conversion:
- Programmatic Information: https://wiki.openstreetmap.org/wiki/Slippy_map_tilenames#Mathematics
- Online conversion tool: http://stefanosabatini.com/tools/tilecalc/
Tiff Code Libraries:
- LibTiff: a very popular library for opening Tiff Files: http://libtiff.org/
- Port of Libtiff for .NET: https://bitmiracle.com/libtiff/
Merging Raster Layers:
- QGIS: https://docs.qgis.org/3.16/en/docs/training_manual/processing/cutting_merging.html?
- GDAL: gdal_merge — GDAL documentation

Vexcel API Documentation

GetDTMTile Service - v1.4