GetDSMTile Service - v1.4
- Scott Jonker
Introduction
The GetDSMTile service will take x/y tile coordinates and deliver one DSM tile from Vexcel’s high-resolution continuous orthorectified Digital Surface Model (DSM). Previously, Vexcel’s DSMs were only available via full-size GeoTiff images but now, with the DSM API, a whole world of applications opens up with on-demand access to the Surface Model, such as:
Determining the height of an exhaust pipe on a building
Measuring the north-facing facet of a roof
Detecting the footprint of a building,
Calculating the volume of the building
Identifying individual roof slopes and sizes
Technical Details
The GetDSMTile service is accessed by specifying the zoom level and tile coordinate (x/y) according to WMTS (Web Map Tile Service) specifications and is available for layers bluesky-high (zoom 16-20) and bluesky-ultra (zoom 16-21). The tiles returned will be WMTS-conforming, 256x256 pixels up to 7.5cm or 20cm resolution (layer dependent) in 32-bit GeoTiff format. Each pixel will have an elevation value in meters over the EGM2008 geoid. All tiles will align perfectly with other Vexcel tile data (Orthomosaic tiles, Near-Infrared tiles, etc.) as well as tiled data from other third-party WMTS-conforming services. The GeoTiff contains several extended tags: 33550 contains pixel size information, and 33922 contains the x/y location of the tile on earth (in meters). More information and code examples for these extended tags can be found in the Ground Truth Blog linked in the External Resources section.
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
EPSG: 3857
32-bit depth
Pixel elevation in Meters (over Geoid EGM2008)
Layer dependent 7.5- or 20-centimeter resolution (accuracy RMSE 22cm)
GeoTiff image format
Base URL
This service responds to requests from the following URLs:
Mandatory parameters only - Defined as ordered http REST parameters:
https://api.gic.org/images/GetDSMTile/{zoom}/{tilex}/{tiley}/?token={token}Mandatory parameters only - Defined as Key Value Pairs:
https://api.gic.org/images/GetDSMTile?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/GetDSMTile/{zoom}/{tilex}/{tiley}?layer={layer}&year={year}&aoi={aoi}&token={token}
Parameters
Parameter | Parameter Type | Data Type | Description | Example Format | Notes |
|---|---|---|---|---|---|
Mandatory: | |||||
| Ordered REST (1st) - or - Key Value Pair (KVP) | Integer | The zoom level of the tile.
| Ordered REST: |
|
| Ordered REST (2nd) - or - Key Value Pair | Integer | X coordinate of the tile. (Datum: WGS84) | Ordered REST: |
|
| Ordered REST (3rd) - or - Key Value Pair | Integer | Y coordinate of the tile. (Datum: WGS84) | Ordered REST: |
|
| Key Value Pair | String | Token used to authenticate the requests. |
| Use the Authenticate Service to receive a token. A token will temporarily be stored in cache and may be omitted on subsequent calls. |
Optional: | |||||
| Key Value Pair | String | The name of the layer. The DSM is only served for
|
| |
| Key Value Pair | String | The collection year of the tiles expressed with 4 digits, (e.g. 2021 or 2018). |
| |
| Key Value Pair | String | The identifier of the specific Area of Interest (AOI) of the information. bluesky-ultra: bluesky-ultra-europe: bluesky-ultra-japan: bluesky-ultra-oceania: bluesky-high: bluesky-high-europe: |
| |
| 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 bluesky-ultra: bluesky-ultra-europe: bluesky-ultra-japan: bluesky-ultra-oceania: bluesky-high: bluesky-high-europe: |
| |
Examples
Santa Monica Pier - Santa Monica, California - Demonstrating layer and year https://api.gic.org/images/GetDSMTile/21/358276/837688?layer=bluesky-ultra&year=2022&token={token}
Orthomosaic representation:
https://api.gic.org/images/GetOrthoImageTile/bluesky-ultra?zoom=21&tilex=358276&tiley=837688&year=2022&token={token}
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Residential Home - Los Angeles, California - Demonstrating aoihttps://api.gic.org/images/GetDSMTile/21/359366/836944?aoi=us-ca-losangeles-2021&token={token}
Orthomosaic representation:
https://api.gic.org/images/GetOrthoImageTile/bluesky-ultra/21/359366/836944?aoi=us-ca-losangeles-2021&token={token}
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Griffith Observatory - Los Angeles, CA - Demonstrating Several Adjacent DSM tiles -
Tile-specific elevation scales:
Normalized elevation scale:
Orthomosaic representation:
https://api.gic.org/images/GetOrthoImageTile/bluesky-ultra/18/44928/104614?aoi=us-ca-losangeles-2021&token={token}
External Resources
Lat/lon to x/y/zoom coordinate Conversion: https://wiki.openstreetmap.org/wiki/Slippy_map_tilenames#Mathematics
Tiff Code Libraries:
LibTiff: a very popular library for opening Tiff Files: http://libtiff.org/
port of Libtiff for .NET: https://bitmiracle.com/libtiff/
The Ground Truth blog announcing Vexcel’s GetDSMTile service: Digital Surface Model Now Available via API
Merging Raster Layers:
Need help? Create a support ticket | support@vexcelgroup.com