diff --git a/docs/area.or.point.md b/docs/area.or.point.md new file mode 100644 index 00000000..1b3b2e23 --- /dev/null +++ b/docs/area.or.point.md @@ -0,0 +1,25 @@ +# Area or Point + +## TLDR + +Toitū Te Whenua (LINZ) has decided to standardise all of it's DEM/DSM GeoTIFFs into `PixelIsArea` + +## Background + +GeoTIFF files have a TIFF tag `GTRasterTypeGeoKey` that controls how to interpret pixels inside of the GeoTIFF. + +- `Pixel Is Point` the value of the pixel represent the point in the center of the pixel +- `Pixel Is Area` the value of the pixel represents the full area of the pixel for a 1m resolution it is 1m x 1m + +When a GeoTIFF is `Pixel Is Point` the TIFF's origin point is shifted by half a pixel, as the origin of the pixel is the center of the pixel. + +LINZ Elevation DEM and DSM's previously contained a mixture of `Point` and `Area`. + +From a [brief survey of other jurisdictions](./national-dem-dsm/README.md.md) they mostly all use `Area`. + +Area is also consistent with how [LINZ's Aerial Imagery](https://github.com/linz/imagery) is stored. + +## References + +- GDAL RFC: https://trac.osgeo.org/gdal/wiki/rfc33_gtiff_pixelispoint +- https://www.usna.edu/Users/oceano/pguth/md_help/html/PixelIsWhat.html diff --git a/docs/national-dem-dsm/README.md b/docs/national-dem-dsm/README.md new file mode 100644 index 00000000..9b40902e --- /dev/null +++ b/docs/national-dem-dsm/README.md @@ -0,0 +1,26 @@ +# Other Countries DEM/DSM Publication + +Before making recommendations on how to standardise New Zealand's DEM/DSM data, LINZ took a brief look at other jurisdictions and how they standardised their DEMs and/or DSMs. + +The key areas to look at were +- compression - what lossless compression was most common +- size - width and height of image +- file size - how big each tile is +- storage type (TIFF/COG/other) + +| Country | Name | Dimensions (px) | File SIze | Type | Compression | DataType | Nodata | CRS | PixelIsPoint | Comments | +| :---------- | :----------------------------------------------------------------------------------------------------------- | :---------------------: | --------- | ------------- | ---------------- | -------- | ------- | ---------- | ------------ | -------- | +| New Zealand | [National Elevation 1m DEM](https://data.linz.govt.nz/group/national-elevation/data/) | 480x720 | 1.4MB | GeoTIFF | LZW | Float32 | -9999 | EPSG:2193 | Area/Point | | +| Switzerland | [swissSURFACE3D Raster (50cm)](https://www.swisstopo.admin.ch/en/geodata/height/surface3d-raster.html) | 2,000x2,000 | 16MB | GeoTIFF (COG) | LZW | Float32 | -9999 | EPSG:2056 | Area | | +| USA - USGS | [National Map 3DEP](http://prd-tnm.s3.amazonaws.com/index.html?prefix=StagedProducts/Elevation/1m/Projects/) | 10,012x10,012 | 280MB | GeoTIFF (COG) | LZW (predictor3) | Float32 | -999999 | EPSG:26910 | Area | | +| USA - NOAA | [NOAA Digital Coast LiDAR](https://coast.noaa.gov/dataviewer/#/lidar/search/) | 8,463x6,475 | 189NB | GeoTIFF | LZW | Float32 | -999999 | EPSG:2229 | | In Feet | +| Australia | [Victoria 50cm DEM](https://elevation.fsdf.org.au/) | 10,000x10,000
Varies | 4MB | GeoTIFF (COG) | LZW | Float32 | -9999 | EPSG:7855 | | | +| Finland | [2M DEM](https://asiointi.maanmittauslaitos.fi/karttapaikka/tilausvahvistus) | 3,000x3,000 | 20MB | GeoTIFF | LZW | Float32 | -9999 | EPSG:3067 | | | +| Canada | [HRDEM - CanElevation Series](https://open.canada.ca/data/en/dataset/957782bf-847c-4644-a757-e383c0057995) | 10,000x10,000 | | GeoTIFF | LZW | Float32 | -32767 | EPSG:2958 | | | +| Norway | [Norway DTM1](https://hoydedata.no/LaserInnsyn2/) | 15,010x15,010 | | GeoTIFF | LZW | | | | | | +| France | [RGE ALTI 1m](https://geoservices.ign.fr/rgealti) | 1,000x1,000 | | Ascii Grid | | | | | | | +| Netherlands | [Actueel Hoogtebestand Nederland AHN3](https://app.pdok.nl/rws/ahn3/download-page/) | 10,000x12,500 | | GeoTIFF | RAW (Zipped) | | 3.4e+38 | EPSG:28992 | | | +| Scotland | [LiDAR for Scotland DTM](https://remotesensingdata.gov.scot/data#/list) | 10,000x6,000 | 132MB | GeoTIFF | LZW | | -9999 | EPSG:27700 | Area | | +| | | | | | | | | | | | + +This table was recorded in May 2023 and may now be out-of-date.