GDAL Virtual Raster (beta)
Open BetabetaVRTは、GDALによるラスターデータセットのXML記述です。VRTをレンダリング済みのGeoTIFFとともに単一のZIP（map.vrt.zip）にまとめます。そうしないとgdalinfo/gdal_translateが「map.tif not found」で失敗するためです。ベータ版：現時点ではオーバービューなしの単一バンドセットのみ対応しています。
主な機能
VRTフォーマットについて
VRT is a service format of GDAL: an XML file that contains no pixels but describes where they lie and how to read them. That is the usual way to stitch mosaics and redefine referencing without copying gigabytes of raster.
We hand over the VRT together with the raster itself: the map.vrt.zip archive holds the XML description and the rendered map as a GeoTIFF. That was done deliberately — a lone .vrt would refer to a file you do not have, and gdalinfo simply would not open it.
The XML records the WGS84 coordinate system, the georeferencing (corner coordinates and pixel size) and three RGB bands, each pointing at the corresponding band of the GeoTIFF. The format is in beta status: it is one set of bands with no overview pyramids, and the raster itself is a flattened picture of the map rather than vector layers.
VRTファイルを開けるプログラム
次のプログラムおよびアプリケーションは、OSM2CDRからエクスポートしたGDAL Virtual Raster (beta)（.vrt.zip）ファイルを開き、編集し、利用できます：
Format specifications
- Open standard
- 2D only
- Lossless (no quality loss)
- No attributes
- Output: 1 file
- GDAL Virtual Raster (.vrt). XML descriptor referencing source rasters; lazy mosaicing without copying pixels.
VRT地図を利用するユーザー
VRTのエクスポート方法
エクスポート後の開き方
- Unpacking is a mandatory first step: map.vrt and map.tif must lie next to each other in the same folder, since the reference inside the XML is relative.
- GDAL — gdalinfo map.vrt will show the size, the referencing and the bands; gdal_translate will convert the set into GeoTIFF, PNG or COG.
- QGIS — Layer → Add Raster Layer and pick map.vrt; the layer will land in its place by coordinates.
- A mosaic — your own .vrt over several rasters is assembled with gdalbuildvrt out.vrt tile1.tif tile2.tif, if the map has to be stitched with other data.
- Editing by hand — VRT is plain XML: the path to the raster, the referencing and the band descriptions can be fixed in a text editor.
VRTの人気地図
GDAL Virtual Raster (beta)の地図エクスポートを入手
OpenStreetMapからプロフェッショナルなVRT地図をダウンロード。即時生成、任意の範囲に対応。