OVR(Overview File)

GISBox is a one-stop 3D GIS data editing, conversion and publishing platform that supports editing in multiple GIS formats such as OSGB/GEOTIFF/RVT, converting to 3DTiles/Terrain and publishing.

Introduction

OVR (Overview File) is a file format used to optimize the rapid access and visualization of large-scale imagery or geographic data. It is commonly used in geographic information systems (GIS) as a pyramid file or thumbnail storage method for image data, helping users quickly load, view, and process image data at different resolutions. OVR files reduce the frequent access to original high-resolution data by pre-generating image data of different resolutions, thus significantly improving data rendering efficiency.

File Structure Characteristics

An OVR file is essentially a multi-layer image file containing data layers of different resolutions. It can be generated and stored in a variety of image formats. Its key features include:

**Resolution level: **Each level stores a reduced version of the image, for example, the original image is 100%, and the secondary level may be 50%, 25%, etc., forming a pyramid structure.
**Storage format: **OVR files are usually based on GeoTIFF format extensions and support a variety of compression methods (such as JPEG, LZW, DEFLATE, etc.).
Index information: Contains necessary metadata and index information for quickly locating a specific area of image data.
Association method: OVR files are usually stored together with the original image file, and the naming method is .ovr.

Pros

1. Efficient loading: Through pre-generated reduced data layers, OVR files can quickly load image data at different scales without reading the full high-resolution image.

2. Storage flexibility: Supports multiple compression algorithms and storage formats. Users can choose the appropriate method according to their needs to balance storage space and data loading speed.

3. Strong compatibility: OVR files are highly compatible with a variety of GIS software (such as QGIS, ArcGIS) and rendering engines (such as GDAL).

4. Easy to generate: OVR files can be easily generated through common tools (such as GDAL’s gdaladdo command).

Cons

1. Time cost of generation: The creation process of OVR files takes a certain amount of time, especially when the amount of original data is huge.

2. Increased storage space: Although compression methods can be selected, the multi-level pyramid structure will take up additional storage space.

3. Limited scope of application: OVR files are mainly used for raster image data, and have less support for vector data and other non-image types of data.

4. Additional management required: OVR files are stored separately from original image files, which may increase the complexity of file management, especially during data migration.