[Hexagon case-study] Map of South Africa in a single ECW file for public use

The Chief Directorate: National Geo-spatial Information CD:NGI) is mandated to supply geospatial information for the Republic of South Africa:

• Provide survey services
• Collect and maintain earth imagery and geospatial data
• Provide mapping services
• Provide geospatial information and professional support services
• Establish, maintain and provide a national spatial data infrastructure
• Provide management support services to the chief directorate
• Provide national geospatial information services at provincial level

GeoSpace flies the entire country of South Africa every three years. They create aerial photographs of the country for its customer, Chief Directorate: National Geo-spatial Information, the National Mapping Agency of South Africa. Mosaics of this imagery provide the basemap for the entire country used not only by CD: NGI, but also by other customers and, ultimately, by local governments. 

Hexagon Geospatial solutions were used in the project:

• GeoCompressor for compressing large size aerial photography images into accessible and easily updatable mosaics.
• ERDAS APOLLO offers compatible OGC services such as WMS and WMTS. This ensures that every standard GIS can benefit from a centralized geo-service.

Working in this environment, our clients often had hundreds of files that covered their Area of Interest, so it was not only difficult to find the ones they wanted, but also to load and display them all at once. Working with a single seamless mosaic saves time, disk space, and of course, money.

One Nation, One Basemap, Multiple Uses

GeoSpace flies the entire country of South Africa every three years. They create aerial photographs of the country for its customer, Chief Directorate: National Geo-spatial Information, the National Mapping Agency of South Africa. Mosaics of this imagery provide the basemap for the entire country used not only by CD: NGI, but also by other customers and, ultimately, by local governments. 

GeoSpace’s customers – such as CD: NGI, the South African National Roads Agency, and Statistics South Africa – provide census, transportation, and employment data for the populace of South Africa

Naturally, this data requires an accurate, current imagery basemap of the region. Not only does this provide the best backdrop, but the context provided by this imagery can be vital in understanding and drawing conclusions from the data

Too Many to Search, Manage, or Store

When your job is to cover a country the area of 1.22 million square km at 50cm GSD resolution, the amount of data that you generate can be staggering. Each of their approximately 440 flight missions captured 500 individual images and covered areas of about 2700-3000 square km each. After orthorectifying and mosaicking the images to a 1:10,000 scale, GeoSpace was left managing nearly 46,000 files. 

This much data caused both storage and management problems. Each 1:10,000 mosaic in uncompressed tiff format was approximately 500 MB in size. 

That represents a 97% savings over uncompressed imagery and 71% savings over JPEG-compressed imagery

Combined, the 46,000 files totalled 30 TB in size, which GeoSpace and their clients found to be nearly impossible to work with.

Working in this environment, our clients often had hundreds of files that covered their Area of Interest, so it was not only difficult to find the ones they wanted, but also to  load and display them all at once. And, there was the problem of the 30 TB of disk  space that was required to house all 46,000 files. All in all, it was just way too many files to have to deal with.

One ECW file, one tenth the size

Working with a single seamless mosaic saves time, disk space, and of course, money. To manage one image instead of 46,000 images has already been worth the effort. Our clients are very satisfied with the performance and manageability of the final ECW image

Updating the image is easy

The GeoCompressor solution also solved GeoSpace's problem of having to update the image as new data became available.

We fly new areas every month and need to update the currency on a constant basis

Updating the ECW file does not require them to recreate the entire mosaic. In addition to compressing the files into a single mosaic, GeoCompressor provides simple tools to update a particular region within an existing ECW file. This streamlines the workflow, ensuring that the latest data can be rapidly included in the mosaic without a large processing burden

Single data source for multiple customers

Since the base map is used by many different agencies, the final file must be rapidly distributed to thousands of users simultaneously. At CD:NGI, SANRAL and Statistics South Africa, the ECW image is delivered using ERDAS APOLLO, a server-based product from Hexagon Geospatial, to end users of desktop GIS and server-based technologies via Web GIS.

Fast file submission is only effective if everyone who needs the file can access the data. For CD:NGI, interoperability is of vital importance. ERDAS APOLLO offers compatible OGC services such as WMS and WMTS. This ensures that every standard GIS can benefit from a centralized geo-service.

Future plans: new base map, higher resolution

In 2017, the survey program began requiring that all new photos be taken at 25 cm GSD. This new requirement will bring the total uncompressed images to over 100 TB once the entire country is covered.

GeoSpace has already covered 200,000 square kilometers in the first four months and plans to cover all of South Africa by 2019. GeoSpace has covered 200,000 square kilometers in the first four months and is exploring all of South Africa by 2019. They started processing seamless 25-cm mosaics with GeoCompressor for each province, created another single ECW file from the resulting image.

GeoCompressor was used by GeoSpace to create a single compressed image to be used as a base map for all of South Africa.

This image can be used as a background for many different types of GIS data because it can be continuously updated and broadcast to thousands of users daily.

ECW compression reduced the overall file size by 97% without compromising and visual quality.

The visually-lossless, single-image mosaic of the Republic of South Africa provides a single point of truth that can served online and shared among different government departments

Using GeoCompressor and ECW as output format has significantly enhanced our productivity, and the cost saving on time and disk space is enormous. If you are thinking about solving these problems, I encourage you to "Go for it!".

Source: https://tinyurl.com/4unbfnj9

Softprom is a distributor Hexagon Geospatial.