Scale and Resolution

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In the map, scale and resolution are two commonly used terms. These two sizes determine the detail that the map feature describes the actual feature.

The Resolution referred in GIS is also called Ground Resolution or Spatial Resolution. It refers to the actual ground size (meter) that a pixel represents.

The map scale refers to the proportion between the map distance of measurement target and the ground distance. When calculating the map scale, we usually use the two parameters of ground resolution and screen resolution.

The screen resolution is also called pixel resolution. It refers to the pixels number that every inch contains on the screen, namely, Pixel per Inch. The default screen resolution is 96. Sometimes, it also uses pixel size to describe the screen resolution, such as the 0.28mm in WMTS standard.

The scale of SuperMap is defined by the ground resolution and the screen resolution according to the following formula:

Resolution: The map resolution or ground resolution refers to the actual ground size (m) that a pixel represents.
PPI, the screen resolution refers to the pixels number that every inch contains on the screen and the default is 96dpi (pixel/inch).
0.0254(m/inch) refers to the unit conversion between meter and inch.

Finally, this formula can be simplified as:Scale=0.0254/(Resolution*96).

The formula can be used to convert the scale and the resolution. For example, the interface of wmts-china uses the map classification specified in Geographic information public service platform electronic map data specification. The corresponding relation between scale and the ground resolution can use this formula to convert. See Adding_WMTS_Service_Interfaces.

Where, there is no screen resolution (pixel/inch) in the WMTS 1.0.0 standard. It uses pixel size (0.28mm=0.00028m) to specify. The conversion relation is:

PPI=1inch/(pixel size(m)/0.0254(m/inch))

For the WMTS 1.0.0 interface, pixel numbers in each inch: 1inch/(0.00028m/0.0254(m/inch))=0.0254/0.00028≈90.714

The default value of screen resolution can be modified by changing the system profile of SuperMap iObjects Java, namely, setting the following parameters in the %SuperMap iServer_HOME%\support\objectsjava\bin\SuperMap.xml as the needed values:

<CustomDPIX>96</CustomDPIX>
<CustomDPIY>96</CustomDPIY>

Notes:In the product before SuperMap iServer Java 6R(2012) SP1, the screen resolution is 76.2dpi by default.