FAQs

“Can I see my house and my car in your TruEarth® 15-meter imagery? Why not?”
Our TruEarth® 15-meter imagery provides a complete, global, mid-resolution imagery baselayer containing over 3 TB of data. Detailed features such as cars and houses are not visible at the 15-meter-per-pixel level because they are much smaller in size than 15 meters. However, these details can be seen in high-resolution imagery at a 1-meter-per-pixel level or better.

“Is TruEarth® imagery map accurate?”
Yes. TruEarth® image products were created with tight geographic controls referenced back to raw image and data sources produced by USGS, NOAA, NASA, and other agencies. Here are the mapping particulars:

TruEarth® 1km:
Projection: Equi-rectangular (geographic, lat-lon)
Spheroid: WGS84
Pixel spacing: 30 arcseconds, 120 pixels per degree (nominally 1km)
Pixel locational accuracy: +/- 1,000 meters

TruEarth® 15-meter:
Projection: Equi-rectangular (geographic, lat-lon)
Spheroid: WGS84
Pixel spacing: 0.50 arcseconds, 7,200 pixels per degree (nominally 15 meters)
Pixel locational accuracy: +/- 50 meters

“What are the map scales of TruEarth® imagery?”
TruEarth® imagery is map accurate and suitable for use in cartographic projects at the map scales listed below:

TruEarth® 1km:
Map scale: 1:2,000,000 (the classical global and continental mapping scale)

TruEarth® 15-meter:
Map scale: 1:100,000

“How high off the Earth’s surface is the viewer when using the TruEarth® 1km imagery? TruEarth® 15-meter imagery?”
Based on the nominal resolving power of the human eye, which is 2 seconds of arc, the TruEarth® 1km imagery contains all of the visual detail that an observer would see if flying at about 1,700 kilometers (1,060 miles) above the surface of the Earth. TruEarth® 15-meter imagery takes you another 67 times closer, containing the visual detail that an observer would see if flying at 26 kilometers (16 miles or 84,000 feet) above the Earth.

In practice, atmospheric scattering, bluing, and turbulence coupled with cloud and fog distortions substantially diminishes the ground details actually seen at that altitude. In that sense, TruEarth® 1km and TruEarth® 15-meter imagery provide ground detail that will support scenes viewed significantly closer to the Earth’s surface.

Also, when TruEarth® imagery is being used in a CG rendering or animation, what really matters is not so much the human eye’s resolving power, but the resolving power of the video or film camera’s simulated optical system. For instance, if the scene is a wide shot, the resolving power of the simulated optical system is less than that for a close up. Therefore, TruEarth® 1km imagery can support typical on-orbit wide shots at a substantially closer altitude.

As comparison, the Space Shuttle nominally orbits at 300km (185 miles) above the Earth, the International Space Station orbits at 380km (235 miles) above the Earth, geo-synchronous communications and weather satellites orbit at 35,786km (22,220 miles) above the Earth, and the moon is about 367,000km (228,000 miles) away from the Earth.