The Digital Globe 2011-12 Ortho Image Base Map, available in OLIVER, is an aerial-photo reference map that contains visible color, 30-centimeter pixel resolution ortho imagery from Digital Globe captured in spring 2011 and spring 2012. Imagery was captured statewide in spring 2011 in nine delivery areas. In Spring 2012, Berkshire County (the "Pittsfield" delivery area) and the town of Barnstable were re-flown, and the newer data are used in the imagery base map for these two areas (as shown on the index below). This base map features the most up-to-date ortho photography available at MassGIS.
Image acquisition consisted of "high value" and "standard" data (described in detail below), with the high value areas complying with more stringent standards. MassGIS created the ortho imagery base map such that the High Value imagery draws atop any Standard imagery where the areas overlap.
The image base map layer was cached (pre-rendered) for the Web using ArcGIS Server 10.1. The caching process greatly speeds the display of the imagery.
Accessing in Oliver
Add this base map to Oliver by choosing "Digital Globe Orthophotos 2011-2012" from the "Basemaps" button, found under the lower right corner of the map frame. The base map may be used alone, or any data or other pre-cached Tiled Layers from the Available Data Layers menus may be added to the map and drawn atop the imagery (see the sample images below).
MassGIS does not own this imagery. It is licensed from Digital Globe.
When displayed, the following disclaimer must be included:
"©Digital Globe, Inc. All Rights Reserved".
The imagery was part of Digital Globe's Advanced Ortho Aerial Program “Precision Aerial” high-resolution orthomosaics. These data serve as a high quality base map for Geographic Information Systems (GIS) or other applications that can display or analyze digital orthorectified imagery. Potential uses include asset identification, heads-up digitization, feature extraction, visual analysis, or any application that requires or benefits from a large area or regional orthomosaic imagery product.
These images were orthorectified using a digital elevation model gridded to the UTM projection and WGS84 datum, a set of GPS surveyed ground control points, a set of Airborne GPS measurements for each photo station, and a set of images acquired with a Vexcel-UCG Digital Camera, covering the area to be processed into digital orthoimagery.
All imagery was processed so that bright areas are not oversaturated, and shadow areas are not totally black. In addition, all imagery was color balanced across seam lines within each delivery area. Differences in color and brightness, however, are noticeable from one delivery area to another.
Three areas of the state, as shown in the index map at right, are considered "High Value Areas", which have stricter specifications when compared to the rest of the state, called "Standard Block Areas."
The following table outlines the different production specifications between the High Value and Standard Block imagery sets:
Values for Delivered Data:
High Value Areas Standard Block Areas Circular error at a 90% confidence level (CE90)1 2.7 m 4.1 m Radial Accuracy 95% confidence (NSSDA) 10 ft 15 ft Equivalent RMSE in X and Y 4 ft 6 ft Road Shear < 1.5 m < 3.0 m Leaf-off Yes Some leaf-out Minimum sun elevation angle 30° 20° Cloud Cover < 0.1 % < 0.5 % Cloud Shadow < 0.5 % < 2 % Haze < 0.1 % < 2 % Smoke < 0.5 % < 0.5 % Standing Water < 0.1 % < 0.5 % Snow < 0.5 % < 1 %
High Value Areas Sun Elev. Acquisition Dates Boston 31°-54° 2011-03-30, 04-08 Worcester 33°-56° 2011-04-08, 04-09 Springfield 42°-59° 2011-04-15, 04-18 Standard Blocks Sun Elev. Acquisition Dates Cape Cod and Islands 22°-61° 2011-03-30, 04-08, 04-18, 04-21, 04-29, 05-01, 10-08 Westport River Area 33°-61° 2011-03-30, 04-08, 04-09, 04-21, 04-29, 05-01 Springfield South 26°-66° 2011-04-09, 4-15, 4-18, 5-1, 5-12 NE Worcester County 31°-56° 2011-03-30, 04-08, 04-09, 05-01 Franklin/Hampshire Counties 26°-59° 2011-04-09, 04-15, 04-18, 05-01, 05-06, 05-12 Pittsfield (refresh) 39°-51° 2012-03-27 Barnstable (refresh) 30°-34° 2012-03-27
How horizontal accuracy is determined
Numerous image-identifiable targets are carefully surveyed to a very high level of accuracy, and the positions of the targets in the imagery are also measured.
RMSEx = SQRT(SUM(ximg –xmeas)2/n)
RMSEy = SQRT (SUM(ximg –xmeas)2/n)
Where the (ximg, yimg) are image-derived coordinates of the targets, and (xmeas, ymeas) are the measured locations of the targets in the field, and n is the number of points used.
RMSEr = SQRT ((RMSEx)2 + (RMSEy)2)
1CE90 = 1.5175 × RMSEr
Last Updated 7/10/2013