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element called the Precision Processor. In this instrument the original ERTS image is compared 
with a library of preselected ground control point images. By automatic correlation the ERTS image 
coordinates of the control points are measured. The computer then determines the constants ofa 
polynomial describing the image distortions. On a second stage the original image i$ rescanned in 
25 mm square blocks and reprinted in the correct position. A single image of Lake Tahoe, Califor- 
nia, acquired by the MSS two days after spacecraft launch was processed in this manner and repro- 
duced lithographically. This proved to be a rather slow and cumbersome procedure and adversely 
affected the resolution of the final product. In addition it was found that the geometric integrity of 
the original MSS images was far better than had been expected. Precision Processing has now been 
virtually abandoned. 
The next approach was simply to match the images to an existing line map. For small map 
scales this worked surprisingly well. The Soil Conservation Service prepared a 1:1 000 000 scale 
mosaic of the entire United States on the Albers equal area projection. The individual images were 
subjected to transformation in a rectifier to obtain the best fit to the existing base map [4]. No 
accuracy check was made on this map. 
A similar technique was applied to produce a standard 1:250 000 scale quadrangle of the 
Phoenix, Arizona, sheet on the Universal Transverse Mercator (UTM) projection. Parts of 5 ERTS 
frames were mosaicked to produce the photo image base which met NMAS for planimetric position 
Although Arizona is one of the most photogenic areas in the country the resolution was not really 
adequate for this scale, and similar efforts at 1:250 000 scale in less photogenic areas were consi- 
dered unsatisfactory. 
Another black-and-white mosaic at scale 1:500 000 for the whole state of Arizona was 
assembled on the Lambert Conformal Conic projection with a fitted UTM grid. Versions were prin- 
ted both without and with the planimetric line detail from the standard map. One of the most success- 
ful products utilized the image base printed in sepia with the planimetric detail in standard map 
colors. One feature which may be noted is that the Southeast illumination on ERTS pictures is 
opposite to that normally employed for relief representation. 
Making cartographic products using the color imagery available from ERTS-1 is conside- 
rably more difficult than using single band black-and-white imagery [5] . The first printed color 
ERTS map was for the State of New Jersey assembled from three consecutive scenes from a single 
orbit. 
The New Jersey mosaic was prepared by first enlarging the individual black-and-white 
images from bands 4, 5 and "7 to nominal 1:500 000 scale on continuous tone stable base film. The 
images from band 5 were then mosaicked by contact printing to à new film using a set of exposure 
windows to mask the frames and bleed together the adjoining images. This eliminated the mosaic 
match line and the need to rephotograph a paper mosaic with consequent loss of image quality. Mo- 
saics of band 4 and band 7 were assembled similarly using the band 5 mosaic as a control base for 
positioning the images of the other bands. The three separate bands were then screened for litho- 
graphy and the color image appeared only during the final printing. 
During this process no deformation was applied to the original ERTS images. The resul- 
ting map is therefore on no recognized map projection. In order to place the UTM grid on the map, 
a number of ground control points were identified and their coordinates measured on the map. An 
11-parameter projective transformation was then computed to achieve a least squares fit between 
the image and the UTM grid [6] . The coordinates of the grid intersections were computed and the 
grid was ruled. The grid lines are Straight, but they are slightly non-parallel and of slightly diffe- 
rent spacing, but the difference cannot be visually detected. Any UTM coordinates measured from 
the nearest grid intersection will be quite accurate. However the overall accuracy of the map did 
not quite meet NMAS for 1:500 000 scale. 
A second color image base map has been compiled for the whole state of Florida. This 
state extends across 7 ERTS orbits, lies in two UTM zones, and 18 ERTS scenes are required for 
complete coverage. A planimetric block adjustment of the images was computed to determine the 
conformal enlargement of each image constrained to fit the adjacent images as well as the control. 
The results were surprisingly good with an rms of 105 m. The estimated accuracy of well-defined 
points referenced to the fitted UTM grid on the finalmap is 150 m which meets NMAS for scale 
1:500 000. 
-~ 81 ~ 
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