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HYDROGRAPHIC APPLICATION OF PHOTOGRAMMETRY U.S.A-5
the outer edge; thus, the junction errors are smaller than graphic errors. Seldom
is any new horizontal control established for nine-lens plotting: existing control
is sufficient, particularly as the method is very tolerant as to the relative loca-
tion of the control. Vertical bridging is not attempted except for preliminary
or reconnaissance maps.
Multiplex bridging is done in a normal manner for as many as 10 models.
Vertical bridging is not attempted as elevations are furnished in each of the four
corners of every model, either by field methods or by means of stereoplanigraph.
Ordinarily, all control, horizontal as well as vertical, is furnished to the Kelsh
plotter, either by field methods or by stereoplanigraph. Where neither of the
auxiliary methods is convenient, model templet bridging is performed. The
model templets consist of etched lines on transparent stable plastic. Inasmuch
as the mapping areas between control are not very large, the number of templets
is small enough so that they can be manipulated by hand without undue diffi-
culty, and the slotted type of templets is not required. The Kelsh pantograph is
not used in making model templets because of the possibility of added system-
atic errors. If the templet scale is too large, it is reduced by drawing the
radial lines nearer the radial center.
Stereoplanigraph triangulation is being done continually, both vertically
and horizontally, at various scales. In fact, the stereoplanigraphs are being
used almost exclusively to furnish control by aero-triangulation for Multiplex
and Kelsh compilation. The general method is the same as that of the Army Map
Service, the principal difference being the use of International Business Ma-
chines for a linear transformation [5] of instrument coordinates prior to the
graphic analysis of systematic errors.
The Coast and Geodetic Survey looks forward to even more useful and valu-
able applications of aerial photography in its hydrographic service. Interest is
expressed concerning the application of 120 degree photography in addition to,
or in place of its nine-lens camera. As the Bureau uses International Business
Machines in its geodetic work, the application of computational analytical
aero-triangulation appears to be both possible and practical. Studies of analyti-
cal methods are in progress. Infrared photography has been tested in swamp
areas and found to be a valuable auxiliary water delineation source. Plans are
being followed steadily to replace as rapidly as practical all graphic compilation
with stereoscopic instrument compilation. The report of Mr. Harry [6] indi-
cates very high accuracies that are possible by means of photogrammetry. Ac-
curacies of this relative dimension would be useful for the hydrographic control
work of the Coast and Geodetic Survey. Although the use of signalized points
has not been seriously employed in the United States, it is considered that it
may present one method for greatly improving the accuracy of photogram-
metric control surveys for nautical chart compilation.
REFERENCES
[1] Harris, William D., “Stereoscopic Mapping with the U. S. Coast and Geodetic Survey Nine-
lens Camera," Archives Internationales de Photogrammetrie, Vol. XI, part 2, page 404, 1954.
[2] Tewinkel, G. C., “Adjustment of the Nine-lens Aerial Camera of the U. S. Coast and Geodetic
Survey," Archives Internationales de Photogrammetrie, Vol. XI, part 1, page 233, 1954.
[3] Jones, Bennett G., ‘Photogrammetric Surveys for Nautical Charts,” International Hydro-
graphic Review, Monaco, November, 1955.
[4] Brooks, H. R., “Use of Aerial Photographs for Revision of Land Information on Nautical
Charts,” International Hydrographic Review, Monaco, November, 1955.
[5] Tewinkel, G. C., “Stereotriangulation Adjustment,” Journal of the Coast and Geodetic Survey,
June, 1956.
[6] Harry, H., “La Situation Actuelle dans la Mensuration Cadastrale Photogrammetrique,”’
Photogrammetria, Vol. XI, n. 2, 1954-53.
