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| 0747 |
Southern Tibet : vol.4 |
Citation Information
OCR Text
427
An examination carried out by Colonel Byström proves, however, that there is a length-
error of 109.5 km. or 2.56% of the route (4,270 km.), and a cross-error of 1.52%.
In his critical examination quoted above Professor Rosén has examined 21 different
sections of routes from my journey in 1899—1902. He has subdivided them into
two groups, the first of which, Nr. 1—10, are routes chiefly stretching from east
to west and thus situated in latitudinal valleys. He says: »Here the length-error is
as an average 2% of the route. Such an exactitude is regarded as good when
stepping the distance on even ground (Vide: Jordan, Handbuch der Vermessungs-
kunde, 1908, II, p. 85).» Professor Rosén regards the result of the first group
as very good. The second group, Nr. 11—21, chiefly consists in meridional routes
crossing passes and difficult ground. Here the length-error is 4—5%, which Rosén
regards as quite satisfactory. In the first group the cross-error was found to be
approximately 2% or the same as the length-error.
The polygon mentioned above is partly meridional, crossing passes, partly
running east-west through latitudinal valleys. As could be expected, the length-
error therefore will be more than 2% and less than 4—5%, and indeed it was found
to be 2.56%.
The polygonal route I travelled in 1900 through North-eastern Tibet from
Temirlik to the south, west, north and finally back eastwards to Temirlik was
1,656 km. in length. The endpoint fell 31 km. east of the starting point, being thus
with an error of 1.81%; and 9 km. north of it, being 0.54%.
In 1900 and 1901 I accomplished another polygon, starting from Altmish-
bulak and going S. S. W. through the desert of Lop, further S. E. and E. N. E.
through the mountains of Astin-tagh and Akato-tagh to Anambaruin-ula, thence
northward through the desert to Kuruk-tagh and westwards back to Altmish-bulak.
This polygon is 1,460 km. in length, the length-error 0.20% and the cross-error
practically 0%, as I reached the very spring in the middle of the desert and in very
foggy weather, without assistance of astronomical observations. In this case the
ground was very favourable and comfortable. From the dates given above we find
the law, so natural in itself: the error increases in the same proportion as the ground
becomes worse. The most difficult routes of all are the meridional ones through
Tibet during the summer when the ground is soft. The easiest and nearly level
regions are to be found in those parts of the Central-asiatic deserts where there is
no sand, and here the winter is the best season. Thus we find:
Length-error. Cross-error.
Meridional routes in Tibet during the summer . . . 4—5%
Meridional and latitudinal routes in Tibet all directions
and all seasons . . . . . . . . . . . . . 2.56% 1.52%
Latitudinal valleys in Tibet all seasons . . . . . . about 2% about 2%
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746
747
748
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