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SHADING AND ENGRAVING TOPOGRAPHICAL PLANS.
AFTER all the mechanical portions of the survey, (including the horizontal contours if they have been traced instrumentally,) have been plotted to the required scale; the features of the ground, and any other detail that may have been sketched in the field, are transferred to the original plot for the commencement of the finished plan, supposing one to be required either to be preserved as a drawing, or for the purpose of engraving. This is generally finished with a brush, either in Indian ink or sepia; but a grea want of one general system of topographical plan-drawing is here felt, particularly as regards the method of expressing the features of the ground in a manner at once easy of execution and generally intelligible.
The different disposition of the light affords the means of varying the system of shading hills. Where it is supposed to descend in parallel vertical rays upon the ground, each slope evidently receives less light, or, relatively speaking, more shade, in proportion to its deviation from a horizontal plane, on which the maximum of light falls. Mr. Burr, in his "Practical Surveying," devotes a chapter to the scale of shade to be applied to plans finished on this supposition, which however he candidly acknowledges to be an impracticable theory; but it leads him to the very just conclusion, that hills are generally shaded much too dark to give anything like a natural representation of their various slopes, which defect has also the additional fault of confusing the appearance of the drawing, and impairing the accuracy of the outline. The slopes drawn upon this system have evidently no light or dark sides, which causes a monotonous effect; and yet, on the same plan, both trees and houses are constantly represented with shadows.
SHADING AND ENGRAVING TOPOGRAPHICAL PLANS.
The other system of supposing the light to fall obliquely upon the ground (as in nature), either at one fixed angle or at an angle proportioned to the general character of the slopes *, is decidedly favourable to the talent of an artist; but there are two objections its general adoption in plans of an extended survey: first, the difficulty of execution; and secondly, its ambiguity, even when correctly drawn, except to those accustomed to the style. The slopes directly opposed to the light would evidently receive a greater portion of illumination than the summits of the highest hills; and, in fact, the whole arrangement of the disposition of the shades is quite different from what it would be under a vertical light, as is seen by exposing a model of any portion of ground to a strong light from a partially-closed window. The practice of copying the effects of light and shade from models is the best introduction to this system of shading ground, and is in fact indispensable before attempting to finish a plan †.
The method now most generally practised in topographical plandrawing partakes of both these systems; the light is considered as falling nearly vertical, but sufficiently oblique to allow of a decided light and shade to the slopes of the hills, trees, &c. The hills are shaded, not as they would really appear in nature, but on the conventional system of making the slopes darker in proportion to their steepness; the summits of the highest ranges being left white. This arrangement, though obviously incorrect
* Mr. Burr proposes an angle of about 15° for a flat country, and 40° for mountainous districts; the angle of oblique light ranging between these two extremes according to the nature of the ground.
Mr. Dawson, whose talents and energy have done so much towards bringing the sketching and shading plans of the Ordnance Survey to the present state of perfection, was the principal advocate of this system of oblique light; and some of the copies, from models of large tracts of country drawn by Mr. Carrington, at the Ordnance Map-office, in the Tower, are hardly to be distinguished from the models themselves, when they are both placed in the proper light.
These and the preceding remarks apply solely to shading with the brush; the methods of delineating slopes by the pen and pencil having been explained in the last chapter. The Ordnance Surveys of the North of England are finished on this system for the engraver, even though the ground may have been instrumentally contoured. These maps, however, are at present engraved upon the same scale as those of the old surveys of the southern counties, 1 inch to 1 mile, though plotted upon that of 6 inches, in order to have the whole maps of England uniform in scale and in execution.
SHADING AND ENGRAVING TOPOGRAPHICAL PLANS. 117
in theory, has the advantage of being generally understood even by those not accustomed to plan-drawing, and is also easy of execution: it is that now adopted in finishing the plans of the Ordnance Survey, and from which the features of the ground are engraved on the vertical system of etching, as being much the easiest, although not so for sketching in the field.
Trials have also been made to render the patent process of engraving by a machine, known by the name of "Anaglyptograph," which answers so beautifully for giving a correct representation of a cast, or basso-relievo, available for topographical designs. A surprising relief is produced by this method of engraving, but it renders the general surface of the plan so dark as to obscure the accuracy of the outline; and as it is necessary that a model should be previously made of the feature to be represented, it is only suited to small portions of irregular ground.
Attempts have likewise been lately made to introduce some system of engraving that may combine as far as it is possible the accuracy of horizontal contours with the effect of etching, which it is hoped will before long be brought into practice.
In finishing detailed plans on a large scale, stone or other permanent buildings are generally coloured red (lake or carmine). Wooden or temporary structures are tinted with a shade of Indian ink. Water is always coloured blue. Where distinctions between public and private buildings or property are required to be shown, different colours must be used and explained by references on the drawing; the same remark applies to the distinction between buildings erected and those only contemplated. The most usual conventional signs have already been alluded to in pages 68 and 69.
Previous <unk>Continue <unk> SHADING na ENGRAVING Mipango ya Topographical. Baada ya sehemu zote za mashine za uchunguzi (ikiwa ni pamoja na contours usawa kama wamekuwa traced instrumentally) wamekuwa plotted kwa kiwango kinachohitajika, sifa ya ardhi, na maelezo yoyote ambayo inaweza kuwa sketched katika uwanja, ni kuhamishwa kwa njama ya awali kwa ajili ya kuanza ya mpango kumaliza, kudhani moja inahitajika ama kuhifadhiwa kama kuchora, au kwa madhumuni ya kuchonga. Hii ni kwa ujumla kumaliza na brush, ama katika wino Hindi au sepia; lakini kubwa haja ya moja ya mfumo wa jumla ya topographic mpango kuchora ni hapa waliona, hasa kuhusiana na mbinu ya kueleza sifa ya ardhi katika njia moja kwa moja rahisi ya utekelezaji na kwa ujumla intelligible. Mpangilio tofauti wa nuru hutoa njia ya kutofautisha mfumo wa milima ya kivuli. """Pamoja na kupungua kwa mteremko kwa mtiririko wa mviringo, kila mteremko hupokea mwanga mdogo, au kwa kusema kwa kiasi, kivuli zaidi, kulingana na kupotoka kwake kutoka kwa usawa wa usawa, ambapo mwanga mwingi huanguka." "Burr, katika ""Practical Surveying,"" anatoa sura kwa kiwango cha kivuli kutumika kwa mipango ya kumaliza juu ya dhana hii, ambayo hata hivyo yeye wazi anakiri kuwa nadharia impracticable, lakini inaongoza yake kwa hitimisho haki sana kwamba milima ni kwa ujumla shaded sana giza kutoa kitu kama uwakilishi wa asili ya mteremko wao mbalimbali, ambayo kasoro pia ina kosa la kuchanganyikiwa muonekano wa mchoro, na kuharibu usahihi wa muhtasari." Mteremko uliochorwa juu ya mfumo huu wazi hauna upande mwanga au giza, ambayo husababisha athari ya monotonous; na bado, kwenye mpango huo huo, miti na nyumba zote mbili zinawakilishwa daima na vivuli. Shading na engraving topographic mipango. Mfumo mwingine wa kudhani mwanga kuanguka obliquely juu ya ardhi (kama katika asili), ama katika pembe moja fasta au katika pembe inalingana na tabia ya jumla ya mteremko, ni dhahiri mazuri kwa vipaji ya msanii; lakini kuna pingamizi mbili kwa ajili ya matumizi yake ya jumla katika mipango ya uchunguzi wa muda mrefu: kwanza, ugumu wa utekelezaji, na pili, ambiguity yake, hata wakati sahihi kuchorwa, isipokuwa kwa wale kutumika kwa mtindo. Mteremko ulio kinyume kabisa na mwanga, kwa wazi, utapokea sehemu kubwa ya mwangaza kuliko vilele vya vilima vya juu; na kwa kweli, mpangilio mzima wa mpangilio wa vivuli ni tofauti kabisa na kile kitakachokuwa chini ya mwanga wa wima, kama inavyoonekana kwa kufunua mfano wa sehemu yoyote ya ardhi kwa mwanga mkali kutoka dirisha lililofungwa kwa sehemu. Mazoezi ya kunakili athari za mwanga na kivuli kutoka kwa mifano ni utangulizi bora kwa mfumo huu wa ardhi ya kivuli, na kwa kweli ni muhimu kabla ya kujaribu kumaliza mpango. Njia ya sasa zaidi kwa ujumla mazoezi katika topographic plandering kushiriki katika mifumo yote miwili; mwanga ni kuchukuliwa kama kuanguka karibu wima, lakini oblique kutosha kuruhusu ya kuamua mwanga na kivuli kwa mteremko wa milima, miti, na kadhalika. milima ni shaded, si kama wao kweli kuonekana katika asili, lakini juu ya mfumo wa kawaida ya kufanya mteremko giza zaidi kwa uwiano wa mwinuko wao. Mr. Burr anapendekeza pembe ya karibu 15 ° kwa nchi tambarare, na 40 ° kwa wilaya za milima; pembe ya mwanga wa mteremko unaoanzia kati ya pande hizi mbili kulingana na asili ya ardhi. Dawson, ambaye talanta na nishati yake wamefanya mengi sana kuleta michoro na shading mipango ya Ordnance Survey kwa hali ya sasa ya ukamilifu, alikuwa mtetezi mkuu wa mfumo huu wa mwangaza oblique, na baadhi ya nakala kutoka kwa mifano ya maeneo makubwa ya nchi iliyochorwa na Carrington katika Ordnance Map Office katika Tower ni vigumu kutofautisha kutoka mifano wenyewe, wakati wote wawili ni kuwekwa katika mwanga sahihi. Maelezo haya na yaliyotajwa hapo juu yanatumika tu kwa rangi ya brush; mbinu za kuelezea mteremko kwa kalamu na penseli zimeelezwa katika sura ya mwisho. Uchunguzi wa silaha za kaskazini mwa Uingereza umekamilika kwa mfumo huu kwa mchongaji, ingawa ardhi inaweza kuwa imefanywa kwa njia ya kifaa. Hata hivyo, ramani hizi kwa sasa zimechongwa kwa kiwango sawa na zile za uchunguzi wa zamani wa kaunti za kusini, inchi moja hadi maili moja, ingawa zimechorwa kwa inchi sita, ili kuwa na ramani nzima ya Uingereza sawa katika kiwango na utekelezaji. Shading na engraving topographic mipango. "117 ""Kupiga picha kwa njia ya mviringo ni rahisi zaidi, ingawa si rahisi kwa ajili ya kuchora picha za mashamba." "Kama ilivyoelezwa hapo juu, ""anaglyptography"" ni mbinu ya kuchonga kwa mashine, ambayo inatoa uwakilishi sahihi wa mchoro au bass-relief kwa ajili ya muundo wa topografia." Njia hii ya kuchonga hutokeza relief ya kushangaza, lakini inafanya uso wa jumla wa mpango kuwa giza sana ili kuficha usahihi wa muhtasari; na kama ni muhimu kwamba mfano unapaswa kufanywa hapo awali wa kipengele cha kuwakilishwa, ni sahihi tu kwa sehemu ndogo za ardhi isiyo ya kawaida. Vivyo hivyo, majaribio yamefanywa hivi karibuni kuanzisha mfumo fulani wa kuchonga ambao unaweza kuchanganya kadiri iwezekanavyo usahihi wa mviringo wa usawa na athari ya kuchonga, ambayo inatarajiwa kutolewa katika mazoezi. Katika kumaliza mipango ya kina kwa kiwango kikubwa, mawe au majengo mengine ya kudumu kwa ujumla ni rangi nyekundu (ziwa au carmine). Miundo ya mbao au ya muda hupakwa rangi ya wino wa Kihindi. Maji huwa na rangi ya bluu sikuzote. Wakati tofauti kati ya majengo ya umma na binafsi au mali zinahitajika kuonyeshwa, rangi tofauti lazima zitumiwe na kuelezwa kwa marejeo kwenye mchoro; maelezo sawa yanatumika kwa tofauti kati ya majengo yaliyojengwa na yale yaliyopangwa tu. Mifano ya kawaida ya kawaida imetajwa katika ukurasa wa 68 na 69.