TWD97、WGS84：基準？投影？

TWD97 and WGS84, Datum or Map Projection?

「TWD97」與「WGS84」，分別是台灣測量製圖與美國GPS所使用的「大地基準」。但是在近十餘年間，台灣空間資訊領域，在從業人員交談中、論文發表中、甚至部分官方網際服務系統的選單中，常見以「WGS84」為經緯度的代稱，而以「TWD97」為投影坐標之同義詞。本文藉由概要說明「TWD97」與「WGS84」之真實含意，探討此一現象之發生，以釐清「由WGS84轉換為TWD97坐標」之作為。並期望能為此一名詞的混淆，提供一項澄清。

TWD97 and WGS84 are two geodetic datum used by Taiwan and the United States GPS satellite navigation system, respectively. However, recently, WGS84 has been an equivalent term for geographic coordinate system (latitude-longitude), and TWD97 is another way of expressing projected coordinates in Taiwan. This phenomenon is observed in discussions by professionals in the geomatics field, in published papers, and also found in the coordinate system selection options for government websites. This paper briefly introduces the meaning of TWD97 and WGS84 respectively and explores the origin of this phenomenon. The content of “converting from WGS84 to TWD97” is also discussed for clarification.