Title: Hourglass: an unpublished map projection by John P. Snyder Show Chinese title

Title: 霍尔特萨：约翰·P·辛德比未发表的投影方法

Abstract: Hourglass is an equal-area pseudocylindrical map projection developed by John P. Snyder in mid 1940s. It was never published in a detailed way by its author, and only a couple of references exist in literature since 1991, both of them including a picture but without any mathematical description. In this work the equations for the ellipsoid and for the sphere are derived, both for direct and inverse problems, together with a generalization that allow meridians not restricted to straight lines as in the original Snyder's version. Although not useful for world maps, the projection can be employed for mapping areas around their standard parallels. Show Chinese abstract

Abstract: 霍尔莫塞是约翰·P·辛格在20世纪40年代中期开发的一种等面积伪圆柱投影。 作者从未以详细的方式发表过该投影，自1991年以来的文献中仅有少数几篇参考文献，其中都包含一张图片但没有任何数学描述。 在本工作中，推导了椭球和球体的方程，包括正算和反算问题，同时还进行了推广，使得经线不限于辛格原始版本中的直线。 尽管对于世界地图不实用，但该投影可以用于绘制其标准纬线附近的区域。