![]() ![]() (Image credit: ESA) Breakthrough in parallax measurements and galaxy mappingĪ real breakthrough in parallax measurement and therefore in determining distances of stars in our galaxy, the Milky Way, came with a mission called Hipparchos, after the ancient Greek astronomer that first used the method to estimate the distance of the moon. Because stars also move in space on their own trajectories, these circles actually turn into a spiral. The parallax effect causes the stars to seemingly perform tiny circles in the sky every year. "Today, with advanced technologies such as adaptive optics and interferometry, we can reach accuracies of a few dozen micro-arcsecond on large ground-based telescopes," Jos de Bruijne, an astronomer at the European Space Agency (ESA) said in a statement. But the flickering effect caused by Earth's atmosphere and the distortion of the telescope observations caused by Earth's gravity prevented astronomers from reaching a precision better than about 0.01 arcseconds (one arcsecond is an angular measurement equal to 1/3600 of a degree). His catalogue was extended to about 6,000 stars by Louise Freeland Jenkins in 1952, and to over 8,000 stars by William van Altena in 1995. In 1924, American astronomer Frank Schlesinger published a catalogue with the parallaxes of almost 2,000 stars, probing stellar distances out to a few dozen light-years from Earth. Over the following decades, astronomers, aided by the improvements in telescope technology gradually grew the catalogs of stellar distances using the parallax method. By the early 20th century, the list of stars with measured parallaxes grew to a few hundred, mostly thanks to the work of Dutch astronomer Jacobus Kapteyn. In the late 1830s, Bessel’s contemporaries and rivals Wilhelm Struve and Thomas Henderson provided one parallax measurement each, bringing the total number to three. This was the beginning of the long and tedious process of building a three-dimensional map of the universe. Based on his observations, Bessel calculated that the star 61 Cygni, one of the stars in the Cygnus constellation, must be about 10 light-years away from Earth. The first person to succeed at measuring the distance to a star using the parallax method was German astronomer Friedrich Bessel in 1838. Cassini subsequently used those measurements to compute the parallax determining Mars' distance from Earth. In 1672, Italian astronomer Giovanni Cassini and his colleague Jean Richer made simultaneous observations of Mars, with Cassini in Paris and Richer in French Guiana. The ancient Greek astronomer Hipparchus reportedly used observations of a solar eclipse from two different locations to calculate the distance of Earth's celestial companion. The first known astronomical measurement using parallax didn't involve a star but the moon. V_uv = vec2(a_uv.x * u_offset_layers_x, a_uv.The history of parallax measurements in astronomy Gl_Position = u_matrix * vec4(a_position, 1.0) In case, the following are the relevant excerpts from my vertex and fragment shader code (with irrelevant parts removed - using precision highp float): // vertex shader Is there a way of performing the calculations to guarantee that the texture sections loop perfectly? -perhaps using fract and floor in some unusual way? (I found this discussion but couldn't understand it fully because neither the OP nor the accepted answer explained the meaning of many of the variables: parallax offsets with texture atlas? It makes use of fract and floor, but this method might be incompatible. Also, the issue might not necessarily be a result of floating point inaccuracy alone. I have tried many things to do error corrections including multiplying by 1000.0 before performing mods and then dividing, clamping to specific ranges, and so on, but I haven't found a consistent solution. In the image above, it looks like my algorithm is sampling the space either to the left or right of the correct texture position, so it hits a transparent color, which is wrong. Again, the offset is 1.0 / (number of layers), or 0.2 here. (See the tear in the middle wall that reveals the castle and ocean behind it.)Īt each fragment, calculate the position in the texture at offset * i If the color is transparency, move to offset * (i + 1), etc. It works almost perfectly, but at certain offsets seams at the loop points are visible. I use the following (offset is 1.0 / number of layers, so 0.2): ![]() I am implementing 2d parallax scrolling in openGL using a single quad and a texture atlas. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |