tag:blogger.com,1999:blog-8852543472291091913.post3744786566453437785..comments2017-03-31T01:58:09.160-06:00Comments on Software Everything: Building a Custom 2D Map Component from Scratch using Virtual EarthJohn Valentinohttps://plus.google.com/111160268055349481644noreply@blogger.comBlogger10125tag:blogger.com,1999:blog-8852543472291091913.post-2784416745156801672011-05-05T01:46:52.139-06:002011-05-05T01:46:52.139-06:00John.
i have another question about the distance ...John.<br /><br />i have another question about the distance calculation (meters/pixel).<br />as i understood, the meter per pixel value is reduce once you go up and down from the equator, so let's say i have a building (for instance) with 20 meters * 20 meters dimensions, if the building located on the equator (latitude 0) it's should looks realistic but if it's located on lower or higher latitude it'll distort since the meters per pixel there is smaller. <br />For example, if 20m on the equator are taken 20 pixels (again, for instance) on top or bottom of the world you should represent 20m with higher amount of pixels, am i right?שלומי ששוןhttp://www.blogger.com/profile/09475921385050758435noreply@blogger.comtag:blogger.com,1999:blog-8852543472291091913.post-73532006484935580732011-04-07T00:50:03.190-06:002011-04-07T00:50:03.190-06:00"... According to the "General Formulas ..."... According to the "General Formulas and Notations .."<br /><br />so the O(x,y) is accumulate all of the drags that occur from the first time you loaded the map system?<br /><br />"... he offset from the center tile image in the local coordinate system..."<br /><br />but when you drag, the 'locally center tile' is changed all the time and not stay the same like 1st one that was on the system loading, for instance, let's say that on the system loading the 'locally center tile' was (3,3) and you dragged the map to another position that now the 'locally center tile' is (6,6), what will be the O(x,y) value (approximated)? the accumulation of all the way till (6,6) or you zeroing it sometimes?<br /><br />thanks.<br /><br />Shlomi.Shlomihttp://www.blogger.com/profile/09475921385050758435noreply@blogger.comtag:blogger.com,1999:blog-8852543472291091913.post-69296206929490220272011-04-06T19:41:43.949-06:002011-04-06T19:41:43.949-06:00According to the "General Formulas and Notati...According to the "General Formulas and Notations," O (x, y) is used to represent the offset from the center tile image in the local coordinate system. This position is 0,0 until the map is moved. Since this is the local coordinate system once the map is moved, say 10 pixels fo the right, that would make the offset -10, 0.<br /><br />This is just one of many ways to place tiles and calculate how to move them. Using matrices would be the preferred mechanism; I just found relative geometry a bit more approachable for most people.John Valentinohttp://www.blogger.com/profile/15025531615679576013noreply@blogger.comtag:blogger.com,1999:blog-8852543472291091913.post-80511188921401405022011-04-06T19:31:55.044-06:002011-04-06T19:31:55.044-06:001. why it's like that, mean, why the latitudes...1. why it's like that, mean, why the latitudes are decreased when you going north and south from the equator?<br /><br />This is because a 3D spherical space was projected into a 2D rectangular space, which means that compression had to occur somewhere. For more information see read this article on "Map Projection": http://en.wikipedia.org/wiki/Map_projection<br /><br />2. why the world is a square and not oblong, from my prior understanding, the world height should be half then it's width to the whole world should be oblong.<br /><br />This is how a tile system like Virtual Earth or Google Maps works. Why? Historically it was easier for people to store physical 2D maps on paper rather than as a series of 3D globes. As for why not 2D oblong, see the WIki page on "Map Projection."John Valentinohttp://www.blogger.com/profile/15025531615679576013noreply@blogger.comtag:blogger.com,1999:blog-8852543472291091913.post-85408758208942067442011-04-06T19:19:08.150-06:002011-04-06T19:19:08.150-06:00Yes, this is the reason for the clipping of the wo...Yes, this is the reason for the clipping of the world's height. Those locations do exist at the north and south poles; you just can't view them accurately on a tile based 2D system.John Valentinohttp://www.blogger.com/profile/15025531615679576013noreply@blogger.comtag:blogger.com,1999:blog-8852543472291091913.post-8657666203594892972011-04-06T02:33:08.264-06:002011-04-06T02:33:08.264-06:00Hi again,
i have another question:
for the calcu...Hi again, <br /><br />i have another question:<br />for the calculation of "Positioning tiles relative to center", you're using O(x,y), what's you meant by: ".. which is (0,0) until a pan"?<br />it's for tiles that not nearby the local center image?<br /><br />TA.<br /><br />ShlomiShlomihttp://www.blogger.com/profile/09475921385050758435noreply@blogger.comtag:blogger.com,1999:blog-8852543472291091913.post-6196403266823152462011-04-05T00:59:02.501-06:002011-04-05T00:59:02.501-06:00OK.
now, if it's ok, i have another 2 questio...OK. <br />now, if it's ok, i have another 2 questions:<br />1. why it's like that, mean, why the latitudes are decreased when you going north and south from the equator?<br />2. why the world is a square and not oblong, from my prior understanding, the world height should be half then it's width to the whole world should be oblong.<br /><br />my system already consider the world as oblong, is this mandatory to consider it's as a square?Shlomihttp://www.blogger.com/profile/09475921385050758435noreply@blogger.comtag:blogger.com,1999:blog-8852543472291091913.post-57141872913064264842011-04-04T00:41:43.998-06:002011-04-04T00:41:43.998-06:00Ok.. now it's more clearly and i assume this i...Ok.. now it's more clearly and i assume this is the reason that the world's height i between 85.X to -85.X degrees but whats happened between this and 90 on north (or -90 on south)? i mean, the coordinates (geo) [90, 180] or [-90, 180] or [90, -180] or [-90, -180] are exists somewhere?Shlomihttp://www.blogger.com/profile/09475921385050758435noreply@blogger.comtag:blogger.com,1999:blog-8852543472291091913.post-63113589015610248272011-04-03T10:07:54.027-06:002011-04-03T10:07:54.027-06:00In the first picture in this article the world map...In the first picture in this article the world map is divided into squares with their mappings to the lat-lon, row-column, and x-y systems. Notice how all of the squares are the same size in terms of pixels (256 by 256). Then notice that the degrees of longitude (the widths) of each square is 45 degrees, but that the degrees of latitude (the heights) are not evenly spaced. For example the square at 0,3 is 40.98 degrees in height and 256 pixels in height, while the square at 0,2 is 25.53 degrees in height and 256 pixels in height.<br /><br />The "Latitude and longitude to row by column" and "World x and y to latitude and longitude" equations are used to convert between longitude-latitude, row-column, and x-y. These equations take into account that degrees of latitude are not evenly spaced.John Valentinohttp://www.blogger.com/profile/15025531615679576013noreply@blogger.comtag:blogger.com,1999:blog-8852543472291091913.post-30849374939749798602011-04-03T07:50:03.404-06:002011-04-03T07:50:03.404-06:00hi.
thanks for wonderful article, i just have que...hi.<br /><br />thanks for wonderful article, i just have question, can you please explain more this paragraph:<br />"<br />Due to the way the earth in compressed in a tiled map, the lines of latitude are now evenly spaced even through they are the same pixel distance apart. This requires a formula to be used to determining latitude that takes into account this difference.<br />"<br /><br />thanks.<br /><br />ShlomiShlomihttp://www.blogger.com/profile/09475921385050758435noreply@blogger.com