If you translate this in GIS terms, A and B are the origins of two different coordinate reference systems. So, for the same destination, you give different information in order to find your place. If they don't approach from the same side of the road, you will need to give different indications to each.įrom point A, you will tell your friend to drive 250 m then it will be on his right.įrom point B, you will tell your friend to drive 750 m then it will be on his left. The first thing that you need to know is from which direction they will approach your street. Imagine that you need to guide two friends who are trying to find your house. Let's take a one dimensionnal case as an exampple. Reprojection in GIS consists in changing the coordinates values of a dataset from one coordinate system to another coordinate system. What is actually happening when you Reproject the data from one projection, to another, projection. to reproject (warp) an existing lat/long project to a specific projection This GIS SE post is useful for that Understanding concept of Spatial Reference System?Īnd this answer with a link to a working manual of projections is a great resourceĪgain this Wikipedia page starts to touch on reprojection I understand the reality that the earth has an irregular shape and the that different reference systems 'tie' theoretical co-ordinates to real places on the planet surface, and that different CRS are needed around the globe. I understand Coordinate Reference Systems. The coordinates for data change depending on the datum and spheroid on which those coordinates are based, even if they are using the same map projection and parameters. The terms 'geographic coordinate system' and 'datum' are used interchangeably, but as noted above, a GCS includes a datum, spheroid, units of measure and a prime meridian. The ESRI FAQ about Projection Basics is good - From this. I have searched the web with "What is reprojection?" and I have had a good read. It comes up a lot in questions on Stack Exchange, and there are plenty of How to questions and answers about specific issues using various software. One thing that I can't quite get my head around is Reprojection.
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