Example: Change Projection of an Image

In this example we use the Change Coordinate System command to change the projection of an image from Latitude / Longitude to a custom Orthographic coordinate system centered on Florida.  The image shows raster data showing terrain elevations in a region of Florida.




We start with the raster data opened in an image window, as seen above.   The data was imported from a format that correctly specified Latitude / Longitude with WGS 84 base as the projection.    We will re-project the data into Orthographic projection centered up Florida.




With the focus on the opened Florida image, in the Contents pane click the coordinate system picker button for the Florida layer and click Change Coordinate System.




In the Change Coordinate System dialog we click the coordinate system picker button and then we choose Edit Coordinate System to choose a new coordinate system.




If we have favorites assigned we could click on the star button to choose from those.  Manifold uses the terms coordinate system and projection interchangeably as synonyms.  



Orthographic projection is readily available in the staggeringly long list (good to have a  filter box to reduce it down to only those entries of interest...) of coordinate system Manifold knows, literally thousands of them.    But we want not just Orthographic but Orthographic centered upon a particular latitude and longitude that is approximately the center of Florida.   That is a Custom projection so we will click the Custom tab.




Orthographic is found in the list of coordinate systems in the Type box.



We pull down the list and choose Orthographic.



We enter 29 for the Center latitude and -82 for the Center longitude.    The location at 29 degrees North and 82 degrees West is close enough to the center of Florida for our purposes.  We can get that number by hovering the mouse cursor over the center of Florida on any map or display in Manifold and noting the location in the status bar or by asking Google or Bing online.  Orthographic projects the entire hemisphere of the Earth so any center value anywhere near Florida is good enough to provide a nice display of what we would see if we were hovering above the state on the edge of space and looking down at Florida.  


If this was a coordinate system we would use regularly we would probably change the Name to something more self-documenting than "Custom Coordinate System,", such as Orthographic Centered on FL.   But to emphasize what we created was a custom system in this example we will leave the default Name as is.   We press OK.




That closes the Coordinate System sub-dialog and puts us back in the Change Coordinate System dialog where now we see a Custom Coordinate System has been chosen.


Reprojecting an image means changing the dimensions and numbers of pixels so the only option is to Add Component, that is, to create a new image and table in the Project that are a copy of the subject image, but re-projected into the new coordinate system.   See the Re-Projection Creates a New Image topic for why re-projecting an image changes the number of pixels.




The result is that a new image, called Florida 2 is created in the Project along with a new table, Florida Table 2, that stores the tiles for the new image.




If we click open the new image we see it is as yet not styled.  That's easy to fix.  We could either open the Style panel and style the image, or we can simply copy and paste the styling from the original Florida image into the new Florida 2 image in the mfd_meta table.  


We can do that using the procedures shown in the Example: Style Properties in the mfd_meta Table  topic to copy the value of the StylePixel property from the Florida StylePixel record to the Florida 2 StylePixel record in the mfd_meta table.




There... that's better!




Image Size - When changing the projection of images Manifold will choose a new size for the re-projected image that approximates the size of the original while providing enough room for necessary pixel interpolations.   See the discussion in the Re-Projection Creates a New Image topic.


About that Copy and Pasting of Style - The workflow above mentions using copy and paste to transfer Style from the Florida image to the new Florida 2.  How did we do that?   Experienced Manifold operators will often just copy and paste the StylePixel value from one image to another in the mfd_meta table, as illustrated in the Style: Palettes  topic's discussion of the StylePixel Property.



In this particular example we opened the mfd_meta table, and copied the value of the StylePIxel property for Florida.   Since Florida 2 was as yet totally unstyled it had no StylePixel property.  We could have applied a simple style and then copied and pasted the StylePixel value, but instead it was quicker to just add a new row, the last row seen above with a Name of Florida 2, a Property of StylePixel and then pasting the value we previously copied.  Like magic, the image immediately updates to use the new Style.


See the Example: Style Properties in the mfd_meta Table  topic for an analogous example using drawings.


That is only part of Florida - The image called Florida might seem to be the entire state, but it is just an accident of terrain that the long feature is similar to the shape of the Florida peninsula.   If we create a new data source that is an imageserver and then show the Florida terrain image overlaid as a layer in a map with Bing, we see that it shows a region in central Florida.




The light gray feature branching from the lower left corner towards the center is the depression of the Peace River drainage basin, extending to the Northeast from Port Charlotte and Punta Gorda.    The brighter colors show slightly elevated terrain that forms a low ridge to the Northwest of Lake Okeechobee.


See Also



Assign Initial Coordinate System


Change Coordinate System


Map Projection


Favorite Coordinate Systems


Favorite Base Coordinate Systems


Example: Adding a Favorite Coordinate System - Step by step example showing how to add a frequently used coordinate system to the Favorites system.


Example: Style Properties in the mfd_meta Table


Re-Projection Creates a New Image - Why changing the projection of an image creates a new image.


About Coordinate Systems


Projections Tutorial