Rendering a shapefile with a custom projection in GeoTools

Question

I have an image, a shapefile, and a method which can translate an x/y pixel location from the image into a latitude/longitude point or vice versa. I'm trying to use Geotools to render the shapefile on the image, but I can't seem to get it to work.

All of the examples and tutorials I can find use factories to retrieve pre-existing transforms and mappings, but how can I use my custom projection?

Edit: The image is the view from a satellite, which means that it cannot see the entire earth. Is Geotools capable of handling this?

Edit2: I don't think that this can be done easily in GeoTools, I ended up just writing what I needed from scratch.

Answer 1

I don't understand completely your question, probably due to my limit knowledge about projections, but you can read and transform the features of a shapefile easily: http://docs.geotools.org/stable/userguide/tutorial/geometry/geometrycrs.html#export-reprojected-shapefile

=== UPDATED ===

Here you can find a simple creating a CRS from a WKT expression: docs.geotools.org/latest/userguide/library/referencing/crs.html and docs.geotools.org/latest/userguide/library/main/geometry.html.

That can help you.

Answer 2

If it's a non-affine transformation, then you're going to have trouble with line segments staying straight when they should be curved in the image's space. This is a general problem with transforming vectors, and with sufficiently small line segments, isn't usually too much of a problem.

If you don't know ahead of time what the projection parameters are for the image, or if they cannot be represented by standard map-projection parameters - if the image hasn't been rectified for instance - then you really have one course open to you: manual rasterization. If you're on 3D-accelerated hardware, it would be a fairly simple fragment shader to map from one space to another, given that you have the function already. However, if you're working on a headless server or similar, you'll need to roll your own polygon rasterizer, transforming points from one space to the other as you go. This isn't too difficult, and much has been written on it in the past, but it is mostly just time-consuming to write.

A simple, if not very efficient, method would be to scan over each pixel in the satellite image, transform the coordinate into your polygons' space, and do a simple inside/outside test of that point on your polygons. If it's inside, then colour your pixel appropriately. Lines are a bit harder with this method, but you essentially have to measre the cross-track error of your point against the line, and colour it if it is within some distance, but this won't be very pretty. You could use an alpha value based on the CTE, which would smooth the lines out somewhat, but it's hardly the cutting edge of anti-aliasing.

Answer 3

Although this not exactly for Geotools, this should work.(actually this is for GeoServer). This explains how to define a custom projection, edit the EPSG.sql file, which is used to create the cached EPSG database.:

Manually editing the CRS database

Another option is creating your own PROJ4 expression for your custom projection. You can use http://spatialreference.org/ for this.