lcmap.commons.tile
differenceclj
(difference point interval)Calculate difference between a point and 'prior' point on an interval.
The value of this function can be used to answer the question, what do I subtract from a point to find the point of the nearest tile that contains it?
Geospatial raster data geometry can be somewhat counter-inuitive because coordinates and pixel geometry are expressed with both positive and negative values.
Along the x-axis, pixel size (and thus the interval) is a positive number (e.g. 30 * 100). Along the y-axis though, the pixel size and interval is a negative value. Even though this may seem peculiar, using a negative value helps us avoid special cases for finding the nearest tile-point.
Parameters:
- point - a scalar value on the real number line
- interval - a scalar value describing regularly spaced points on the real number line
Calculate difference between a point and 'prior' point on an interval.
The value of this function can be used to answer the question,
what do I subtract from a point to find the point of the nearest
tile that contains it?
Geospatial raster data geometry can be somewhat counter-inuitive
because coordinates and pixel geometry are expressed with both
positive and negative values.
Along the x-axis, pixel size (and thus the interval) is a positive
number (e.g. 30 * 100). Along the y-axis though, the pixel size and
interval is a _negative_ value. Even though this may seem peculiar,
using a negative value helps us avoid special cases for finding the
nearest tile-point.
Parameters:
* point - a scalar value on the real number line
* interval - a scalar value describing regularly spaced points
on the real number linenearclj
(near point interval offset)Find nearest point given an interval and offset.
The nearest point will be lesser than the point for a positive interval, and greater than the point for a negative interval as is required when finding an 'upper-left' point on a cartesian plane.
This function is used to calculate the nearest points along the x- and y- axis.
Parameters:
- point - a scalar value on the real number line
- interval - a scalar value describing regularly spaced points on the real number line
- offset - a scalar value used to shift point before and after finding the 'preceding' interval.
Find nearest point given an interval and offset.
The nearest point will be lesser than the point for a positive
interval, and greater than the point for a negative interval as
is required when finding an 'upper-left' point on a cartesian
plane.
This function is used to calculate the nearest points along the
x- and y- axis.
Parameters:
* point - a scalar value on the real number line
* interval - a scalar value describing regularly spaced points
on the real number line
* offset - a scalar value used to shift point before and after
finding the 'preceding' interval.point->tileclj
(point->tile {x :x y :y :as point}
{:keys [x-interval y-interval x-offset y-offset] :as tile-spec})Find the nearest containing tile's point.
The resulting x value will be less than or equal to the input
while the resulting y value will be greater than or equal.
For this function to work properly, intervals and offsets must be expressed in terms of projection coordinate system 'easting' and 'northing' units.
Along the x-axis, this works as expected. The interval is a multiple of pixel size and tile size (e.g. 30 * 100 = 3000). Along the y-axis the interval is negative because the pixel size is negative, as you move from the origin of a raster file, the y-axis value decreases.
The offset value is used for grids that are not aligned with the origin of the projection coordinate system.
- point - a map containing :x and :y coordinates
- tile-spec - a map containing the interval and offset for x- and y-axis
Find the nearest containing tile's point.
The resulting `x` value will be less than or equal to the input
while the resulting `y` value will be greater than or equal.
For this function to work properly, intervals and offsets must be
expressed in terms of projection coordinate system 'easting' and
'northing' units.
Along the x-axis, this works as expected. The interval is a multiple
of pixel size and tile size (e.g. 30 * 100 = 3000). Along the y-axis
the interval is negative because the pixel size is negative, as you
move from the origin of a raster file, the y-axis value _decreases_.
The offset value is used for grids that are not aligned with the
origin of the projection coordinate system.
* point - a map containing :x and :y coordinates
* tile-spec - a map containing the interval and offset for x-
and y-axissnapclj
(snap x y tile-spec)Transform an arbitrary projection system coordinate (x,y) into the coordinate of the tile that contains it.
This function only works when working with points on a cartesian plane, it cannot be used with other coordinate systems.
- x - x coordinate
- y - y coordinate
- tile-spec - parameters for a tile's grid system
Transform an arbitrary projection system coordinate (x,y) into the coordinate of the tile that contains it. This function only works when working with points on a cartesian plane, it cannot be used with other coordinate systems. * x - x coordinate * y - y coordinate * tile-spec - parameters for a tile's grid system
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