extract point data or line profile over the displayed tif about geotiff.js HOT 7 CLOSED

Hi @mattijn

unfortunately this functionality is not (yet) part of the geotiff library, but (fortunately) can be solved outside of it.

Here are some thoughts regarding point or line sampling.

First off, you have to consider interpolation when you are dealing with sub-pixel coordinates. The easiest way would be to round to the nearest integer which would result in a nearest neighbor "interpolation" (not really interpolating), which is fine for some applications but not for all. Another fairly easy option would be bilinear interpolation, where you get the nearest 4 pixels and then linearly interpolate.

When you are not reading the full image into one array, but a subset, then you have to take the offset of the subset window to the full image into consideration as-well.

Also you have to choose whether you want to sample the original data, or the plotty-rendered RGB.

Does this help you?
Do you think point or line sampling would be a good addition to geotiff.js functions?

from geotiff.js.

Currently I plot a raster on a leaflet map using geotiff.js and plotty.js. This works great. No need for geoserver or mapserver. I think thats a big plus.

Next step for me is to interact with the raster once a user clicks somewhere on raster in the map, For point sampling I now use gdallocationinfo to get the specific point in the raster by querying the tif (in lat/lon) on the server-side.
With a dedicated function I could make this to work as well for line sampling, but I haven't done it yet.

But, thats all server-side, while I got my raster loaded in my clients browser through geotiff.js. You mention that you can choose to sample the original data or the RGB, I didn't realize that is possible. For me I would think to sample the original data as I otherwise have to translate the RGB values to numbers, isn't it?

Your thoughts definitely helps! For me, I think it would be a great to be able to do point or line sampling on the client side, while I'm not sure if it should be included in geotiff.js, as it is not so much an tif encoding issue. Might be a potential side library?

from geotiff.js.

Currently, the "geo" part of geotiff.js is somewhat neglected. Sure, the geo-keys are read and decoded, but not used any further. I think it would be beneficial to interpret them to allow a translation of geo-coordinates (eg: lat-lon) to pixel coordinates. The main issue here is that there are a lot of possibilities to encode the geo referencing within the geotiff (tie-points, custom CRS definitions, ... you name it).

I think I could implement a function to allow pixel lookups for images with simple affine transformations and include it in geotiff.js. I'm not sure when I will be able to do so, though.

But, thats all server-side, while I got my raster loaded in my clients browser through geotiff.js. You mention that you can choose to sample the original data or the RGB, I didn't realize that is possible. For me I would think to sample the original data as I otherwise have to translate the RGB values to numbers, isn't it?

Well, the array you read using readRaster is the "raw" data, which is passed to plotty to generate the RGB version. So, if you have a simple case (e.g: where the image CRS is equal to your leaflet map CRS for example) you could quite easily transform the coordinates to pixel space and then query this retrieved array and get your real pixel value.

from geotiff.js.

Hi there @mattijn @constantinius

I'm currently developing a Leaflet plugin that might be interesting for this use case. It uses geotiff.js, but also reads ASCII Grid files, and allows onclick to identify values.

Have a look at it : https://github.com/IHCantabria/Leaflet.CanvasLayer.Field
And here there are some examples: https://ihcantabria.github.io/Leaflet.CanvasLayer.Field/

It is a work in progress, so any feedback is welcome!

from geotiff.js.

@VictorVelarde: This looks really nice, and is a good example how to query raster values at a given coordinate. Nice job with the animated layers, they look gorgeous!

from geotiff.js.

Thanks @constantinius
Your library has been an important boost for it!

from geotiff.js.

Hi!, this issue should be probably closed!

from geotiff.js.