Eliminate grey space around the saved map

Question

I have mapped my Gazebo environment using the slam_gmapping node. On running map_server map_saver -f map_1.pgm, I am able to save the map to my local disk.

This is how the saved map looks -

As we can see, there is a lot of grey space arond the map. How do I eliminate this? I need to do this because I intend to run some OpenCV algorithms over this map.

This is my map_1.yaml looks like -

image: map_1.pgm
resolution: 0.050000
origin: [-100.000000, -100.000000, 0.000000]
negate: 0
occupied_thresh: 0.65
free_thresh: 0.196

Answer 1

Maybe you are looking to crop the occupancy grid. Map server provides some api's for cropping. This sample script from their documentation would shed some light

#!/usr/bin/env python

import sys
import yaml
from PIL import Image
import math

def find_bounds(map_image):
    x_min = map_image.size[0]
    x_end = 0
    y_min = map_image.size[1]
    y_end = 0
    pix = map_image.load()
    for x in range(map_image.size[0]):
        for y in range(map_image.size[1]):
            val = pix[x, y]
            if val != 205:  # not unknown
                x_min = min(x, x_min)
                x_end = max(x, x_end)
                y_min = min(y, y_min)
                y_end = max(y, y_end)
    return x_min, x_end, y_min, y_end

def computed_cropped_origin(map_image, bounds, resolution, origin):
00025     """ Compute the image for the cropped map when map_image is cropped by bounds and had origin  """
    ox = origin[0]
    oy = origin[1]
    oth = origin[2]

    # First figure out the delta we have to translate from the lower left corner (which is the origin)
    # in the image system
    dx = bounds[0] * resolution
    dy = (map_image.size[1] - bounds[3]) * resolution

    # Next rotate this by the theta and add to the old origin

    new_ox = ox + dx * math.cos(oth) - dy * math.sin(oth)
    new_oy = oy + dx * math.sin(oth) + dy * math.cos(oth)

    return [new_ox, new_oy, oth]

if __name__ == "__main__":
    if len(sys.argv) < 2:
        print >> sys.stderr, "Usage: %s map.yaml [cropped.yaml]" % sys.argv[0]
        sys.exit(1)

    with open(sys.argv[1]) as f:
        map_data = yaml.safe_load(f)

    if len(sys.argv) > 2:
        crop_name = sys.argv[2]
        if crop_name.endswith(".yaml"):
            crop_name = crop_name[:-5]
        crop_yaml = crop_name + ".yaml"
        crop_image = crop_name + ".pgm"
    else:
        crop_yaml = "cropped.yaml"
        crop_image = "cropped.pgm"

    map_image_file = map_data["image"]
    resolution = map_data["resolution"]
    origin = map_data["origin"]

    map_image = Image.open(map_image_file)

    bounds = find_bounds(map_image)

    # left, upper, right, lower
    cropped_image = map_image.crop((bounds[0], bounds[2], bounds[1] + 1, bounds[3] + 1))

    cropped_image.save(crop_image)
    map_data["image"] = crop_image
    map_data["origin"] = computed_cropped_origin(map_image, bounds, resolution, origin)
    with open(crop_yaml, "w") as f:
        yaml.dump(map_data, f)