Why scaleruler and northarrow functions cannot be used in mapshow figures

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Songqiu 2022-11-12

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评论： Songqiu 2022-11-21

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Hello everyone,

I just want to simply show scalebar and northarrow on my maps using the scaleruler and northarrow functions.

I tried the official help codes of MATLAB R2022a on mapshow as follows:

figure
mapshow boston.tif
S = shaperead('boston_roads.shp');
surveyFeetPerMeter = unitsratio('sf','meter');
x = surveyFeetPerMeter * [S.X];
y = surveyFeetPerMeter * [S.Y];
mapshow(x,y)
scaleruler on
northarrow

Then, I got the following errors:

Could you please tell me why and how to use scaleruler and northarrow on a mapshow figure?

Thanks a lot.

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Answer 1

Walter Roberson 2022-11-12

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When there is no existing axes then mapshow creates a standard numeric axes. mapshow is for displaying maps without projection, which is done on standard axes.

If, however, the existing axes is a mapping axes then mapshow can draw on it, but you need to avoid changing the map properties.

So you could axesm() mapshow() scaleruler... but you should consider using a function to display the map in a map axes instead of mapshow

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Songqiu 2022-11-13

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Dear Walter,

Thank you very much for your answer.

I have a polygon vector dataset with a local Projected Coordinate System: JGD_2011_Japan_Zone_8 (EPSG code 6676). And I wrote the following codes to generate a figure:

load('D:\Rinsouzu\Test.mat', 'ClassName', 'ClassCode')
PC = readgeotable('D:\Rinsouzu\Takapyou1\CHM25cmOk_TreeCrown_2C_Rinsou.shp');
uID = unique(PC.RinsouCode);
uID = uID(uID > 0);
ListClass = {'y', 'c', 'r', 'b', 'm', 'k'};
Temp = cell(numel(uID), 1);
N = 1;
Fig = figure;
% ax = axesm('MapProjection', 'tranmerc');
for i = 1 : numel(uID)
    Temp{i} = ClassName(ClassCode == uID(i));
    Idx = PC.RinsouCode == uID(i);
    if Temp{i} == "Akamatsu"
        h(N) = mapshow(PC(Idx, :), 'FaceColor', ListClass{1}, 'FaceAlpha', 1);
        N = N + 1;
    elseif Temp{i} == "Hinoki"
        h(N) = mapshow(PC(Idx, :), 'FaceColor', ListClass{2}, 'FaceAlpha', 1);
        N = N + 1;
    elseif Temp{i} == "Karamatsu"
        h(N) = mapshow(PC(Idx, :), 'FaceColor', ListClass{3}, 'FaceAlpha', 1);
        N = N + 1;
    elseif Temp{i} == "Kouyoujyu"
        h(N) = mapshow(PC(Idx, :), 'FaceColor', ListClass{4}, 'FaceAlpha', 1);
        N = N + 1;
    elseif Temp{i} == "Sugi"
        h(N) = mapshow(PC(Idx, :), 'FaceColor', ListClass{5}, 'FaceAlpha', 1);
        N = N + 1;
    else
        h(N) = mapshow(PC(Idx, :), 'FaceColor', ListClass{6}, 'FaceAlpha', 1);
        N = N + 1;
    end
end
lgd = legend(h, Temp, 'Location', 'northeastoutside');
title(lgd, 'Legend')
box on
grid on
grid minor

Then, I got the following result that I want:

When I turn on the line: [ax = axesm('MapProjection', 'tranmerc');] that you told me, eventhough the codes can run normally, I lost the axis labels and grid lines as follows:

If I continue to run the following codes to add a scalebar and northarrow, I got the following bad result and error:

%%
scaleruler on
scaleruler('units', 'meter');
setm(handlem("scaleruler"), "XLoc", 1700, "YLoc", 91100, "MajorTick", 0 : 20 : 100, "FontSize", 8)
northarrow

My purpose is very simply that is to add a scalebar and a northarrow on the first map of the above figures.

Could you please have a look at my codes and tell me how to improve it for my purpose?

Thanks a lot.

Walter Roberson 2022-11-18

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scaleruler on
scaleruler('units', 'meter');

That is creating two scale rulers, one on the first call and one on the second call. Then handlem() is retrieving both of them, and setm() is giving an error because setm() is giving an error because it expects a scalar.

Remove the first of the calls to remove the error message.

Songqiu 2022-11-21